#include <linux/export.h>
#include <linux/uio.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>

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

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

        if (unlikely(!bytes))
                return 0;

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

        left = __copy_to_user(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 = __copy_to_user(buf, from, copy);
                copy -= left;
                skip = copy;
                from += copy;
                bytes -= copy;
        }

        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_from_iter_iovec(void *to, size_t bytes, struct iov_iter *i)
{
        size_t skip, copy, left, wanted;
        const struct iovec *iov;
        char __user *buf;

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

        if (unlikely(!bytes))
                return 0;

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

        left = __copy_from_user(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 = __copy_from_user(to, buf, copy);
                copy -= left;
                skip = copy;
                to += copy;
                bytes -= copy;
        }

        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_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;

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

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

                /* first chunk, usually the only one */
                left = __copy_to_user_inatomic(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 = __copy_to_user_inatomic(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 = __copy_to_user(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 = __copy_to_user(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;

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

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

                /* first chunk, usually the only one */
                left = __copy_from_user_inatomic(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 = __copy_from_user_inatomic(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 = __copy_from_user(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 = __copy_from_user(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;
}

static size_t zero_iovec(size_t bytes, struct iov_iter *i)
{
        size_t skip, copy, left, wanted;
        const struct iovec *iov;
        char __user *buf;

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

        if (unlikely(!bytes))
                return 0;

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

        left = __clear_user(buf, copy);
        copy -= left;
        skip += copy;
        bytes -= copy;

        while (unlikely(!left && bytes)) {
                iov++;
                buf = iov->iov_base;
                copy = min(bytes, iov->iov_len);
                left = __clear_user(buf, copy);
                copy -= left;
                skip = copy;
                bytes -= copy;
        }

        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 __iovec_copy_from_user_inatomic(char *vaddr,
                        const struct iovec *iov, size_t base, size_t bytes)
{
        size_t copied = 0, left = 0;

        while (bytes) {
                char __user *buf = iov->iov_base + base;
                int copy = min(bytes, iov->iov_len - base);

                base = 0;
                left = __copy_from_user_inatomic(vaddr, buf, copy);
                copied += copy;
                bytes -= copy;
                vaddr += copy;
                iov++;

                if (unlikely(left))
                        break;
        }
        return copied - left;
}

/*
 * Copy as much as we can into the page and return the number of bytes which
 * were successfully copied.  If a fault is encountered then return the number of
 * bytes which were copied.
 */
static size_t copy_from_user_atomic_iovec(struct page *page,
                struct iov_iter *i, unsigned long offset, size_t bytes)
{
        char *kaddr;
        size_t copied;

        kaddr = kmap_atomic(page);
        if (likely(i->nr_segs == 1)) {
                int left;
                char __user *buf = i->iov->iov_base + i->iov_offset;
                left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
                copied = bytes - left;
        } else {
                copied = __iovec_copy_from_user_inatomic(kaddr + offset,
                                                i->iov, i->iov_offset, bytes);
        }
        kunmap_atomic(kaddr);

        return copied;
}

static void advance_iovec(struct iov_iter *i, size_t bytes)
{
        BUG_ON(i->count < bytes);

        if (likely(i->nr_segs == 1)) {
                i->iov_offset += bytes;
                i->count -= bytes;
        } else {
                const struct iovec *iov = i->iov;
                size_t base = i->iov_offset;
                unsigned long nr_segs = i->nr_segs;

                /*
                 * The !iov->iov_len check ensures we skip over unlikely
                 * zero-length segments (without overruning the iovec).
                 */
                while (bytes || unlikely(i->count && !iov->iov_len)) {
                        int copy;

                        copy = min(bytes, iov->iov_len - base);
                        BUG_ON(!i->count || i->count < copy);
                        i->count -= copy;
                        bytes -= copy;
                        base += copy;
                        if (iov->iov_len == base) {
                                iov++;
                                nr_segs--;
                                base = 0;
                        }
                }
                i->iov = iov;
                i->iov_offset = base;
                i->nr_segs = nr_segs;
        }
}

/*
 * Fault in the first iovec of the given iov_iter, to a maximum length
 * of bytes. Returns 0 on success, or non-zero if the memory could not be
 * accessed (ie. because it is an invalid address).
 *
 * writev-intensive code may want this to prefault several iovecs -- that
 * would be possible (callers must not rely on the fact that _only_ the
 * first iovec will be faulted with the current implementation).
 */
int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
{
        if (!(i->type & ITER_BVEC)) {
                char __user *buf = i->iov->iov_base + i->iov_offset;
                bytes = min(bytes, i->iov->iov_len - i->iov_offset);
                return fault_in_pages_readable(buf, bytes);
        }
        return 0;
}
EXPORT_SYMBOL(iov_iter_fault_in_readable);

static unsigned long alignment_iovec(const struct iov_iter *i)
{
        const struct iovec *iov = i->iov;
        unsigned long res;
        size_t size = i->count;
        size_t n;

        if (!size)
                return 0;

        res = (unsigned long)iov->iov_base + i->iov_offset;
        n = iov->iov_len - i->iov_offset;
        if (n >= size)
                return res | size;
        size -= n;
        res |= n;
        while (size > (++iov)->iov_len) {
                res |= (unsigned long)iov->iov_base | iov->iov_len;
                size -= iov->iov_len;
        }
        res |= (unsigned long)iov->iov_base | size;
        return res;
}

void iov_iter_init(struct iov_iter *i, int direction,
                        const struct iovec *iov, unsigned long nr_segs,
                        size_t count)
{
        /* It will get better.  Eventually... */
        if (segment_eq(get_fs(), KERNEL_DS))
                direction |= ITER_KVEC;
        i->type = direction;
        i->iov = iov;
        i->nr_segs = nr_segs;
        i->iov_offset = 0;
        i->count = count;
}
EXPORT_SYMBOL(iov_iter_init);

static ssize_t get_pages_iovec(struct iov_iter *i,
                   struct page **pages, size_t maxsize, unsigned maxpages,
                   size_t *start)
{
        size_t offset = i->iov_offset;
        const struct iovec *iov = i->iov;
        size_t len;
        unsigned long addr;
        int n;
        int res;

        len = iov->iov_len - offset;
        if (len > i->count)
                len = i->count;
        if (len > maxsize)
                len = maxsize;
        addr = (unsigned long)iov->iov_base + offset;
        len += *start = addr & (PAGE_SIZE - 1);
        if (len > maxpages * PAGE_SIZE)
                len = maxpages * PAGE_SIZE;
        addr &= ~(PAGE_SIZE - 1);
        n = (len + PAGE_SIZE - 1) / PAGE_SIZE;
        res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, pages);
        if (unlikely(res < 0))
                return res;
        return (res == n ? len : res * PAGE_SIZE) - *start;
}

static ssize_t get_pages_alloc_iovec(struct iov_iter *i,
                   struct page ***pages, size_t maxsize,
                   size_t *start)
{
        size_t offset = i->iov_offset;
        const struct iovec *iov = i->iov;
        size_t len;
        unsigned long addr;
        void *p;
        int n;
        int res;

        len = iov->iov_len - offset;
        if (len > i->count)
                len = i->count;
        if (len > maxsize)
                len = maxsize;
        addr = (unsigned long)iov->iov_base + offset;
        len += *start = addr & (PAGE_SIZE - 1);
        addr &= ~(PAGE_SIZE - 1);
        n = (len + PAGE_SIZE - 1) / PAGE_SIZE;
        
        p = kmalloc(n * sizeof(struct page *), GFP_KERNEL);
        if (!p)
                p = vmalloc(n * sizeof(struct page *));
        if (!p)
                return -ENOMEM;

        res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, p);
        if (unlikely(res < 0)) {
                kvfree(p);
                return res;
        }
        *pages = p;
        return (res == n ? len : res * PAGE_SIZE) - *start;
}

static int iov_iter_npages_iovec(const struct iov_iter *i, int maxpages)
{
        size_t offset = i->iov_offset;
        size_t size = i->count;
        const struct iovec *iov = i->iov;
        int npages = 0;
        int n;

        for (n = 0; size && n < i->nr_segs; n++, iov++) {
                unsigned long addr = (unsigned long)iov->iov_base + offset;
                size_t len = iov->iov_len - offset;
                offset = 0;
                if (unlikely(!len))     /* empty segment */
                        continue;
                if (len > size)
                        len = size;
                npages += (addr + len + PAGE_SIZE - 1) / PAGE_SIZE
                          - addr / PAGE_SIZE;
                if (npages >= maxpages) /* don't bother going further */
                        return maxpages;
                size -= len;
                offset = 0;
        }
        return min(npages, maxpages);
}

static void memcpy_from_page(char *to, struct page *page, size_t offset, size_t len)
{
        char *from = kmap_atomic(page);
        memcpy(to, from + offset, len);
        kunmap_atomic(from);
}

static void memcpy_to_page(struct page *page, size_t offset, char *from, size_t len)
{
        char *to = kmap_atomic(page);
        memcpy(to + offset, from, len);
        kunmap_atomic(to);
}

static void memzero_page(struct page *page, size_t offset, size_t len)
{
        char *addr = kmap_atomic(page);
        memset(addr + offset, 0, len);
        kunmap_atomic(addr);
}

static size_t copy_to_iter_bvec(void *from, size_t bytes, struct iov_iter *i)
{
        size_t skip, copy, wanted;
        const struct bio_vec *bvec;

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

        if (unlikely(!bytes))
                return 0;

        wanted = bytes;
        bvec = i->bvec;
        skip = i->iov_offset;
        copy = min_t(size_t, bytes, bvec->bv_len - skip);

        memcpy_to_page(bvec->bv_page, skip + bvec->bv_offset, from, copy);
        skip += copy;
        from += copy;
        bytes -= copy;
        while (bytes) {
                bvec++;
                copy = min(bytes, (size_t)bvec->bv_len);
                memcpy_to_page(bvec->bv_page, bvec->bv_offset, from, copy);
                skip = copy;
                from += copy;
                bytes -= copy;
        }
        if (skip == bvec->bv_len) {
                bvec++;
                skip = 0;
        }
        i->count -= wanted - bytes;
        i->nr_segs -= bvec - i->bvec;
        i->bvec = bvec;
        i->iov_offset = skip;
        return wanted - bytes;
}

static size_t copy_from_iter_bvec(void *to, size_t bytes, struct iov_iter *i)
{
        size_t skip, copy, wanted;
        const struct bio_vec *bvec;

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

        if (unlikely(!bytes))
                return 0;

        wanted = bytes;
        bvec = i->bvec;
        skip = i->iov_offset;

        copy = min(bytes, bvec->bv_len - skip);

        memcpy_from_page(to, bvec->bv_page, bvec->bv_offset + skip, copy);

        to += copy;
        skip += copy;
        bytes -= copy;

        while (bytes) {
                bvec++;
                copy = min(bytes, (size_t)bvec->bv_len);
                memcpy_from_page(to, bvec->bv_page, bvec->bv_offset, copy);
                skip = copy;
                to += copy;
                bytes -= copy;
        }
        if (skip == bvec->bv_len) {
                bvec++;
                skip = 0;
        }
        i->count -= wanted;
        i->nr_segs -= bvec - i->bvec;
        i->bvec = bvec;
        i->iov_offset = skip;
        return wanted;
}

static size_t copy_page_to_iter_bvec(struct page *page, size_t offset,
                                        size_t bytes, struct iov_iter *i)
{
        void *kaddr = kmap_atomic(page);
        size_t wanted = copy_to_iter_bvec(kaddr + offset, bytes, i);
        kunmap_atomic(kaddr);
        return wanted;
}

static size_t copy_page_from_iter_bvec(struct page *page, size_t offset,
                                        size_t bytes, struct iov_iter *i)
{
        void *kaddr = kmap_atomic(page);
        size_t wanted = copy_from_iter_bvec(kaddr + offset, bytes, i);
        kunmap_atomic(kaddr);
        return wanted;
}

static size_t zero_bvec(size_t bytes, struct iov_iter *i)
{
        size_t skip, copy, wanted;
        const struct bio_vec *bvec;

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

        if (unlikely(!bytes))
                return 0;

        wanted = bytes;
        bvec = i->bvec;
        skip = i->iov_offset;
        copy = min_t(size_t, bytes, bvec->bv_len - skip);

        memzero_page(bvec->bv_page, skip + bvec->bv_offset, copy);
        skip += copy;
        bytes -= copy;
        while (bytes) {
                bvec++;
                copy = min(bytes, (size_t)bvec->bv_len);
                memzero_page(bvec->bv_page, bvec->bv_offset, copy);
                skip = copy;
                bytes -= copy;
        }
        if (skip == bvec->bv_len) {
                bvec++;
                skip = 0;
        }
        i->count -= wanted - bytes;
        i->nr_segs -= bvec - i->bvec;
        i->bvec = bvec;
        i->iov_offset = skip;
        return wanted - bytes;
}

static size_t copy_from_user_bvec(struct page *page,
                struct iov_iter *i, unsigned long offset, size_t bytes)
{
        char *kaddr;
        size_t left;
        const struct bio_vec *bvec;
        size_t base = i->iov_offset;

        kaddr = kmap_atomic(page);
        for (left = bytes, bvec = i->bvec; left; bvec++, base = 0) {
                size_t copy = min(left, bvec->bv_len - base);
                if (!bvec->bv_len)
                        continue;
                memcpy_from_page(kaddr + offset, bvec->bv_page,
                                 bvec->bv_offset + base, copy);
                offset += copy;
                left -= copy;
        }
        kunmap_atomic(kaddr);
        return bytes;
}

static void advance_bvec(struct iov_iter *i, size_t bytes)
{
        BUG_ON(i->count < bytes);

        if (likely(i->nr_segs == 1)) {
                i->iov_offset += bytes;
                i->count -= bytes;
        } else {
                const struct bio_vec *bvec = i->bvec;
                size_t base = i->iov_offset;
                unsigned long nr_segs = i->nr_segs;

                /*
                 * The !iov->iov_len check ensures we skip over unlikely
                 * zero-length segments (without overruning the iovec).
                 */
                while (bytes || unlikely(i->count && !bvec->bv_len)) {
                        int copy;

                        copy = min(bytes, bvec->bv_len - base);
                        BUG_ON(!i->count || i->count < copy);
                        i->count -= copy;
                        bytes -= copy;
                        base += copy;
                        if (bvec->bv_len == base) {
                                bvec++;
                                nr_segs--;
                                base = 0;
                        }
                }
                i->bvec = bvec;
                i->iov_offset = base;
                i->nr_segs = nr_segs;
        }
}

static unsigned long alignment_bvec(const struct iov_iter *i)
{
        const struct bio_vec *bvec = i->bvec;
        unsigned long res;
        size_t size = i->count;
        size_t n;

        if (!size)
                return 0;

        res = bvec->bv_offset + i->iov_offset;
        n = bvec->bv_len - i->iov_offset;
        if (n >= size)
                return res | size;
        size -= n;
        res |= n;
        while (size > (++bvec)->bv_len) {
                res |= bvec->bv_offset | bvec->bv_len;
                size -= bvec->bv_len;
        }
        res |= bvec->bv_offset | size;
        return res;
}

static ssize_t get_pages_bvec(struct iov_iter *i,
                   struct page **pages, size_t maxsize, unsigned maxpages,
                   size_t *start)
{
        const struct bio_vec *bvec = i->bvec;
        size_t len = bvec->bv_len - i->iov_offset;
        if (len > i->count)
                len = i->count;
        if (len > maxsize)
                len = maxsize;
        /* can't be more than PAGE_SIZE */
        *start = bvec->bv_offset + i->iov_offset;

        get_page(*pages = bvec->bv_page);

        return len;
}

static ssize_t get_pages_alloc_bvec(struct iov_iter *i,
                   struct page ***pages, size_t maxsize,
                   size_t *start)
{
        const struct bio_vec *bvec = i->bvec;
        size_t len = bvec->bv_len - i->iov_offset;
        if (len > i->count)
                len = i->count;
        if (len > maxsize)
                len = maxsize;
        *start = bvec->bv_offset + i->iov_offset;

        *pages = kmalloc(sizeof(struct page *), GFP_KERNEL);
        if (!*pages)
                return -ENOMEM;

        get_page(**pages = bvec->bv_page);

        return len;
}

static int iov_iter_npages_bvec(const struct iov_iter *i, int maxpages)
{
        size_t offset = i->iov_offset;
        size_t size = i->count;
        const struct bio_vec *bvec = i->bvec;
        int npages = 0;
        int n;

        for (n = 0; size && n < i->nr_segs; n++, bvec++) {
                size_t len = bvec->bv_len - offset;
                offset = 0;
                if (unlikely(!len))     /* empty segment */
                        continue;
                if (len > size)
                        len = size;
                npages++;
                if (npages >= maxpages) /* don't bother going further */
                        return maxpages;
                size -= len;
                offset = 0;
        }
        return min(npages, maxpages);
}

size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
{
        if (i->type & ITER_BVEC)
                return copy_page_to_iter_bvec(page, offset, bytes, i);
        else
                return copy_page_to_iter_iovec(page, offset, bytes, i);
}
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 (i->type & ITER_BVEC)
                return copy_page_from_iter_bvec(page, offset, bytes, i);
        else
                return copy_page_from_iter_iovec(page, offset, bytes, i);
}
EXPORT_SYMBOL(copy_page_from_iter);

size_t copy_to_iter(void *addr, size_t bytes, struct iov_iter *i)
{
        if (i->type & ITER_BVEC)
                return copy_to_iter_bvec(addr, bytes, i);
        else
                return copy_to_iter_iovec(addr, bytes, i);
}
EXPORT_SYMBOL(copy_to_iter);

size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
{
        if (i->type & ITER_BVEC)
                return copy_from_iter_bvec(addr, bytes, i);
        else
                return copy_from_iter_iovec(addr, bytes, i);
}
EXPORT_SYMBOL(copy_from_iter);

size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
{
        if (i->type & ITER_BVEC) {
                return zero_bvec(bytes, i);
        } else {
                return zero_iovec(bytes, i);
        }
}
EXPORT_SYMBOL(iov_iter_zero);

size_t iov_iter_copy_from_user_atomic(struct page *page,
                struct iov_iter *i, unsigned long offset, size_t bytes)
{
        if (i->type & ITER_BVEC)
                return copy_from_user_bvec(page, i, offset, bytes);
        else
                return copy_from_user_atomic_iovec(page, i, offset, bytes);
}
EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);

void iov_iter_advance(struct iov_iter *i, size_t size)
{
        if (i->type & ITER_BVEC)
                advance_bvec(i, size);
        else
                advance_iovec(i, size);
}
EXPORT_SYMBOL(iov_iter_advance);

/*
 * 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)
                return i->count;
        else if (i->type & ITER_BVEC)
                return min(i->count, i->bvec->bv_len - i->iov_offset);
        else
                return min(i->count, i->iov->iov_len - i->iov_offset);
}
EXPORT_SYMBOL(iov_iter_single_seg_count);

unsigned long iov_iter_alignment(const struct iov_iter *i)
{
        if (i->type & ITER_BVEC)
                return alignment_bvec(i);
        else
                return alignment_iovec(i);
}
EXPORT_SYMBOL(iov_iter_alignment);

ssize_t iov_iter_get_pages(struct iov_iter *i,
                   struct page **pages, size_t maxsize, unsigned maxpages,
                   size_t *start)
{
        if (i->type & ITER_BVEC)
                return get_pages_bvec(i, pages, maxsize, maxpages, start);
        else
                return get_pages_iovec(i, pages, maxsize, maxpages, start);
}
EXPORT_SYMBOL(iov_iter_get_pages);

ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
                   struct page ***pages, size_t maxsize,
                   size_t *start)
{
        if (i->type & ITER_BVEC)
                return get_pages_alloc_bvec(i, pages, maxsize, start);
        else
                return get_pages_alloc_iovec(i, pages, maxsize, start);
}
EXPORT_SYMBOL(iov_iter_get_pages_alloc);

int iov_iter_npages(const struct iov_iter *i, int maxpages)
{
        if (i->type & ITER_BVEC)
                return iov_iter_npages_bvec(i, maxpages);
        else
                return iov_iter_npages_iovec(i, maxpages);
}
EXPORT_SYMBOL(iov_iter_npages);