/*
 * linux/net/sunrpc/xdr.c
 *
 * Generic XDR support.
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/pagemap.h>
#include <linux/errno.h>
#include <linux/sunrpc/xdr.h>
#include <linux/sunrpc/msg_prot.h>

/*
 * XDR functions for basic NFS types
 */
__be32 *
xdr_encode_netobj(__be32 *p, const struct xdr_netobj *obj)
{
        unsigned int    quadlen = XDR_QUADLEN(obj->len);

        p[quadlen] = 0;         /* zero trailing bytes */
        *p++ = cpu_to_be32(obj->len);
        memcpy(p, obj->data, obj->len);
        return p + XDR_QUADLEN(obj->len);
}
EXPORT_SYMBOL_GPL(xdr_encode_netobj);

__be32 *
xdr_decode_netobj(__be32 *p, struct xdr_netobj *obj)
{
        unsigned int    len;

        if ((len = be32_to_cpu(*p++)) > XDR_MAX_NETOBJ)
                return NULL;
        obj->len  = len;
        obj->data = (u8 *) p;
        return p + XDR_QUADLEN(len);
}
EXPORT_SYMBOL_GPL(xdr_decode_netobj);

/**
 * xdr_encode_opaque_fixed - Encode fixed length opaque data
 * @p: pointer to current position in XDR buffer.
 * @ptr: pointer to data to encode (or NULL)
 * @nbytes: size of data.
 *
 * Copy the array of data of length nbytes at ptr to the XDR buffer
 * at position p, then align to the next 32-bit boundary by padding
 * with zero bytes (see RFC1832).
 * Note: if ptr is NULL, only the padding is performed.
 *
 * Returns the updated current XDR buffer position
 *
 */
__be32 *xdr_encode_opaque_fixed(__be32 *p, const void *ptr, unsigned int nbytes)
{
        if (likely(nbytes != 0)) {
                unsigned int quadlen = XDR_QUADLEN(nbytes);
                unsigned int padding = (quadlen << 2) - nbytes;

                if (ptr != NULL)
                        memcpy(p, ptr, nbytes);
                if (padding != 0)
                        memset((char *)p + nbytes, 0, padding);
                p += quadlen;
        }
        return p;
}
EXPORT_SYMBOL_GPL(xdr_encode_opaque_fixed);

/**
 * xdr_encode_opaque - Encode variable length opaque data
 * @p: pointer to current position in XDR buffer.
 * @ptr: pointer to data to encode (or NULL)
 * @nbytes: size of data.
 *
 * Returns the updated current XDR buffer position
 */
__be32 *xdr_encode_opaque(__be32 *p, const void *ptr, unsigned int nbytes)
{
        *p++ = cpu_to_be32(nbytes);
        return xdr_encode_opaque_fixed(p, ptr, nbytes);
}
EXPORT_SYMBOL_GPL(xdr_encode_opaque);

__be32 *
xdr_encode_string(__be32 *p, const char *string)
{
        return xdr_encode_array(p, string, strlen(string));
}
EXPORT_SYMBOL_GPL(xdr_encode_string);

__be32 *
xdr_decode_string_inplace(__be32 *p, char **sp,
                          unsigned int *lenp, unsigned int maxlen)
{
        u32 len;

        len = be32_to_cpu(*p++);
        if (len > maxlen)
                return NULL;
        *lenp = len;
        *sp = (char *) p;
        return p + XDR_QUADLEN(len);
}
EXPORT_SYMBOL_GPL(xdr_decode_string_inplace);

/**
 * xdr_terminate_string - '\0'-terminate a string residing in an xdr_buf
 * @buf: XDR buffer where string resides
 * @len: length of string, in bytes
 *
 */
void
xdr_terminate_string(struct xdr_buf *buf, const u32 len)
{
        char *kaddr;

        kaddr = kmap_atomic(buf->pages[0]);
        kaddr[buf->page_base + len] = '\0';
        kunmap_atomic(kaddr);
}
EXPORT_SYMBOL_GPL(xdr_terminate_string);

void
xdr_inline_pages(struct xdr_buf *xdr, unsigned int offset,
                 struct page **pages, unsigned int base, unsigned int len)
{
        struct kvec *head = xdr->head;
        struct kvec *tail = xdr->tail;
        char *buf = (char *)head->iov_base;
        unsigned int buflen = head->iov_len;

        head->iov_len  = offset;

        xdr->pages = pages;
        xdr->page_base = base;
        xdr->page_len = len;

        tail->iov_base = buf + offset;
        tail->iov_len = buflen - offset;

        xdr->buflen += len;
}
EXPORT_SYMBOL_GPL(xdr_inline_pages);

/*
 * Helper routines for doing 'memmove' like operations on a struct xdr_buf
 */

/**
 * _shift_data_right_pages
 * @pages: vector of pages containing both the source and dest memory area.
 * @pgto_base: page vector address of destination
 * @pgfrom_base: page vector address of source
 * @len: number of bytes to copy
 *
 * Note: the addresses pgto_base and pgfrom_base are both calculated in
 *       the same way:
 *            if a memory area starts at byte 'base' in page 'pages[i]',
 *            then its address is given as (i << PAGE_CACHE_SHIFT) + base
 * Also note: pgfrom_base must be < pgto_base, but the memory areas
 *      they point to may overlap.
 */
static void
_shift_data_right_pages(struct page **pages, size_t pgto_base,
                size_t pgfrom_base, size_t len)
{
        struct page **pgfrom, **pgto;
        char *vfrom, *vto;
        size_t copy;

        BUG_ON(pgto_base <= pgfrom_base);

        pgto_base += len;
        pgfrom_base += len;

        pgto = pages + (pgto_base >> PAGE_CACHE_SHIFT);
        pgfrom = pages + (pgfrom_base >> PAGE_CACHE_SHIFT);

        pgto_base &= ~PAGE_CACHE_MASK;
        pgfrom_base &= ~PAGE_CACHE_MASK;

        do {
                /* Are any pointers crossing a page boundary? */
                if (pgto_base == 0) {
                        pgto_base = PAGE_CACHE_SIZE;
                        pgto--;
                }
                if (pgfrom_base == 0) {
                        pgfrom_base = PAGE_CACHE_SIZE;
                        pgfrom--;
                }

                copy = len;
                if (copy > pgto_base)
                        copy = pgto_base;
                if (copy > pgfrom_base)
                        copy = pgfrom_base;
                pgto_base -= copy;
                pgfrom_base -= copy;

                vto = kmap_atomic(*pgto);
                if (*pgto != *pgfrom) {
                        vfrom = kmap_atomic(*pgfrom);
                        memcpy(vto + pgto_base, vfrom + pgfrom_base, copy);
                        kunmap_atomic(vfrom);
                } else
                        memmove(vto + pgto_base, vto + pgfrom_base, copy);
                flush_dcache_page(*pgto);
                kunmap_atomic(vto);

        } while ((len -= copy) != 0);
}

/**
 * _copy_to_pages
 * @pages: array of pages
 * @pgbase: page vector address of destination
 * @p: pointer to source data
 * @len: length
 *
 * Copies data from an arbitrary memory location into an array of pages
 * The copy is assumed to be non-overlapping.
 */
static void
_copy_to_pages(struct page **pages, size_t pgbase, const char *p, size_t len)
{
        struct page **pgto;
        char *vto;
        size_t copy;

        pgto = pages + (pgbase >> PAGE_CACHE_SHIFT);
        pgbase &= ~PAGE_CACHE_MASK;

        for (;;) {
                copy = PAGE_CACHE_SIZE - pgbase;
                if (copy > len)
                        copy = len;

                vto = kmap_atomic(*pgto);
                memcpy(vto + pgbase, p, copy);
                kunmap_atomic(vto);

                len -= copy;
                if (len == 0)
                        break;

                pgbase += copy;
                if (pgbase == PAGE_CACHE_SIZE) {
                        flush_dcache_page(*pgto);
                        pgbase = 0;
                        pgto++;
                }
                p += copy;
        }
        flush_dcache_page(*pgto);
}

/**
 * _copy_from_pages
 * @p: pointer to destination
 * @pages: array of pages
 * @pgbase: offset of source data
 * @len: length
 *
 * Copies data into an arbitrary memory location from an array of pages
 * The copy is assumed to be non-overlapping.
 */
void
_copy_from_pages(char *p, struct page **pages, size_t pgbase, size_t len)
{
        struct page **pgfrom;
        char *vfrom;
        size_t copy;

        pgfrom = pages + (pgbase >> PAGE_CACHE_SHIFT);
        pgbase &= ~PAGE_CACHE_MASK;

        do {
                copy = PAGE_CACHE_SIZE - pgbase;
                if (copy > len)
                        copy = len;

                vfrom = kmap_atomic(*pgfrom);
                memcpy(p, vfrom + pgbase, copy);
                kunmap_atomic(vfrom);

                pgbase += copy;
                if (pgbase == PAGE_CACHE_SIZE) {
                        pgbase = 0;
                        pgfrom++;
                }
                p += copy;

        } while ((len -= copy) != 0);
}
EXPORT_SYMBOL_GPL(_copy_from_pages);

/**
 * xdr_shrink_bufhead
 * @buf: xdr_buf
 * @len: bytes to remove from buf->head[0]
 *
 * Shrinks XDR buffer's header kvec buf->head[0] by
 * 'len' bytes. The extra data is not lost, but is instead
 * moved into the inlined pages and/or the tail.
 */
static void
xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
{
        struct kvec *head, *tail;
        size_t copy, offs;
        unsigned int pglen = buf->page_len;

        tail = buf->tail;
        head = buf->head;

        WARN_ON_ONCE(len > head->iov_len);
        if (len > head->iov_len)
                len = head->iov_len;

        /* Shift the tail first */
        if (tail->iov_len != 0) {
                if (tail->iov_len > len) {
                        copy = tail->iov_len - len;
                        memmove((char *)tail->iov_base + len,
                                        tail->iov_base, copy);
                }
                /* Copy from the inlined pages into the tail */
                copy = len;
                if (copy > pglen)
                        copy = pglen;
                offs = len - copy;
                if (offs >= tail->iov_len)
                        copy = 0;
                else if (copy > tail->iov_len - offs)
                        copy = tail->iov_len - offs;
                if (copy != 0)
                        _copy_from_pages((char *)tail->iov_base + offs,
                                        buf->pages,
                                        buf->page_base + pglen + offs - len,
                                        copy);
                /* Do we also need to copy data from the head into the tail ? */
                if (len > pglen) {
                        offs = copy = len - pglen;
                        if (copy > tail->iov_len)
                                copy = tail->iov_len;
                        memcpy(tail->iov_base,
                                        (char *)head->iov_base +
                                        head->iov_len - offs,
                                        copy);
                }
        }
        /* Now handle pages */
        if (pglen != 0) {
                if (pglen > len)
                        _shift_data_right_pages(buf->pages,
                                        buf->page_base + len,
                                        buf->page_base,
                                        pglen - len);
                copy = len;
                if (len > pglen)
                        copy = pglen;
                _copy_to_pages(buf->pages, buf->page_base,
                                (char *)head->iov_base + head->iov_len - len,
                                copy);
        }
        head->iov_len -= len;
        buf->buflen -= len;
        /* Have we truncated the message? */
        if (buf->len > buf->buflen)
                buf->len = buf->buflen;
}

/**
 * xdr_shrink_pagelen
 * @buf: xdr_buf
 * @len: bytes to remove from buf->pages
 *
 * Shrinks XDR buffer's page array buf->pages by
 * 'len' bytes. The extra data is not lost, but is instead
 * moved into the tail.
 */
static void
xdr_shrink_pagelen(struct xdr_buf *buf, size_t len)
{
        struct kvec *tail;
        size_t copy;
        unsigned int pglen = buf->page_len;
        unsigned int tailbuf_len;

        tail = buf->tail;
        BUG_ON (len > pglen);

        tailbuf_len = buf->buflen - buf->head->iov_len - buf->page_len;

        /* Shift the tail first */
        if (tailbuf_len != 0) {
                unsigned int free_space = tailbuf_len - tail->iov_len;

                if (len < free_space)
                        free_space = len;
                tail->iov_len += free_space;

                copy = len;
                if (tail->iov_len > len) {
                        char *p = (char *)tail->iov_base + len;
                        memmove(p, tail->iov_base, tail->iov_len - len);
                } else
                        copy = tail->iov_len;
                /* Copy from the inlined pages into the tail */
                _copy_from_pages((char *)tail->iov_base,
                                buf->pages, buf->page_base + pglen - len,
                                copy);
        }
        buf->page_len -= len;
        buf->buflen -= len;
        /* Have we truncated the message? */
        if (buf->len > buf->buflen)
                buf->len = buf->buflen;
}

void
xdr_shift_buf(struct xdr_buf *buf, size_t len)
{
        xdr_shrink_bufhead(buf, len);
}
EXPORT_SYMBOL_GPL(xdr_shift_buf);

/**
 * xdr_stream_pos - Return the current offset from the start of the xdr_stream
 * @xdr: pointer to struct xdr_stream
 */
unsigned int xdr_stream_pos(const struct xdr_stream *xdr)
{
        return (unsigned int)(XDR_QUADLEN(xdr->buf->len) - xdr->nwords) << 2;
}
EXPORT_SYMBOL_GPL(xdr_stream_pos);

/**
 * xdr_init_encode - Initialize a struct xdr_stream for sending data.
 * @xdr: pointer to xdr_stream struct
 * @buf: pointer to XDR buffer in which to encode data
 * @p: current pointer inside XDR buffer
 *
 * Note: at the moment the RPC client only passes the length of our
 *       scratch buffer in the xdr_buf's header kvec. Previously this
 *       meant we needed to call xdr_adjust_iovec() after encoding the
 *       data. With the new scheme, the xdr_stream manages the details
 *       of the buffer length, and takes care of adjusting the kvec
 *       length for us.
 */
void xdr_init_encode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32 *p)
{
        struct kvec *iov = buf->head;
        int scratch_len = buf->buflen - buf->page_len - buf->tail[0].iov_len;

        BUG_ON(scratch_len < 0);
        xdr->buf = buf;
        xdr->iov = iov;
        xdr->p = (__be32 *)((char *)iov->iov_base + iov->iov_len);
        xdr->end = (__be32 *)((char *)iov->iov_base + scratch_len);
        BUG_ON(iov->iov_len > scratch_len);

        if (p != xdr->p && p != NULL) {
                size_t len;

                BUG_ON(p < xdr->p || p > xdr->end);
                len = (char *)p - (char *)xdr->p;
                xdr->p = p;
                buf->len += len;
                iov->iov_len += len;
        }
}
EXPORT_SYMBOL_GPL(xdr_init_encode);

/**
 * xdr_reserve_space - Reserve buffer space for sending
 * @xdr: pointer to xdr_stream
 * @nbytes: number of bytes to reserve
 *
 * Checks that we have enough buffer space to encode 'nbytes' more
 * bytes of data. If so, update the total xdr_buf length, and
 * adjust the length of the current kvec.
 */
__be32 * xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes)
{
        __be32 *p = xdr->p;
        __be32 *q;

        /* align nbytes on the next 32-bit boundary */
        nbytes += 3;
        nbytes &= ~3;
        q = p + (nbytes >> 2);
        if (unlikely(q > xdr->end || q < p))
                return NULL;
        xdr->p = q;
        xdr->iov->iov_len += nbytes;
        xdr->buf->len += nbytes;
        return p;
}
EXPORT_SYMBOL_GPL(xdr_reserve_space);

/**
 * xdr_write_pages - Insert a list of pages into an XDR buffer for sending
 * @xdr: pointer to xdr_stream
 * @pages: list of pages
 * @base: offset of first byte
 * @len: length of data in bytes
 *
 */
void xdr_write_pages(struct xdr_stream *xdr, struct page **pages, unsigned int base,
                 unsigned int len)
{
        struct xdr_buf *buf = xdr->buf;
        struct kvec *iov = buf->tail;
        buf->pages = pages;
        buf->page_base = base;
        buf->page_len = len;

        iov->iov_base = (char *)xdr->p;
        iov->iov_len  = 0;
        xdr->iov = iov;

        if (len & 3) {
                unsigned int pad = 4 - (len & 3);

                BUG_ON(xdr->p >= xdr->end);
                iov->iov_base = (char *)xdr->p + (len & 3);
                iov->iov_len  += pad;
                len += pad;
                *xdr->p++ = 0;
        }
        buf->buflen += len;
        buf->len += len;
}
EXPORT_SYMBOL_GPL(xdr_write_pages);

static void xdr_set_iov(struct xdr_stream *xdr, struct kvec *iov,
                unsigned int len)
{
        if (len > iov->iov_len)
                len = iov->iov_len;
        xdr->p = (__be32*)iov->iov_base;
        xdr->end = (__be32*)(iov->iov_base + len);
        xdr->iov = iov;
        xdr->page_ptr = NULL;
}

static int xdr_set_page_base(struct xdr_stream *xdr,
                unsigned int base, unsigned int len)
{
        unsigned int pgnr;
        unsigned int maxlen;
        unsigned int pgoff;
        unsigned int pgend;
        void *kaddr;

        maxlen = xdr->buf->page_len;
        if (base >= maxlen)
                return -EINVAL;
        maxlen -= base;
        if (len > maxlen)
                len = maxlen;

        base += xdr->buf->page_base;

        pgnr = base >> PAGE_SHIFT;
        xdr->page_ptr = &xdr->buf->pages[pgnr];
        kaddr = page_address(*xdr->page_ptr);

        pgoff = base & ~PAGE_MASK;
        xdr->p = (__be32*)(kaddr + pgoff);

        pgend = pgoff + len;
        if (pgend > PAGE_SIZE)
                pgend = PAGE_SIZE;
        xdr->end = (__be32*)(kaddr + pgend);
        xdr->iov = NULL;
        return 0;
}

static void xdr_set_next_page(struct xdr_stream *xdr)
{
        unsigned int newbase;

        newbase = (1 + xdr->page_ptr - xdr->buf->pages) << PAGE_SHIFT;
        newbase -= xdr->buf->page_base;

        if (xdr_set_page_base(xdr, newbase, PAGE_SIZE) < 0)
                xdr_set_iov(xdr, xdr->buf->tail, xdr->buf->len);
}

static bool xdr_set_next_buffer(struct xdr_stream *xdr)
{
        if (xdr->page_ptr != NULL)
                xdr_set_next_page(xdr);
        else if (xdr->iov == xdr->buf->head) {
                if (xdr_set_page_base(xdr, 0, PAGE_SIZE) < 0)
                        xdr_set_iov(xdr, xdr->buf->tail, xdr->buf->len);
        }
        return xdr->p != xdr->end;
}

/**
 * xdr_init_decode - Initialize an xdr_stream for decoding data.
 * @xdr: pointer to xdr_stream struct
 * @buf: pointer to XDR buffer from which to decode data
 * @p: current pointer inside XDR buffer
 */
void xdr_init_decode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32 *p)
{
        xdr->buf = buf;
        xdr->scratch.iov_base = NULL;
        xdr->scratch.iov_len = 0;
        xdr->nwords = XDR_QUADLEN(buf->len);
        if (buf->head[0].iov_len != 0)
                xdr_set_iov(xdr, buf->head, buf->len);
        else if (buf->page_len != 0)
                xdr_set_page_base(xdr, 0, buf->len);
        if (p != NULL && p > xdr->p && xdr->end >= p) {
                xdr->nwords -= p - xdr->p;
                xdr->p = p;
        }
}
EXPORT_SYMBOL_GPL(xdr_init_decode);

/**
 * xdr_init_decode - Initialize an xdr_stream for decoding data.
 * @xdr: pointer to xdr_stream struct
 * @buf: pointer to XDR buffer from which to decode data
 * @pages: list of pages to decode into
 * @len: length in bytes of buffer in pages
 */
void xdr_init_decode_pages(struct xdr_stream *xdr, struct xdr_buf *buf,
                           struct page **pages, unsigned int len)
{
        memset(buf, 0, sizeof(*buf));
        buf->pages =  pages;
        buf->page_len =  len;
        buf->buflen =  len;
        buf->len = len;
        xdr_init_decode(xdr, buf, NULL);
}
EXPORT_SYMBOL_GPL(xdr_init_decode_pages);

static __be32 * __xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
{
        unsigned int nwords = XDR_QUADLEN(nbytes);
        __be32 *p = xdr->p;
        __be32 *q = p + nwords;

        if (unlikely(nwords > xdr->nwords || q > xdr->end || q < p))
                return NULL;
        xdr->p = q;
        xdr->nwords -= nwords;
        return p;
}

/**
 * xdr_set_scratch_buffer - Attach a scratch buffer for decoding data.
 * @xdr: pointer to xdr_stream struct
 * @buf: pointer to an empty buffer
 * @buflen: size of 'buf'
 *
 * The scratch buffer is used when decoding from an array of pages.
 * If an xdr_inline_decode() call spans across page boundaries, then
 * we copy the data into the scratch buffer in order to allow linear
 * access.
 */
void xdr_set_scratch_buffer(struct xdr_stream *xdr, void *buf, size_t buflen)
{
        xdr->scratch.iov_base = buf;
        xdr->scratch.iov_len = buflen;
}
EXPORT_SYMBOL_GPL(xdr_set_scratch_buffer);

static __be32 *xdr_copy_to_scratch(struct xdr_stream *xdr, size_t nbytes)
{
        __be32 *p;
        void *cpdest = xdr->scratch.iov_base;
        size_t cplen = (char *)xdr->end - (char *)xdr->p;

        if (nbytes > xdr->scratch.iov_len)
                return NULL;
        memcpy(cpdest, xdr->p, cplen);
        cpdest += cplen;
        nbytes -= cplen;
        if (!xdr_set_next_buffer(xdr))
                return NULL;
        p = __xdr_inline_decode(xdr, nbytes);
        if (p == NULL)
                return NULL;
        memcpy(cpdest, p, nbytes);
        return xdr->scratch.iov_base;
}

/**
 * xdr_inline_decode - Retrieve XDR data to decode
 * @xdr: pointer to xdr_stream struct
 * @nbytes: number of bytes of data to decode
 *
 * Check if the input buffer is long enough to enable us to decode
 * 'nbytes' more bytes of data starting at the current position.
 * If so return the current pointer, then update the current
 * pointer position.
 */
__be32 * xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
{
        __be32 *p;

        if (nbytes == 0)
                return xdr->p;
        if (xdr->p == xdr->end && !xdr_set_next_buffer(xdr))
                return NULL;
        p = __xdr_inline_decode(xdr, nbytes);
        if (p != NULL)
                return p;
        return xdr_copy_to_scratch(xdr, nbytes);
}
EXPORT_SYMBOL_GPL(xdr_inline_decode);

static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
{
        struct xdr_buf *buf = xdr->buf;
        struct kvec *iov;
        unsigned int nwords = XDR_QUADLEN(len);
        unsigned int cur = xdr_stream_pos(xdr);

        if (xdr->nwords == 0)
                return 0;
        /* Realign pages to current pointer position */
        iov  = buf->head;
        if (iov->iov_len > cur) {
                xdr_shrink_bufhead(buf, iov->iov_len - cur);
                xdr->nwords = XDR_QUADLEN(buf->len - cur);
        }

        if (nwords > xdr->nwords) {
                nwords = xdr->nwords;
                len = nwords << 2;
        }
        if (buf->page_len <= len)
                len = buf->page_len;
        else if (nwords < xdr->nwords) {
                /* Truncate page data and move it into the tail */
                xdr_shrink_pagelen(buf, buf->page_len - len);
                xdr->nwords = XDR_QUADLEN(buf->len - cur);
        }
        return len;
}

/**
 * xdr_read_pages - Ensure page-based XDR data to decode is aligned at current pointer position
 * @xdr: pointer to xdr_stream struct
 * @len: number of bytes of page data
 *
 * Moves data beyond the current pointer position from the XDR head[] buffer
 * into the page list. Any data that lies beyond current position + "len"
 * bytes is moved into the XDR tail[].
 *
 * Returns the number of XDR encoded bytes now contained in the pages
 */
unsigned int xdr_read_pages(struct xdr_stream *xdr, unsigned int len)
{
        struct xdr_buf *buf = xdr->buf;
        struct kvec *iov;
        unsigned int nwords;
        unsigned int end;
        unsigned int padding;

        len = xdr_align_pages(xdr, len);
        if (len == 0)
                return 0;
        nwords = XDR_QUADLEN(len);
        padding = (nwords << 2) - len;
        xdr->iov = iov = buf->tail;
        /* Compute remaining message length.  */
        end = ((xdr->nwords - nwords) << 2) + padding;
        if (end > iov->iov_len)
                end = iov->iov_len;

        /*
         * Position current pointer at beginning of tail, and
         * set remaining message length.
         */
        xdr->p = (__be32 *)((char *)iov->iov_base + padding);
        xdr->end = (__be32 *)((char *)iov->iov_base + end);
        xdr->page_ptr = NULL;
        xdr->nwords = XDR_QUADLEN(end - padding);
        return len;
}
EXPORT_SYMBOL_GPL(xdr_read_pages);

/**
 * xdr_enter_page - decode data from the XDR page
 * @xdr: pointer to xdr_stream struct
 * @len: number of bytes of page data
 *
 * Moves data beyond the current pointer position from the XDR head[] buffer
 * into the page list. Any data that lies beyond current position + "len"
 * bytes is moved into the XDR tail[]. The current pointer is then
 * repositioned at the beginning of the first XDR page.
 */
void xdr_enter_page(struct xdr_stream *xdr, unsigned int len)
{
        len = xdr_align_pages(xdr, len);
        /*
         * Position current pointer at beginning of tail, and
         * set remaining message length.
         */
        if (len != 0)
                xdr_set_page_base(xdr, 0, len);
}
EXPORT_SYMBOL_GPL(xdr_enter_page);

static struct kvec empty_iov = {.iov_base = NULL, .iov_len = 0};

void
xdr_buf_from_iov(struct kvec *iov, struct xdr_buf *buf)
{
        buf->head[0] = *iov;
        buf->tail[0] = empty_iov;
        buf->page_len = 0;
        buf->buflen = buf->len = iov->iov_len;
}
EXPORT_SYMBOL_GPL(xdr_buf_from_iov);

/* Sets subbuf to the portion of buf of length len beginning base bytes
 * from the start of buf. Returns -1 if base of length are out of bounds. */
int
xdr_buf_subsegment(struct xdr_buf *buf, struct xdr_buf *subbuf,
                        unsigned int base, unsigned int len)
{
        subbuf->buflen = subbuf->len = len;
        if (base < buf->head[0].iov_len) {
                subbuf->head[0].iov_base = buf->head[0].iov_base + base;
                subbuf->head[0].iov_len = min_t(unsigned int, len,
                                                buf->head[0].iov_len - base);
                len -= subbuf->head[0].iov_len;
                base = 0;
        } else {
                subbuf->head[0].iov_base = NULL;
                subbuf->head[0].iov_len = 0;
                base -= buf->head[0].iov_len;
        }

        if (base < buf->page_len) {
                subbuf->page_len = min(buf->page_len - base, len);
                base += buf->page_base;
                subbuf->page_base = base & ~PAGE_CACHE_MASK;
                subbuf->pages = &buf->pages[base >> PAGE_CACHE_SHIFT];
                len -= subbuf->page_len;
                base = 0;
        } else {
                base -= buf->page_len;
                subbuf->page_len = 0;
        }

        if (base < buf->tail[0].iov_len) {
                subbuf->tail[0].iov_base = buf->tail[0].iov_base + base;
                subbuf->tail[0].iov_len = min_t(unsigned int, len,
                                                buf->tail[0].iov_len - base);
                len -= subbuf->tail[0].iov_len;
                base = 0;
        } else {
                subbuf->tail[0].iov_base = NULL;
                subbuf->tail[0].iov_len = 0;
                base -= buf->tail[0].iov_len;
        }

        if (base || len)
                return -1;
        return 0;
}
EXPORT_SYMBOL_GPL(xdr_buf_subsegment);

/**
 * xdr_buf_trim - lop at most "len" bytes off the end of "buf"
 * @buf: buf to be trimmed
 * @len: number of bytes to reduce "buf" by
 *
 * Trim an xdr_buf by the given number of bytes by fixing up the lengths. Note
 * that it's possible that we'll trim less than that amount if the xdr_buf is
 * too small, or if (for instance) it's all in the head and the parser has
 * already read too far into it.
 */
void xdr_buf_trim(struct xdr_buf *buf, unsigned int len)
{
        size_t cur;
        unsigned int trim = len;

        if (buf->tail[0].iov_len) {
                cur = min_t(size_t, buf->tail[0].iov_len, trim);
                buf->tail[0].iov_len -= cur;
                trim -= cur;
                if (!trim)
                        goto fix_len;
        }

        if (buf->page_len) {
                cur = min_t(unsigned int, buf->page_len, trim);
                buf->page_len -= cur;
                trim -= cur;
                if (!trim)
                        goto fix_len;
        }

        if (buf->head[0].iov_len) {
                cur = min_t(size_t, buf->head[0].iov_len, trim);
                buf->head[0].iov_len -= cur;
                trim -= cur;
        }
fix_len:
        buf->len -= (len - trim);
}
EXPORT_SYMBOL_GPL(xdr_buf_trim);

static void __read_bytes_from_xdr_buf(struct xdr_buf *subbuf, void *obj, unsigned int len)
{
        unsigned int this_len;

        this_len = min_t(unsigned int, len, subbuf->head[0].iov_len);
        memcpy(obj, subbuf->head[0].iov_base, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->page_len);
        if (this_len)
                _copy_from_pages(obj, subbuf->pages, subbuf->page_base, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->tail[0].iov_len);
        memcpy(obj, subbuf->tail[0].iov_base, this_len);
}

/* obj is assumed to point to allocated memory of size at least len: */
int read_bytes_from_xdr_buf(struct xdr_buf *buf, unsigned int base, void *obj, unsigned int len)
{
        struct xdr_buf subbuf;
        int status;

        status = xdr_buf_subsegment(buf, &subbuf, base, len);
        if (status != 0)
                return status;
        __read_bytes_from_xdr_buf(&subbuf, obj, len);
        return 0;
}
EXPORT_SYMBOL_GPL(read_bytes_from_xdr_buf);

static void __write_bytes_to_xdr_buf(struct xdr_buf *subbuf, void *obj, unsigned int len)
{
        unsigned int this_len;

        this_len = min_t(unsigned int, len, subbuf->head[0].iov_len);
        memcpy(subbuf->head[0].iov_base, obj, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->page_len);
        if (this_len)
                _copy_to_pages(subbuf->pages, subbuf->page_base, obj, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->tail[0].iov_len);
        memcpy(subbuf->tail[0].iov_base, obj, this_len);
}

/* obj is assumed to point to allocated memory of size at least len: */
int write_bytes_to_xdr_buf(struct xdr_buf *buf, unsigned int base, void *obj, unsigned int len)
{
        struct xdr_buf subbuf;
        int status;

        status = xdr_buf_subsegment(buf, &subbuf, base, len);
        if (status != 0)
                return status;
        __write_bytes_to_xdr_buf(&subbuf, obj, len);
        return 0;
}
EXPORT_SYMBOL_GPL(write_bytes_to_xdr_buf);

int
xdr_decode_word(struct xdr_buf *buf, unsigned int base, u32 *obj)
{
        __be32  raw;
        int     status;

        status = read_bytes_from_xdr_buf(buf, base, &raw, sizeof(*obj));
        if (status)
                return status;
        *obj = be32_to_cpu(raw);
        return 0;
}
EXPORT_SYMBOL_GPL(xdr_decode_word);

int
xdr_encode_word(struct xdr_buf *buf, unsigned int base, u32 obj)
{
        __be32  raw = cpu_to_be32(obj);

        return write_bytes_to_xdr_buf(buf, base, &raw, sizeof(obj));
}
EXPORT_SYMBOL_GPL(xdr_encode_word);

/* If the netobj starting offset bytes from the start of xdr_buf is contained
 * entirely in the head or the tail, set object to point to it; otherwise
 * try to find space for it at the end of the tail, copy it there, and
 * set obj to point to it. */
int xdr_buf_read_netobj(struct xdr_buf *buf, struct xdr_netobj *obj, unsigned int offset)
{
        struct xdr_buf subbuf;

        if (xdr_decode_word(buf, offset, &obj->len))
                return -EFAULT;
        if (xdr_buf_subsegment(buf, &subbuf, offset + 4, obj->len))
                return -EFAULT;

        /* Is the obj contained entirely in the head? */
        obj->data = subbuf.head[0].iov_base;
        if (subbuf.head[0].iov_len == obj->len)
                return 0;
        /* ..or is the obj contained entirely in the tail? */
        obj->data = subbuf.tail[0].iov_base;
        if (subbuf.tail[0].iov_len == obj->len)
                return 0;

        /* use end of tail as storage for obj:
         * (We don't copy to the beginning because then we'd have
         * to worry about doing a potentially overlapping copy.
         * This assumes the object is at most half the length of the
         * tail.) */
        if (obj->len > buf->buflen - buf->len)
                return -ENOMEM;
        if (buf->tail[0].iov_len != 0)
                obj->data = buf->tail[0].iov_base + buf->tail[0].iov_len;
        else
                obj->data = buf->head[0].iov_base + buf->head[0].iov_len;
        __read_bytes_from_xdr_buf(&subbuf, obj->data, obj->len);
        return 0;
}
EXPORT_SYMBOL_GPL(xdr_buf_read_netobj);

/* Returns 0 on success, or else a negative error code. */
static int
xdr_xcode_array2(struct xdr_buf *buf, unsigned int base,
                 struct xdr_array2_desc *desc, int encode)
{
        char *elem = NULL, *c;
        unsigned int copied = 0, todo, avail_here;
        struct page **ppages = NULL;
        int err;

        if (encode) {
                if (xdr_encode_word(buf, base, desc->array_len) != 0)
                        return -EINVAL;
        } else {
                if (xdr_decode_word(buf, base, &desc->array_len) != 0 ||
                    desc->array_len > desc->array_maxlen ||
                    (unsigned long) base + 4 + desc->array_len *
                                    desc->elem_size > buf->len)
                        return -EINVAL;
        }
        base += 4;

        if (!desc->xcode)
                return 0;

        todo = desc->array_len * desc->elem_size;

        /* process head */
        if (todo && base < buf->head->iov_len) {
                c = buf->head->iov_base + base;
                avail_here = min_t(unsigned int, todo,
                                   buf->head->iov_len - base);
                todo -= avail_here;

                while (avail_here >= desc->elem_size) {
                        err = desc->xcode(desc, c);
                        if (err)
                                goto out;
                        c += desc->elem_size;
                        avail_here -= desc->elem_size;
                }
                if (avail_here) {
                        if (!elem) {
                                elem = kmalloc(desc->elem_size, GFP_KERNEL);
                                err = -ENOMEM;
                                if (!elem)
                                        goto out;
                        }
                        if (encode) {
                                err = desc->xcode(desc, elem);
                                if (err)
                                        goto out;
                                memcpy(c, elem, avail_here);
                        } else
                                memcpy(elem, c, avail_here);
                        copied = avail_here;
                }
                base = buf->head->iov_len;  /* align to start of pages */
        }

        /* process pages array */
        base -= buf->head->iov_len;
        if (todo && base < buf->page_len) {
                unsigned int avail_page;

                avail_here = min(todo, buf->page_len - base);
                todo -= avail_here;

                base += buf->page_base;
                ppages = buf->pages + (base >> PAGE_CACHE_SHIFT);
                base &= ~PAGE_CACHE_MASK;
                avail_page = min_t(unsigned int, PAGE_CACHE_SIZE - base,
                                        avail_here);
                c = kmap(*ppages) + base;

                while (avail_here) {
                        avail_here -= avail_page;
                        if (copied || avail_page < desc->elem_size) {
                                unsigned int l = min(avail_page,
                                        desc->elem_size - copied);
                                if (!elem) {
                                        elem = kmalloc(desc->elem_size,
                                                       GFP_KERNEL);
                                        err = -ENOMEM;
                                        if (!elem)
                                                goto out;
                                }
                                if (encode) {
                                        if (!copied) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                        }
                                        memcpy(c, elem + copied, l);
                                        copied += l;
                                        if (copied == desc->elem_size)
                                                copied = 0;
                                } else {
                                        memcpy(elem + copied, c, l);
                                        copied += l;
                                        if (copied == desc->elem_size) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                                copied = 0;
                                        }
                                }
                                avail_page -= l;
                                c += l;
                        }
                        while (avail_page >= desc->elem_size) {
                                err = desc->xcode(desc, c);
                                if (err)
                                        goto out;
                                c += desc->elem_size;
                                avail_page -= desc->elem_size;
                        }
                        if (avail_page) {
                                unsigned int l = min(avail_page,
                                            desc->elem_size - copied);
                                if (!elem) {
                                        elem = kmalloc(desc->elem_size,
                                                       GFP_KERNEL);
                                        err = -ENOMEM;
                                        if (!elem)
                                                goto out;
                                }
                                if (encode) {
                                        if (!copied) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                        }
                                        memcpy(c, elem + copied, l);
                                        copied += l;
                                        if (copied == desc->elem_size)
                                                copied = 0;
                                } else {
                                        memcpy(elem + copied, c, l);
                                        copied += l;
                                        if (copied == desc->elem_size) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                                copied = 0;
                                        }
                                }
                        }
                        if (avail_here) {
                                kunmap(*ppages);
                                ppages++;
                                c = kmap(*ppages);
                        }

                        avail_page = min(avail_here,
                                 (unsigned int) PAGE_CACHE_SIZE);
                }
                base = buf->page_len;  /* align to start of tail */
        }

        /* process tail */
        base -= buf->page_len;
        if (todo) {
                c = buf->tail->iov_base + base;
                if (copied) {
                        unsigned int l = desc->elem_size - copied;

                        if (encode)
                                memcpy(c, elem + copied, l);
                        else {
                                memcpy(elem + copied, c, l);
                                err = desc->xcode(desc, elem);
                                if (err)
                                        goto out;
                        }
                        todo -= l;
                        c += l;
                }
                while (todo) {
                        err = desc->xcode(desc, c);
                        if (err)
                                goto out;
                        c += desc->elem_size;
                        todo -= desc->elem_size;
                }
        }
        err = 0;

out:
        kfree(elem);
        if (ppages)
                kunmap(*ppages);
        return err;
}

int
xdr_decode_array2(struct xdr_buf *buf, unsigned int base,
                  struct xdr_array2_desc *desc)
{
        if (base >= buf->len)
                return -EINVAL;

        return xdr_xcode_array2(buf, base, desc, 0);
}
EXPORT_SYMBOL_GPL(xdr_decode_array2);

int
xdr_encode_array2(struct xdr_buf *buf, unsigned int base,
                  struct xdr_array2_desc *desc)
{
        if ((unsigned long) base + 4 + desc->array_len * desc->elem_size >
            buf->head->iov_len + buf->page_len + buf->tail->iov_len)
                return -EINVAL;

        return xdr_xcode_array2(buf, base, desc, 1);
}
EXPORT_SYMBOL_GPL(xdr_encode_array2);

int
xdr_process_buf(struct xdr_buf *buf, unsigned int offset, unsigned int len,
                int (*actor)(struct scatterlist *, void *), void *data)
{
        int i, ret = 0;
        unsigned int page_len, thislen, page_offset;
        struct scatterlist      sg[1];

        sg_init_table(sg, 1);

        if (offset >= buf->head[0].iov_len) {
                offset -= buf->head[0].iov_len;
        } else {
                thislen = buf->head[0].iov_len - offset;
                if (thislen > len)
                        thislen = len;
                sg_set_buf(sg, buf->head[0].iov_base + offset, thislen);
                ret = actor(sg, data);
                if (ret)
                        goto out;
                offset = 0;
                len -= thislen;
        }
        if (len == 0)
                goto out;

        if (offset >= buf->page_len) {
                offset -= buf->page_len;
        } else {
                page_len = buf->page_len - offset;
                if (page_len > len)
                        page_len = len;
                len -= page_len;
                page_offset = (offset + buf->page_base) & (PAGE_CACHE_SIZE - 1);
                i = (offset + buf->page_base) >> PAGE_CACHE_SHIFT;
                thislen = PAGE_CACHE_SIZE - page_offset;
                do {
                        if (thislen > page_len)
                                thislen = page_len;
                        sg_set_page(sg, buf->pages[i], thislen, page_offset);
                        ret = actor(sg, data);
                        if (ret)
                                goto out;
                        page_len -= thislen;
                        i++;
                        page_offset = 0;
                        thislen = PAGE_CACHE_SIZE;
                } while (page_len != 0);
                offset = 0;
        }
        if (len == 0)
                goto out;
        if (offset < buf->tail[0].iov_len) {
                thislen = buf->tail[0].iov_len - offset;
                if (thislen > len)
                        thislen = len;
                sg_set_buf(sg, buf->tail[0].iov_base + offset, thislen);
                ret = actor(sg, data);
                len -= thislen;
        }
        if (len != 0)
                ret = -EINVAL;
out:
        return ret;
}
EXPORT_SYMBOL_GPL(xdr_process_buf);