xdr.c

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/*
 * linux/net/sunrpc/xdr.c
 *
 * Generic XDR support.
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <[email protected]>
 */

#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);

__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);

__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);

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
 */

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);
        vfrom = kmap_atomic(*pgfrom);
        memmove(vto + pgto_base, vfrom + pgfrom_base, copy);
        flush_dcache_page(*pgto);
        kunmap_atomic(vfrom);
        kunmap_atomic(vto);

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

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);
}

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);

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;
    BUG_ON (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;
}

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);

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);

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);

__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);

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;
}

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);

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;
}

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;
}

__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;
}

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);

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);

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);