// SPDX-License-Identifier: GPL-2.0-only
#include <crypto/hash.h>
#include <linux/export.h>
#include <linux/bvec.h>
#include <linux/fault-inject-usercopy.h>
#include <linux/uio.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/splice.h>
#include <linux/compat.h>
#include <net/checksum.h>
#include <linux/scatterlist.h>
#include <linux/instrumented.h>

#define PIPE_PARANOIA /* for now */

/* covers iovec and kvec alike */
#define iterate_iovec(i, n, base, len, off, __p, STEP) {        \
        size_t off = 0;                                         \
        size_t skip = i->iov_offset;                            \
        do {                                                    \
                len = min(n, __p->iov_len - skip);              \
                if (likely(len)) {                              \
                        base = __p->iov_base + skip;            \
                        len -= (STEP);                          \
                        off += len;                             \
                        skip += len;                            \
                        n -= len;                               \
                        if (skip < __p->iov_len)                \
                                break;                          \
                }                                               \
                __p++;                                          \
                skip = 0;                                       \
        } while (n);                                            \
        i->iov_offset = skip;                                   \
        n = off;                                                \
}

#define iterate_bvec(i, n, base, len, off, p, STEP) {           \
        size_t off = 0;                                         \
        unsigned skip = i->iov_offset;                          \
        while (n) {                                             \
                unsigned offset = p->bv_offset + skip;          \
                unsigned left;                                  \
                void *kaddr = kmap_local_page(p->bv_page +      \
                                        offset / PAGE_SIZE);    \
                base = kaddr + offset % PAGE_SIZE;              \
                len = min(min(n, (size_t)(p->bv_len - skip)),   \
                     (size_t)(PAGE_SIZE - offset % PAGE_SIZE)); \
                left = (STEP);                                  \
                kunmap_local(kaddr);                            \
                len -= left;                                    \
                off += len;                                     \
                skip += len;                                    \
                if (skip == p->bv_len) {                        \
                        skip = 0;                               \
                        p++;                                    \
                }                                               \
                n -= len;                                       \
                if (left)                                       \
                        break;                                  \
        }                                                       \
        i->iov_offset = skip;                                   \
        n = off;                                                \
}

#define iterate_xarray(i, n, base, len, __off, STEP) {          \
        __label__ __out;                                        \
        size_t __off = 0;                                       \
        struct page *head = NULL;                               \
        loff_t start = i->xarray_start + i->iov_offset;         \
        unsigned offset = start % PAGE_SIZE;                    \
        pgoff_t index = start / PAGE_SIZE;                      \
        int j;                                                  \
                                                                \
        XA_STATE(xas, i->xarray, index);                        \
                                                                \
        rcu_read_lock();                                        \
        xas_for_each(&xas, head, ULONG_MAX) {                   \
                unsigned left;                                  \
                if (xas_retry(&xas, head))                      \
                        continue;                               \
                if (WARN_ON(xa_is_value(head)))                 \
                        break;                                  \
                if (WARN_ON(PageHuge(head)))                    \
                        break;                                  \
                for (j = (head->index < index) ? index - head->index : 0; \
                     j < thp_nr_pages(head); j++) {             \
                        void *kaddr = kmap_local_page(head + j);        \
                        base = kaddr + offset;                  \
                        len = PAGE_SIZE - offset;               \
                        len = min(n, len);                      \
                        left = (STEP);                          \
                        kunmap_local(kaddr);                    \
                        len -= left;                            \
                        __off += len;                           \
                        n -= len;                               \
                        if (left || n == 0)                     \
                                goto __out;                     \
                        offset = 0;                             \
                }                                               \
        }                                                       \
__out:                                                          \
        rcu_read_unlock();                                      \
        i->iov_offset += __off;                                         \
        n = __off;                                              \
}

#define __iterate_and_advance(i, n, base, len, off, I, K) {     \
        if (unlikely(i->count < n))                             \
                n = i->count;                                   \
        if (likely(n)) {                                        \
                if (likely(iter_is_iovec(i))) {                 \
                        const struct iovec *iov = i->iov;       \
                        void __user *base;                      \
                        size_t len;                             \
                        iterate_iovec(i, n, base, len, off,     \
                                                iov, (I))       \
                        i->nr_segs -= iov - i->iov;             \
                        i->iov = iov;                           \
                } else if (iov_iter_is_bvec(i)) {               \
                        const struct bio_vec *bvec = i->bvec;   \
                        void *base;                             \
                        size_t len;                             \
                        iterate_bvec(i, n, base, len, off,      \
                                                bvec, (K))      \
                        i->nr_segs -= bvec - i->bvec;           \
                        i->bvec = bvec;                         \
                } else if (iov_iter_is_kvec(i)) {               \
                        const struct kvec *kvec = i->kvec;      \
                        void *base;                             \
                        size_t len;                             \
                        iterate_iovec(i, n, base, len, off,     \
                                                kvec, (K))      \
                        i->nr_segs -= kvec - i->kvec;           \
                        i->kvec = kvec;                         \
                } else if (iov_iter_is_xarray(i)) {             \
                        void *base;                             \
                        size_t len;                             \
                        iterate_xarray(i, n, base, len, off,    \
                                                        (K))    \
                }                                               \
                i->count -= n;                                  \
        }                                                       \
}
#define iterate_and_advance(i, n, base, len, off, I, K) \
        __iterate_and_advance(i, n, base, len, off, I, ((void)(K),0))

static int copyout(void __user *to, const void *from, size_t n)
{
        if (should_fail_usercopy())
                return n;
        if (access_ok(to, n)) {
                instrument_copy_to_user(to, from, n);
                n = raw_copy_to_user(to, from, n);
        }
        return n;
}

static int copyin(void *to, const void __user *from, size_t n)
{
        if (should_fail_usercopy())
                return n;
        if (access_ok(from, n)) {
                instrument_copy_from_user(to, from, n);
                n = raw_copy_from_user(to, from, n);
        }
        return n;
}

static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
{
        size_t skip, copy, left, wanted;
        const struct iovec *iov;
        char __user *buf;
        void *kaddr, *from;

        if (unlikely(bytes > i->count))
                bytes = i->count;

        if (unlikely(!bytes))
                return 0;

        might_fault();
        wanted = bytes;
        iov = i->iov;
        skip = i->iov_offset;
        buf = iov->iov_base + skip;
        copy = min(bytes, iov->iov_len - skip);

        if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_writeable(buf, copy)) {
                kaddr = kmap_atomic(page);
                from = kaddr + offset;

                /* first chunk, usually the only one */
                left = copyout(buf, from, copy);
                copy -= left;
                skip += copy;
                from += copy;
                bytes -= copy;

                while (unlikely(!left && bytes)) {
                        iov++;
                        buf = iov->iov_base;
                        copy = min(bytes, iov->iov_len);
                        left = copyout(buf, from, copy);
                        copy -= left;
                        skip = copy;
                        from += copy;
                        bytes -= copy;
                }
                if (likely(!bytes)) {
                        kunmap_atomic(kaddr);
                        goto done;
                }
                offset = from - kaddr;
                buf += copy;
                kunmap_atomic(kaddr);
                copy = min(bytes, iov->iov_len - skip);
        }
        /* Too bad - revert to non-atomic kmap */

        kaddr = kmap(page);
        from = kaddr + offset;
        left = copyout(buf, from, copy);
        copy -= left;
        skip += copy;
        from += copy;
        bytes -= copy;
        while (unlikely(!left && bytes)) {
                iov++;
                buf = iov->iov_base;
                copy = min(bytes, iov->iov_len);
                left = copyout(buf, from, copy);
                copy -= left;
                skip = copy;
                from += copy;
                bytes -= copy;
        }
        kunmap(page);

done:
        if (skip == iov->iov_len) {
                iov++;
                skip = 0;
        }
        i->count -= wanted - bytes;
        i->nr_segs -= iov - i->iov;
        i->iov = iov;
        i->iov_offset = skip;
        return wanted - bytes;
}

static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
{
        size_t skip, copy, left, wanted;
        const struct iovec *iov;
        char __user *buf;
        void *kaddr, *to;

        if (unlikely(bytes > i->count))
                bytes = i->count;

        if (unlikely(!bytes))
                return 0;

        might_fault();
        wanted = bytes;
        iov = i->iov;
        skip = i->iov_offset;
        buf = iov->iov_base + skip;
        copy = min(bytes, iov->iov_len - skip);

        if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_readable(buf, copy)) {
                kaddr = kmap_atomic(page);
                to = kaddr + offset;

                /* first chunk, usually the only one */
                left = copyin(to, buf, copy);
                copy -= left;
                skip += copy;
                to += copy;
                bytes -= copy;

                while (unlikely(!left && bytes)) {
                        iov++;
                        buf = iov->iov_base;
                        copy = min(bytes, iov->iov_len);
                        left = copyin(to, buf, copy);
                        copy -= left;
                        skip = copy;
                        to += copy;
                        bytes -= copy;
                }
                if (likely(!bytes)) {
                        kunmap_atomic(kaddr);
                        goto done;
                }
                offset = to - kaddr;
                buf += copy;
                kunmap_atomic(kaddr);
                copy = min(bytes, iov->iov_len - skip);
        }
        /* Too bad - revert to non-atomic kmap */

        kaddr = kmap(page);
        to = kaddr + offset;
        left = copyin(to, buf, copy);
        copy -= left;
        skip += copy;
        to += copy;
        bytes -= copy;
        while (unlikely(!left && bytes)) {
                iov++;
                buf = iov->iov_base;
                copy = min(bytes, iov->iov_len);
                left = copyin(to, buf, copy);
                copy -= left;
                skip = copy;
                to += copy;
                bytes -= copy;
        }
        kunmap(page);

done:
        if (skip == iov->iov_len) {
                iov++;
                skip = 0;
        }
        i->count -= wanted - bytes;
        i->nr_segs -= iov - i->iov;
        i->iov = iov;
        i->iov_offset = skip;
        return wanted - bytes;
}

#ifdef PIPE_PARANOIA
static bool sanity(const struct iov_iter *i)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_head = pipe->head;
        unsigned int p_tail = pipe->tail;
        unsigned int p_mask = pipe->ring_size - 1;
        unsigned int p_occupancy = pipe_occupancy(p_head, p_tail);
        unsigned int i_head = i->head;
        unsigned int idx;

        if (i->iov_offset) {
                struct pipe_buffer *p;
                if (unlikely(p_occupancy == 0))
                        goto Bad;       // pipe must be non-empty
                if (unlikely(i_head != p_head - 1))
                        goto Bad;       // must be at the last buffer...

                p = &pipe->bufs[i_head & p_mask];
                if (unlikely(p->offset + p->len != i->iov_offset))
                        goto Bad;       // ... at the end of segment
        } else {
                if (i_head != p_head)
                        goto Bad;       // must be right after the last buffer
        }
        return true;
Bad:
        printk(KERN_ERR "idx = %d, offset = %zd\n", i_head, i->iov_offset);
        printk(KERN_ERR "head = %d, tail = %d, buffers = %d\n",
                        p_head, p_tail, pipe->ring_size);
        for (idx = 0; idx < pipe->ring_size; idx++)
                printk(KERN_ERR "[%p %p %d %d]\n",
                        pipe->bufs[idx].ops,
                        pipe->bufs[idx].page,
                        pipe->bufs[idx].offset,
                        pipe->bufs[idx].len);
        WARN_ON(1);
        return false;
}
#else
#define sanity(i) true
#endif

static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
{
        struct pipe_inode_info *pipe = i->pipe;
        struct pipe_buffer *buf;
        unsigned int p_tail = pipe->tail;
        unsigned int p_mask = pipe->ring_size - 1;
        unsigned int i_head = i->head;
        size_t off;

        if (unlikely(bytes > i->count))
                bytes = i->count;

        if (unlikely(!bytes))
                return 0;

        if (!sanity(i))
                return 0;

        off = i->iov_offset;
        buf = &pipe->bufs[i_head & p_mask];
        if (off) {
                if (offset == off && buf->page == page) {
                        /* merge with the last one */
                        buf->len += bytes;
                        i->iov_offset += bytes;
                        goto out;
                }
                i_head++;
                buf = &pipe->bufs[i_head & p_mask];
        }
        if (pipe_full(i_head, p_tail, pipe->max_usage))
                return 0;

        buf->ops = &page_cache_pipe_buf_ops;
        get_page(page);
        buf->page = page;
        buf->offset = offset;
        buf->len = bytes;

        pipe->head = i_head + 1;
        i->iov_offset = offset + bytes;
        i->head = i_head;
out:
        i->count -= bytes;
        return bytes;
}

/*
 * Fault in one or more iovecs of the given iov_iter, to a maximum length of
 * bytes.  For each iovec, fault in each page that constitutes the iovec.
 *
 * Return 0 on success, or non-zero if the memory could not be accessed (i.e.
 * because it is an invalid address).
 */
int iov_iter_fault_in_readable(const struct iov_iter *i, size_t bytes)
{
        if (iter_is_iovec(i)) {
                const struct iovec *p;
                size_t skip;

                if (bytes > i->count)
                        bytes = i->count;
                for (p = i->iov, skip = i->iov_offset; bytes; p++, skip = 0) {
                        size_t len = min(bytes, p->iov_len - skip);
                        int err;

                        if (unlikely(!len))
                                continue;
                        err = fault_in_pages_readable(p->iov_base + skip, len);
                        if (unlikely(err))
                                return err;
                        bytes -= len;
                }
        }
        return 0;
}
EXPORT_SYMBOL(iov_iter_fault_in_readable);

void iov_iter_init(struct iov_iter *i, unsigned int direction,
                        const struct iovec *iov, unsigned long nr_segs,
                        size_t count)
{
        WARN_ON(direction & ~(READ | WRITE));
        *i = (struct iov_iter) {
                .iter_type = ITER_IOVEC,
                .data_source = direction,
                .iov = iov,
                .nr_segs = nr_segs,
                .iov_offset = 0,
                .count = count
        };
}
EXPORT_SYMBOL(iov_iter_init);

static inline bool allocated(struct pipe_buffer *buf)
{
        return buf->ops == &default_pipe_buf_ops;
}

static inline void data_start(const struct iov_iter *i,
                              unsigned int *iter_headp, size_t *offp)
{
        unsigned int p_mask = i->pipe->ring_size - 1;
        unsigned int iter_head = i->head;
        size_t off = i->iov_offset;

        if (off && (!allocated(&i->pipe->bufs[iter_head & p_mask]) ||
                    off == PAGE_SIZE)) {
                iter_head++;
                off = 0;
        }
        *iter_headp = iter_head;
        *offp = off;
}

static size_t push_pipe(struct iov_iter *i, size_t size,
                        int *iter_headp, size_t *offp)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_tail = pipe->tail;
        unsigned int p_mask = pipe->ring_size - 1;
        unsigned int iter_head;
        size_t off;
        ssize_t left;

        if (unlikely(size > i->count))
                size = i->count;
        if (unlikely(!size))
                return 0;

        left = size;
        data_start(i, &iter_head, &off);
        *iter_headp = iter_head;
        *offp = off;
        if (off) {
                left -= PAGE_SIZE - off;
                if (left <= 0) {
                        pipe->bufs[iter_head & p_mask].len += size;
                        return size;
                }
                pipe->bufs[iter_head & p_mask].len = PAGE_SIZE;
                iter_head++;
        }
        while (!pipe_full(iter_head, p_tail, pipe->max_usage)) {
                struct pipe_buffer *buf = &pipe->bufs[iter_head & p_mask];
                struct page *page = alloc_page(GFP_USER);
                if (!page)
                        break;

                buf->ops = &default_pipe_buf_ops;
                buf->page = page;
                buf->offset = 0;
                buf->len = min_t(ssize_t, left, PAGE_SIZE);
                left -= buf->len;
                iter_head++;
                pipe->head = iter_head;

                if (left == 0)
                        return size;
        }
        return size - left;
}

static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
                                struct iov_iter *i)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_mask = pipe->ring_size - 1;
        unsigned int i_head;
        size_t n, off;

        if (!sanity(i))
                return 0;

        bytes = n = push_pipe(i, bytes, &i_head, &off);
        if (unlikely(!n))
                return 0;
        do {
                size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
                memcpy_to_page(pipe->bufs[i_head & p_mask].page, off, addr, chunk);
                i->head = i_head;
                i->iov_offset = off + chunk;
                n -= chunk;
                addr += chunk;
                off = 0;
                i_head++;
        } while (n);
        i->count -= bytes;
        return bytes;
}

static __wsum csum_and_memcpy(void *to, const void *from, size_t len,
                              __wsum sum, size_t off)
{
        __wsum next = csum_partial_copy_nocheck(from, to, len);
        return csum_block_add(sum, next, off);
}

static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
                                         struct iov_iter *i, __wsum *sump)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_mask = pipe->ring_size - 1;
        __wsum sum = *sump;
        size_t off = 0;
        unsigned int i_head;
        size_t r;

        if (!sanity(i))
                return 0;

        bytes = push_pipe(i, bytes, &i_head, &r);
        while (bytes) {
                size_t chunk = min_t(size_t, bytes, PAGE_SIZE - r);
                char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
                sum = csum_and_memcpy(p + r, addr + off, chunk, sum, off);
                kunmap_local(p);
                i->head = i_head;
                i->iov_offset = r + chunk;
                bytes -= chunk;
                off += chunk;
                r = 0;
                i_head++;
        }
        *sump = sum;
        i->count -= off;
        return off;
}

size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
{
        if (unlikely(iov_iter_is_pipe(i)))
                return copy_pipe_to_iter(addr, bytes, i);
        if (iter_is_iovec(i))
                might_fault();
        iterate_and_advance(i, bytes, base, len, off,
                copyout(base, addr + off, len),
                memcpy(base, addr + off, len)
        )

        return bytes;
}
EXPORT_SYMBOL(_copy_to_iter);

#ifdef CONFIG_ARCH_HAS_COPY_MC
static int copyout_mc(void __user *to, const void *from, size_t n)
{
        if (access_ok(to, n)) {
                instrument_copy_to_user(to, from, n);
                n = copy_mc_to_user((__force void *) to, from, n);
        }
        return n;
}

static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
                                struct iov_iter *i)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_mask = pipe->ring_size - 1;
        unsigned int i_head;
        size_t n, off, xfer = 0;

        if (!sanity(i))
                return 0;

        n = push_pipe(i, bytes, &i_head, &off);
        while (n) {
                size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
                char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
                unsigned long rem;
                rem = copy_mc_to_kernel(p + off, addr + xfer, chunk);
                chunk -= rem;
                kunmap_local(p);
                i->head = i_head;
                i->iov_offset = off + chunk;
                xfer += chunk;
                if (rem)
                        break;
                n -= chunk;
                off = 0;
                i_head++;
        }
        i->count -= xfer;
        return xfer;
}

/**
 * _copy_mc_to_iter - copy to iter with source memory error exception handling
 * @addr: source kernel address
 * @bytes: total transfer length
 * @i: destination iterator
 *
 * The pmem driver deploys this for the dax operation
 * (dax_copy_to_iter()) for dax reads (bypass page-cache and the
 * block-layer). Upon #MC read(2) aborts and returns EIO or the bytes
 * successfully copied.
 *
 * The main differences between this and typical _copy_to_iter().
 *
 * * Typical tail/residue handling after a fault retries the copy
 *   byte-by-byte until the fault happens again. Re-triggering machine
 *   checks is potentially fatal so the implementation uses source
 *   alignment and poison alignment assumptions to avoid re-triggering
 *   hardware exceptions.
 *
 * * ITER_KVEC, ITER_PIPE, and ITER_BVEC can return short copies.
 *   Compare to copy_to_iter() where only ITER_IOVEC attempts might return
 *   a short copy.
 *
 * Return: number of bytes copied (may be %0)
 */
size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
{
        if (unlikely(iov_iter_is_pipe(i)))
                return copy_mc_pipe_to_iter(addr, bytes, i);
        if (iter_is_iovec(i))
                might_fault();
        __iterate_and_advance(i, bytes, base, len, off,
                copyout_mc(base, addr + off, len),
                copy_mc_to_kernel(base, addr + off, len)
        )

        return bytes;
}
EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
#endif /* CONFIG_ARCH_HAS_COPY_MC */

size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
{
        if (unlikely(iov_iter_is_pipe(i))) {
                WARN_ON(1);
                return 0;
        }
        if (iter_is_iovec(i))
                might_fault();
        iterate_and_advance(i, bytes, base, len, off,
                copyin(addr + off, base, len),
                memcpy(addr + off, base, len)
        )

        return bytes;
}
EXPORT_SYMBOL(_copy_from_iter);

size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
{
        if (unlikely(iov_iter_is_pipe(i))) {
                WARN_ON(1);
                return 0;
        }
        iterate_and_advance(i, bytes, base, len, off,
                __copy_from_user_inatomic_nocache(addr + off, base, len),
                memcpy(addr + off, base, len)
        )

        return bytes;
}
EXPORT_SYMBOL(_copy_from_iter_nocache);

#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
/**
 * _copy_from_iter_flushcache - write destination through cpu cache
 * @addr: destination kernel address
 * @bytes: total transfer length
 * @i: source iterator
 *
 * The pmem driver arranges for filesystem-dax to use this facility via
 * dax_copy_from_iter() for ensuring that writes to persistent memory
 * are flushed through the CPU cache. It is differentiated from
 * _copy_from_iter_nocache() in that guarantees all data is flushed for
 * all iterator types. The _copy_from_iter_nocache() only attempts to
 * bypass the cache for the ITER_IOVEC case, and on some archs may use
 * instructions that strand dirty-data in the cache.
 *
 * Return: number of bytes copied (may be %0)
 */
size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
{
        if (unlikely(iov_iter_is_pipe(i))) {
                WARN_ON(1);
                return 0;
        }
        iterate_and_advance(i, bytes, base, len, off,
                __copy_from_user_flushcache(addr + off, base, len),
                memcpy_flushcache(addr + off, base, len)
        )

        return bytes;
}
EXPORT_SYMBOL_GPL(_copy_from_iter_flushcache);
#endif

static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
{
        struct page *head;
        size_t v = n + offset;

        /*
         * The general case needs to access the page order in order
         * to compute the page size.
         * However, we mostly deal with order-0 pages and thus can
         * avoid a possible cache line miss for requests that fit all
         * page orders.
         */
        if (n <= v && v <= PAGE_SIZE)
                return true;

        head = compound_head(page);
        v += (page - head) << PAGE_SHIFT;

        if (likely(n <= v && v <= (page_size(head))))
                return true;
        WARN_ON(1);
        return false;
}

static size_t __copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
{
        if (likely(iter_is_iovec(i)))
                return copy_page_to_iter_iovec(page, offset, bytes, i);
        if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
                void *kaddr = kmap_local_page(page);
                size_t wanted = _copy_to_iter(kaddr + offset, bytes, i);
                kunmap_local(kaddr);
                return wanted;
        }
        if (iov_iter_is_pipe(i))
                return copy_page_to_iter_pipe(page, offset, bytes, i);
        if (unlikely(iov_iter_is_discard(i))) {
                if (unlikely(i->count < bytes))
                        bytes = i->count;
                i->count -= bytes;
                return bytes;
        }
        WARN_ON(1);
        return 0;
}

size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
{
        size_t res = 0;
        if (unlikely(!page_copy_sane(page, offset, bytes)))
                return 0;
        page += offset / PAGE_SIZE; // first subpage
        offset %= PAGE_SIZE;
        while (1) {
                size_t n = __copy_page_to_iter(page, offset,
                                min(bytes, (size_t)PAGE_SIZE - offset), i);
                res += n;
                bytes -= n;
                if (!bytes || !n)
                        break;
                offset += n;
                if (offset == PAGE_SIZE) {
                        page++;
                        offset = 0;
                }
        }
        return res;
}
EXPORT_SYMBOL(copy_page_to_iter);

size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
{
        if (unlikely(!page_copy_sane(page, offset, bytes)))
                return 0;
        if (likely(iter_is_iovec(i)))
                return copy_page_from_iter_iovec(page, offset, bytes, i);
        if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
                void *kaddr = kmap_local_page(page);
                size_t wanted = _copy_from_iter(kaddr + offset, bytes, i);
                kunmap_local(kaddr);
                return wanted;
        }
        WARN_ON(1);
        return 0;
}
EXPORT_SYMBOL(copy_page_from_iter);

static size_t pipe_zero(size_t bytes, struct iov_iter *i)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_mask = pipe->ring_size - 1;
        unsigned int i_head;
        size_t n, off;

        if (!sanity(i))
                return 0;

        bytes = n = push_pipe(i, bytes, &i_head, &off);
        if (unlikely(!n))
                return 0;

        do {
                size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
                char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
                memset(p + off, 0, chunk);
                kunmap_local(p);
                i->head = i_head;
                i->iov_offset = off + chunk;
                n -= chunk;
                off = 0;
                i_head++;
        } while (n);
        i->count -= bytes;
        return bytes;
}

size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
{
        if (unlikely(iov_iter_is_pipe(i)))
                return pipe_zero(bytes, i);
        iterate_and_advance(i, bytes, base, len, count,
                clear_user(base, len),
                memset(base, 0, len)
        )

        return bytes;
}
EXPORT_SYMBOL(iov_iter_zero);

size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t bytes,
                                  struct iov_iter *i)
{
        char *kaddr = kmap_atomic(page), *p = kaddr + offset;
        if (unlikely(!page_copy_sane(page, offset, bytes))) {
                kunmap_atomic(kaddr);
                return 0;
        }
        if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
                kunmap_atomic(kaddr);
                WARN_ON(1);
                return 0;
        }
        iterate_and_advance(i, bytes, base, len, off,
                copyin(p + off, base, len),
                memcpy(p + off, base, len)
        )
        kunmap_atomic(kaddr);
        return bytes;
}
EXPORT_SYMBOL(copy_page_from_iter_atomic);

static inline void pipe_truncate(struct iov_iter *i)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_tail = pipe->tail;
        unsigned int p_head = pipe->head;
        unsigned int p_mask = pipe->ring_size - 1;

        if (!pipe_empty(p_head, p_tail)) {
                struct pipe_buffer *buf;
                unsigned int i_head = i->head;
                size_t off = i->iov_offset;

                if (off) {
                        buf = &pipe->bufs[i_head & p_mask];
                        buf->len = off - buf->offset;
                        i_head++;
                }
                while (p_head != i_head) {
                        p_head--;
                        pipe_buf_release(pipe, &pipe->bufs[p_head & p_mask]);
                }

                pipe->head = p_head;
        }
}

static void pipe_advance(struct iov_iter *i, size_t size)
{
        struct pipe_inode_info *pipe = i->pipe;
        if (size) {
                struct pipe_buffer *buf;
                unsigned int p_mask = pipe->ring_size - 1;
                unsigned int i_head = i->head;
                size_t off = i->iov_offset, left = size;

                if (off) /* make it relative to the beginning of buffer */
                        left += off - pipe->bufs[i_head & p_mask].offset;
                while (1) {
                        buf = &pipe->bufs[i_head & p_mask];
                        if (left <= buf->len)
                                break;
                        left -= buf->len;
                        i_head++;
                }
                i->head = i_head;
                i->iov_offset = buf->offset + left;
        }
        i->count -= size;
        /* ... and discard everything past that point */
        pipe_truncate(i);
}

static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
{
        struct bvec_iter bi;

        bi.bi_size = i->count;
        bi.bi_bvec_done = i->iov_offset;
        bi.bi_idx = 0;
        bvec_iter_advance(i->bvec, &bi, size);

        i->bvec += bi.bi_idx;
        i->nr_segs -= bi.bi_idx;
        i->count = bi.bi_size;
        i->iov_offset = bi.bi_bvec_done;
}

static void iov_iter_iovec_advance(struct iov_iter *i, size_t size)
{
        const struct iovec *iov, *end;

        if (!i->count)
                return;
        i->count -= size;

        size += i->iov_offset; // from beginning of current segment
        for (iov = i->iov, end = iov + i->nr_segs; iov < end; iov++) {
                if (likely(size < iov->iov_len))
                        break;
                size -= iov->iov_len;
        }
        i->iov_offset = size;
        i->nr_segs -= iov - i->iov;
        i->iov = iov;
}

void iov_iter_advance(struct iov_iter *i, size_t size)
{
        if (unlikely(i->count < size))
                size = i->count;
        if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
                /* iovec and kvec have identical layouts */
                iov_iter_iovec_advance(i, size);
        } else if (iov_iter_is_bvec(i)) {
                iov_iter_bvec_advance(i, size);
        } else if (iov_iter_is_pipe(i)) {
                pipe_advance(i, size);
        } else if (unlikely(iov_iter_is_xarray(i))) {
                i->iov_offset += size;
                i->count -= size;
        } else if (iov_iter_is_discard(i)) {
                i->count -= size;
        }
}
EXPORT_SYMBOL(iov_iter_advance);

void iov_iter_revert(struct iov_iter *i, size_t unroll)
{
        if (!unroll)
                return;
        if (WARN_ON(unroll > MAX_RW_COUNT))
                return;
        i->count += unroll;
        if (unlikely(iov_iter_is_pipe(i))) {
                struct pipe_inode_info *pipe = i->pipe;
                unsigned int p_mask = pipe->ring_size - 1;
                unsigned int i_head = i->head;
                size_t off = i->iov_offset;
                while (1) {
                        struct pipe_buffer *b = &pipe->bufs[i_head & p_mask];
                        size_t n = off - b->offset;
                        if (unroll < n) {
                                off -= unroll;
                                break;
                        }
                        unroll -= n;
                        if (!unroll && i_head == i->start_head) {
                                off = 0;
                                break;
                        }
                        i_head--;
                        b = &pipe->bufs[i_head & p_mask];
                        off = b->offset + b->len;
                }
                i->iov_offset = off;
                i->head = i_head;
                pipe_truncate(i);
                return;
        }
        if (unlikely(iov_iter_is_discard(i)))
                return;
        if (unroll <= i->iov_offset) {
                i->iov_offset -= unroll;
                return;
        }
        unroll -= i->iov_offset;
        if (iov_iter_is_xarray(i)) {
                BUG(); /* We should never go beyond the start of the specified
                        * range since we might then be straying into pages that
                        * aren't pinned.
                        */
        } else if (iov_iter_is_bvec(i)) {
                const struct bio_vec *bvec = i->bvec;
                while (1) {
                        size_t n = (--bvec)->bv_len;
                        i->nr_segs++;
                        if (unroll <= n) {
                                i->bvec = bvec;
                                i->iov_offset = n - unroll;
                                return;
                        }
                        unroll -= n;
                }
        } else { /* same logics for iovec and kvec */
                const struct iovec *iov = i->iov;
                while (1) {
                        size_t n = (--iov)->iov_len;
                        i->nr_segs++;
                        if (unroll <= n) {
                                i->iov = iov;
                                i->iov_offset = n - unroll;
                                return;
                        }
                        unroll -= n;
                }
        }
}
EXPORT_SYMBOL(iov_iter_revert);

/*
 * Return the count of just the current iov_iter segment.
 */
size_t iov_iter_single_seg_count(const struct iov_iter *i)
{
        if (i->nr_segs > 1) {
                if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
                        return min(i->count, i->iov->iov_len - i->iov_offset);
                if (iov_iter_is_bvec(i))
                        return min(i->count, i->bvec->bv_len - i->iov_offset);
        }
        return i->count;
}
EXPORT_SYMBOL(iov_iter_single_seg_count);

void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
                        const struct kvec *kvec, unsigned long nr_segs,
                        size_t count)
{
        WARN_ON(direction & ~(READ | WRITE));
        *i = (struct iov_iter){
                .iter_type = ITER_KVEC,
                .data_source = direction,
                .kvec = kvec,
                .nr_segs = nr_segs,
                .iov_offset = 0,
                .count = count
        };
}
EXPORT_SYMBOL(iov_iter_kvec);

void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
                        const struct bio_vec *bvec, unsigned long nr_segs,
                        size_t count)
{
        WARN_ON(direction & ~(READ | WRITE));
        *i = (struct iov_iter){
                .iter_type = ITER_BVEC,
                .data_source = direction,
                .bvec = bvec,
                .nr_segs = nr_segs,
                .iov_offset = 0,
                .count = count
        };
}
EXPORT_SYMBOL(iov_iter_bvec);

void iov_iter_pipe(struct iov_iter *i, unsigned int direction,
                        struct pipe_inode_info *pipe,
                        size_t count)
{
        BUG_ON(direction != READ);
        WARN_ON(pipe_full(pipe->head, pipe->tail, pipe->ring_size));
        *i = (struct iov_iter){
                .iter_type = ITER_PIPE,
                .data_source = false,
                .pipe = pipe,
                .head = pipe->head,
                .start_head = pipe->head,
                .iov_offset = 0,
                .count = count
        };
}
EXPORT_SYMBOL(iov_iter_pipe);

/**
 * iov_iter_xarray - Initialise an I/O iterator to use the pages in an xarray
 * @i: The iterator to initialise.
 * @direction: The direction of the transfer.
 * @xarray: The xarray to access.
 * @start: The start file position.
 * @count: The size of the I/O buffer in bytes.
 *
 * Set up an I/O iterator to either draw data out of the pages attached to an
 * inode or to inject data into those pages.  The pages *must* be prevented
 * from evaporation, either by taking a ref on them or locking them by the
 * caller.
 */
void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
                     struct xarray *xarray, loff_t start, size_t count)
{
        BUG_ON(direction & ~1);
        *i = (struct iov_iter) {
                .iter_type = ITER_XARRAY,
                .data_source = direction,
                .xarray = xarray,
                .xarray_start = start,
                .count = count,
                .iov_offset = 0
        };
}
EXPORT_SYMBOL(iov_iter_xarray);

/**
 * iov_iter_discard - Initialise an I/O iterator that discards data
 * @i: The iterator to initialise.
 * @direction: The direction of the transfer.
 * @count: The size of the I/O buffer in bytes.
 *
 * Set up an I/O iterator that just discards everything that's written to it.
 * It's only available as a READ iterator.
 */
void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
{
        BUG_ON(direction != READ);
        *i = (struct iov_iter){
                .iter_type = ITER_DISCARD,
                .data_source = false,
                .count = count,
                .iov_offset = 0
        };
}
EXPORT_SYMBOL(iov_iter_discard);

static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
{
        unsigned long res = 0;
        size_t size = i->count;
        size_t skip = i->iov_offset;
        unsigned k;

        for (k = 0; k < i->nr_segs; k++, skip = 0) {
                size_t len = i->iov[k].iov_len - skip;
                if (len) {
                        res |= (unsigned long)i->iov[k].iov_base + skip;
                        if (len > size)
                                len = size;
                        res |= len;
                        size -= len;
                        if (!size)
                                break;
                }
        }
        return res;
}

static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i)
{
        unsigned res = 0;
        size_t size = i->count;
        unsigned skip = i->iov_offset;
        unsigned k;

        for (k = 0; k < i->nr_segs; k++, skip = 0) {
                size_t len = i->bvec[k].bv_len - skip;
                res |= (unsigned long)i->bvec[k].bv_offset + skip;
                if (len > size)
                        len = size;
                res |= len;
                size -= len;
                if (!size)
                        break;
        }
        return res;
}

unsigned long iov_iter_alignment(const struct iov_iter *i)
{
        /* iovec and kvec have identical layouts */
        if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
                return iov_iter_alignment_iovec(i);

        if (iov_iter_is_bvec(i))
                return iov_iter_alignment_bvec(i);

        if (iov_iter_is_pipe(i)) {
                unsigned int p_mask = i->pipe->ring_size - 1;
                size_t size = i->count;

                if (size && i->iov_offset && allocated(&i->pipe->bufs[i->head & p_mask]))
                        return size | i->iov_offset;
                return size;
        }

        if (iov_iter_is_xarray(i))
                return (i->xarray_start + i->iov_offset) | i->count;

        return 0;
}
EXPORT_SYMBOL(iov_iter_alignment);

unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
{
        unsigned long res = 0;
        unsigned long v = 0;
        size_t size = i->count;
        unsigned k;

        if (WARN_ON(!iter_is_iovec(i)))
                return ~0U;

        for (k = 0; k < i->nr_segs; k++) {
                if (i->iov[k].iov_len) {
                        unsigned long base = (unsigned long)i->iov[k].iov_base;
                        if (v) // if not the first one
                                res |= base | v; // this start | previous end
                        v = base + i->iov[k].iov_len;
                        if (size <= i->iov[k].iov_len)
                                break;
                        size -= i->iov[k].iov_len;
                }
        }
        return res;
}
EXPORT_SYMBOL(iov_iter_gap_alignment);

static inline ssize_t __pipe_get_pages(struct iov_iter *i,
                                size_t maxsize,
                                struct page **pages,
                                int iter_head,
                                size_t *start)
{
        struct pipe_inode_info *pipe = i->pipe;
        unsigned int p_mask = pipe->ring_size - 1;
        ssize_t n = push_pipe(i, maxsize, &iter_head, start);
        if (!n)
                return -EFAULT;

        maxsize = n;
        n += *start;
        while (n > 0) {
                get_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
                iter_head++;
                n -= PAGE_SIZE;
        }

        return maxsize;
}

static ssize_t pipe_get_pages(struct iov_iter *i,
                   struct page **pages, size_t maxsize, unsigned maxpages,
                   size_t *start)
{
        unsigned int iter_head, npages;
        size_t capacity;

        if (!sanity(i))
                return -EFAULT;

        data_start(i, &iter_head, start);
        /* Amount of free space: some of this one + all after this one */
        npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
        capacity = min(npages, maxpages) * PAGE_SIZE - *start;

        return __pipe_get_pages(i, min(maxsize, capacity), pages, iter_head, start);
}

static ssize_t iter_xarray_populate_pages(struct page **pages, struct xarray *xa,
                                          pgoff_t index, unsigned int nr_pages)
{
        XA_STATE(xas, xa, index);
        struct page *page;
        unsigned int ret = 0;

        rcu_read_lock();
        for (page = xas_load(&xas); page; page = xas_next(&xas)) {
                if (xas_retry(&xas, page))
                        continue;

                /* Has the page moved or been split? */
                if (unlikely(page != xas_reload(&xas))) {
                        xas_reset(&xas);
                        continue;
                }

                pages[ret] = find_subpage(page, xas.xa_index);
                get_page(pages[ret]);
                if (++ret == nr_pages)
                        break;
        }
        rcu_read_unlock();
        return ret;
}

static ssize_t iter_xarray_get_pages(struct iov_iter *i,
                                     struct page **pages, size_t maxsize,
                                     unsigned maxpages, size_t *_start_offset)
{
        unsigned nr, offset;
        pgoff_t index, count;
        size_t size = maxsize, actual;
        loff_t pos;

        if (!size || !maxpages)
                return 0;

        pos = i->xarray_start + i->iov_offset;
        index = pos >> PAGE_SHIFT;
        offset = pos & ~PAGE_MASK;
        *_start_offset = offset;

        count = 1;
        if (size > PAGE_SIZE - offset) {
                size -= PAGE_SIZE - offset;
                count += size >> PAGE_SHIFT;
                size &= ~PAGE_MASK;
                if (size)
                        count++;
        }

        if (count > maxpages)
                count = maxpages;

        nr = iter_xarray_populate_pages(pages, i->xarray, index, count);
        if (nr == 0)
                return 0;

        actual = PAGE_SIZE * nr;
        actual -= offset;
        if (nr == count && size > 0) {
                unsigned last_offset = (nr > 1) ? 0 : offset;
                actual -= PAGE_SIZE - (last_offset + size);
        }
        return actual;
}

/* must be done on non-empty ITER_IOVEC one */
static unsigned long first_iovec_segment(const struct iov_iter *i,
                                         size_t *size, size_t *start,
                                         size_t maxsize, unsigned maxpages)
{
        size_t skip;
        long k;

        for (k = 0, skip = i->iov_offset; k < i->nr_segs; k++, skip = 0) {
                unsigned long addr = (unsigned long)i->iov[k].iov_base + skip;
                size_t len = i->iov[k].iov_len - skip;

                if (unlikely(!len))
                        continue;
                if (len > maxsize)
                        len = maxsize;
                len += (*start = addr % PAGE_SIZE);
                if (len > maxpages * PAGE_SIZE)
                        len = maxpages * PAGE_SIZE;
                *size = len;
                return addr & PAGE_MASK;
        }
        BUG(); // if it had been empty, we wouldn't get called
}

/* must be done on non-empty ITER_BVEC one */
static struct page *first_bvec_segment(const struct iov_iter *i,
                                       size_t *size, size_t *start,
                                       size_t maxsize, unsigned maxpages)
{
        struct page *page;
        size_t skip = i->iov_offset, len;

        len = i->bvec->bv_len - skip;
        if (len > maxsize)
                len = maxsize;
        skip += i->bvec->bv_offset;
        page = i->bvec->bv_page + skip / PAGE_SIZE;
        len += (*start = skip % PAGE_SIZE);
        if (len > maxpages * PAGE_SIZE)
                len = maxpages * PAGE_SIZE;
        *size = len;
        return page;
}

ssize_t iov_iter_get_pages(struct iov_iter *i,
                   struct page **pages, size_t maxsize, unsigned maxpages,
                   size_t *start)
{
        size_t len;
        int n, res;

        if (maxsize > i->count)
                maxsize = i->count;
        if (!maxsize)
                return 0;

        if (likely(iter_is_iovec(i))) {
                unsigned long addr;

                addr = first_iovec_segment(i, &len, start, maxsize, maxpages);
                n = DIV_ROUND_UP(len, PAGE_SIZE);
                res = get_user_pages_fast(addr, n,
                                iov_iter_rw(i) != WRITE ?  FOLL_WRITE : 0,
                                pages);
                if (unlikely(res < 0))
                        return res;
                return (res == n ? len : res * PAGE_SIZE) - *start;
        }
        if (iov_iter_is_bvec(i)) {
                struct page *page;

                page = first_bvec_segment(i, &len, start, maxsize, maxpages);
                n = DIV_ROUND_UP(len, PAGE_SIZE);
                while (n--)
                        get_page(*pages++ = page++);
                return len - *start;
        }
        if (iov_iter_is_pipe(i))
                return pipe_get_pages(i, pages, maxsize, maxpages, start);
        if (iov_iter_is_xarray(i))
                return iter_xarray_get_pages(i, pages, maxsize, maxpages, start);
        return -EFAULT;
}
EXPORT_SYMBOL(iov_iter_get_pages);

static struct page **get_pages_array(size_t n)
{
        return kvmalloc_array(n, sizeof(struct page *), GFP_KERNEL);
}

static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
                   struct page ***pages, size_t maxsize,
                   size_t *start)
{
        struct page **p;
        unsigned int iter_head, npages;
        ssize_t n;

        if (!sanity(i))
                return -EFAULT;

        data_start(i, &iter_head, start);
        /* Amount of free space: some of this one + all after this one */
        npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
        n = npages * PAGE_SIZE - *start;
        if (maxsize > n)
                maxsize = n;
        else
                npages = DIV_ROUND_UP(maxsize + *start, PAGE_SIZE);
        p = get_pages_array(npages);
        if (!p)
                return -ENOMEM;
        n = __pipe_get_pages(i, maxsize, p, iter_head, start);
        if (n > 0)
                *pages = p;
        else
                kvfree(p);
        return n;
}

static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i,
                                           struct page ***pages, size_t maxsize,
                                           size_t *_start_offset)
{
        struct page **p;
        unsigned nr, offset;
        pgoff_t index, count;
        size_t size = maxsize, actual;
        loff_t pos;

        if (!size)
                return 0;

        pos = i->xarray_start + i->iov_offset;
        index = pos >> PAGE_SHIFT;
        offset = pos & ~PAGE_MASK;
        *_start_offset = offset;

        count = 1;
        if (size > PAGE_SIZE - offset) {
                size -= PAGE_SIZE - offset;
                count += size >> PAGE_SHIFT;
                size &= ~PAGE_MASK;
                if (size)
                        count++;
        }

        p = get_pages_array(count);
        if (!p)
                return -ENOMEM;
        *pages = p;

        nr = iter_xarray_populate_pages(p, i->xarray, index, count);
        if (nr == 0)
                return 0;

        actual = PAGE_SIZE * nr;
        actual -= offset;
        if (nr == count && size > 0) {
                unsigned last_offset = (nr > 1) ? 0 : offset;
                actual -= PAGE_SIZE - (last_offset + size);
        }
        return actual;
}

ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
                   struct page ***pages, size_t maxsize,
                   size_t *start)
{
        struct page **p;
        size_t len;
        int n, res;

        if (maxsize > i->count)
                maxsize = i->count;
        if (!maxsize)
                return 0;

        if (likely(iter_is_iovec(i))) {
                unsigned long addr;

                addr = first_iovec_segment(i, &len, start, maxsize, ~0U);
                n = DIV_ROUND_UP(len, PAGE_SIZE);
                p = get_pages_array(n);
                if (!p)
                        return -ENOMEM;
                res = get_user_pages_fast(addr, n,
                                iov_iter_rw(i) != WRITE ?  FOLL_WRITE : 0, p);
                if (unlikely(res < 0)) {
                        kvfree(p);
                        return res;
                }
                *pages = p;
                return (res == n ? len : res * PAGE_SIZE) - *start;
        }
        if (iov_iter_is_bvec(i)) {
                struct page *page;

                page = first_bvec_segment(i, &len, start, maxsize, ~0U);
                n = DIV_ROUND_UP(len, PAGE_SIZE);
                *pages = p = get_pages_array(n);
                if (!p)
                        return -ENOMEM;
                while (n--)
                        get_page(*p++ = page++);
                return len - *start;
        }
        if (iov_iter_is_pipe(i))
                return pipe_get_pages_alloc(i, pages, maxsize, start);
        if (iov_iter_is_xarray(i))
                return iter_xarray_get_pages_alloc(i, pages, maxsize, start);
        return -EFAULT;
}
EXPORT_SYMBOL(iov_iter_get_pages_alloc);

size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
                               struct iov_iter *i)
{
        __wsum sum, next;
        sum = *csum;
        if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
                WARN_ON(1);
                return 0;
        }
        iterate_and_advance(i, bytes, base, len, off, ({
                next = csum_and_copy_from_user(base, addr + off, len);
                sum = csum_block_add(sum, next, off);
                next ? 0 : len;
        }), ({
                sum = csum_and_memcpy(addr + off, base, len, sum, off);
        })
        )
        *csum = sum;
        return bytes;
}
EXPORT_SYMBOL(csum_and_copy_from_iter);

size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate,
                             struct iov_iter *i)
{
        struct csum_state *csstate = _csstate;
        __wsum sum, next;

        if (unlikely(iov_iter_is_discard(i))) {
                WARN_ON(1);     /* for now */
                return 0;
        }

        sum = csum_shift(csstate->csum, csstate->off);
        if (unlikely(iov_iter_is_pipe(i)))
                bytes = csum_and_copy_to_pipe_iter(addr, bytes, i, &sum);
        else iterate_and_advance(i, bytes, base, len, off, ({
                next = csum_and_copy_to_user(addr + off, base, len);
                sum = csum_block_add(sum, next, off);
                next ? 0 : len;
        }), ({
                sum = csum_and_memcpy(base, addr + off, len, sum, off);
        })
        )
        csstate->csum = csum_shift(sum, csstate->off);
        csstate->off += bytes;
        return bytes;
}
EXPORT_SYMBOL(csum_and_copy_to_iter);

size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
                struct iov_iter *i)
{
#ifdef CONFIG_CRYPTO_HASH
        struct ahash_request *hash = hashp;
        struct scatterlist sg;
        size_t copied;

        copied = copy_to_iter(addr, bytes, i);
        sg_init_one(&sg, addr, copied);
        ahash_request_set_crypt(hash, &sg, NULL, copied);
        crypto_ahash_update(hash);
        return copied;
#else
        return 0;
#endif
}
EXPORT_SYMBOL(hash_and_copy_to_iter);

static int iov_npages(const struct iov_iter *i, int maxpages)
{
        size_t skip = i->iov_offset, size = i->count;
        const struct iovec *p;
        int npages = 0;

        for (p = i->iov; size; skip = 0, p++) {
                unsigned offs = offset_in_page(p->iov_base + skip);
                size_t len = min(p->iov_len - skip, size);

                if (len) {
                        size -= len;
                        npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
                        if (unlikely(npages > maxpages))
                                return maxpages;
                }
        }
        return npages;
}

static int bvec_npages(const struct iov_iter *i, int maxpages)
{
        size_t skip = i->iov_offset, size = i->count;
        const struct bio_vec *p;
        int npages = 0;

        for (p = i->bvec; size; skip = 0, p++) {
                unsigned offs = (p->bv_offset + skip) % PAGE_SIZE;
                size_t len = min(p->bv_len - skip, size);

                size -= len;
                npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
                if (unlikely(npages > maxpages))
                        return maxpages;
        }
        return npages;
}

int iov_iter_npages(const struct iov_iter *i, int maxpages)
{
        if (unlikely(!i->count))
                return 0;
        /* iovec and kvec have identical layouts */
        if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
                return iov_npages(i, maxpages);
        if (iov_iter_is_bvec(i))
                return bvec_npages(i, maxpages);
        if (iov_iter_is_pipe(i)) {
                unsigned int iter_head;
                int npages;
                size_t off;

                if (!sanity(i))
                        return 0;

                data_start(i, &iter_head, &off);
                /* some of this one + all after this one */
                npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
                return min(npages, maxpages);
        }
        if (iov_iter_is_xarray(i)) {
                unsigned offset = (i->xarray_start + i->iov_offset) % PAGE_SIZE;
                int npages = DIV_ROUND_UP(offset + i->count, PAGE_SIZE);
                return min(npages, maxpages);
        }
        return 0;
}
EXPORT_SYMBOL(iov_iter_npages);

const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
{
        *new = *old;
        if (unlikely(iov_iter_is_pipe(new))) {
                WARN_ON(1);
                return NULL;
        }
        if (unlikely(iov_iter_is_discard(new) || iov_iter_is_xarray(new)))
                return NULL;
        if (iov_iter_is_bvec(new))
                return new->bvec = kmemdup(new->bvec,
                                    new->nr_segs * sizeof(struct bio_vec),
                                    flags);
        else
                /* iovec and kvec have identical layout */
                return new->iov = kmemdup(new->iov,
                                   new->nr_segs * sizeof(struct iovec),
                                   flags);
}
EXPORT_SYMBOL(dup_iter);

static int copy_compat_iovec_from_user(struct iovec *iov,
                const struct iovec __user *uvec, unsigned long nr_segs)
{
        const struct compat_iovec __user *uiov =
                (const struct compat_iovec __user *)uvec;
        int ret = -EFAULT, i;

        if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
                return -EFAULT;

        for (i = 0; i < nr_segs; i++) {
                compat_uptr_t buf;
                compat_ssize_t len;

                unsafe_get_user(len, &uiov[i].iov_len, uaccess_end);
                unsafe_get_user(buf, &uiov[i].iov_base, uaccess_end);

                /* check for compat_size_t not fitting in compat_ssize_t .. */
                if (len < 0) {
                        ret = -EINVAL;
                        goto uaccess_end;
                }
                iov[i].iov_base = compat_ptr(buf);
                iov[i].iov_len = len;
        }

        ret = 0;
uaccess_end:
        user_access_end();
        return ret;
}

static int copy_iovec_from_user(struct iovec *iov,
                const struct iovec __user *uvec, unsigned long nr_segs)
{
        unsigned long seg;

        if (copy_from_user(iov, uvec, nr_segs * sizeof(*uvec)))
                return -EFAULT;
        for (seg = 0; seg < nr_segs; seg++) {
                if ((ssize_t)iov[seg].iov_len < 0)
                        return -EINVAL;
        }

        return 0;
}

struct iovec *iovec_from_user(const struct iovec __user *uvec,
                unsigned long nr_segs, unsigned long fast_segs,
                struct iovec *fast_iov, bool compat)
{
        struct iovec *iov = fast_iov;
        int ret;

        /*
         * SuS says "The readv() function *may* fail if the iovcnt argument was
         * less than or equal to 0, or greater than {IOV_MAX}.  Linux has
         * traditionally returned zero for zero segments, so...
         */
        if (nr_segs == 0)
                return iov;
        if (nr_segs > UIO_MAXIOV)
                return ERR_PTR(-EINVAL);
        if (nr_segs > fast_segs) {
                iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
                if (!iov)
                        return ERR_PTR(-ENOMEM);
        }

        if (compat)
                ret = copy_compat_iovec_from_user(iov, uvec, nr_segs);
        else
                ret = copy_iovec_from_user(iov, uvec, nr_segs);
        if (ret) {
                if (iov != fast_iov)
                        kfree(iov);
                return ERR_PTR(ret);
        }

        return iov;
}

ssize_t __import_iovec(int type, const struct iovec __user *uvec,
                 unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
                 struct iov_iter *i, bool compat)
{
        ssize_t total_len = 0;
        unsigned long seg;
        struct iovec *iov;

        iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat);
        if (IS_ERR(iov)) {
                *iovp = NULL;
                return PTR_ERR(iov);
        }

        /*
         * According to the Single Unix Specification we should return EINVAL if
         * an element length is < 0 when cast to ssize_t or if the total length
         * would overflow the ssize_t return value of the system call.
         *
         * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
         * overflow case.
         */
        for (seg = 0; seg < nr_segs; seg++) {
                ssize_t len = (ssize_t)iov[seg].iov_len;

                if (!access_ok(iov[seg].iov_base, len)) {
                        if (iov != *iovp)
                                kfree(iov);
                        *iovp = NULL;
                        return -EFAULT;
                }

                if (len > MAX_RW_COUNT - total_len) {
                        len = MAX_RW_COUNT - total_len;
                        iov[seg].iov_len = len;
                }
                total_len += len;
        }

        iov_iter_init(i, type, iov, nr_segs, total_len);
        if (iov == *iovp)
                *iovp = NULL;
        else
                *iovp = iov;
        return total_len;
}

/**
 * import_iovec() - Copy an array of &struct iovec from userspace
 *     into the kernel, check that it is valid, and initialize a new
 *     &struct iov_iter iterator to access it.
 *
 * @type: One of %READ or %WRITE.
 * @uvec: Pointer to the userspace array.
 * @nr_segs: Number of elements in userspace array.
 * @fast_segs: Number of elements in @iov.
 * @iovp: (input and output parameter) Pointer to pointer to (usually small
 *     on-stack) kernel array.
 * @i: Pointer to iterator that will be initialized on success.
 *
 * If the array pointed to by *@iov is large enough to hold all @nr_segs,
 * then this function places %NULL in *@iov on return. Otherwise, a new
 * array will be allocated and the result placed in *@iov. This means that
 * the caller may call kfree() on *@iov regardless of whether the small
 * on-stack array was used or not (and regardless of whether this function
 * returns an error or not).
 *
 * Return: Negative error code on error, bytes imported on success
 */
ssize_t import_iovec(int type, const struct iovec __user *uvec,
                 unsigned nr_segs, unsigned fast_segs,
                 struct iovec **iovp, struct iov_iter *i)
{
        return __import_iovec(type, uvec, nr_segs, fast_segs, iovp, i,
                              in_compat_syscall());
}
EXPORT_SYMBOL(import_iovec);

int import_single_range(int rw, void __user *buf, size_t len,
                 struct iovec *iov, struct iov_iter *i)
{
        if (len > MAX_RW_COUNT)
                len = MAX_RW_COUNT;
        if (unlikely(!access_ok(buf, len)))
                return -EFAULT;

        iov->iov_base = buf;
        iov->iov_len = len;
        iov_iter_init(i, rw, iov, 1, len);
        return 0;
}
EXPORT_SYMBOL(import_single_range);

/**
 * iov_iter_restore() - Restore a &struct iov_iter to the same state as when
 *     iov_iter_save_state() was called.
 *
 * @i: &struct iov_iter to restore
 * @state: state to restore from
 *
 * Used after iov_iter_save_state() to bring restore @i, if operations may
 * have advanced it.
 *
 * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC
 */
void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
{
        if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i)) &&
                         !iov_iter_is_kvec(i))
                return;
        i->iov_offset = state->iov_offset;
        i->count = state->count;
        /*
         * For the *vec iters, nr_segs + iov is constant - if we increment
         * the vec, then we also decrement the nr_segs count. Hence we don't
         * need to track both of these, just one is enough and we can deduct
         * the other from that. ITER_KVEC and ITER_IOVEC are the same struct
         * size, so we can just increment the iov pointer as they are unionzed.

         * ITER_BVEC _may_ be the same size on some archs, but on others it is
         * not. Be safe and handle it separately.
         */
        BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
        if (iov_iter_is_bvec(i))
                i->bvec -= state->nr_segs - i->nr_segs;
        else
                i->iov -= state->nr_segs - i->nr_segs;
        i->nr_segs = state->nr_segs;
}