1 files changed, 917 insertions, 0 deletions

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
new file mode 100644
index 000000000000..4484931018eb
--- /dev/null
+++ b/net/sunrpc/xdr.c
@@ -0,0 +1,917 @@
+/*
+ * linux/net/sunrpc/xdr.c
+ *
+ * Generic XDR support.
+ *
+ * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
+ */
+
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/string.h>
+#include <linux/kernel.h>
+#include <linux/pagemap.h>
+#include <linux/errno.h>
+#include <linux/in.h>
+#include <linux/net.h>
+#include <net/sock.h>
+#include <linux/sunrpc/xdr.h>
+#include <linux/sunrpc/msg_prot.h>
+
+/*
+ * XDR functions for basic NFS types
+ */
+u32 *
+xdr_encode_netobj(u32 *p, const struct xdr_netobj *obj)
+{
+        unsigned int    quadlen = XDR_QUADLEN(obj->len);
+
+        p[quadlen] = 0;         /* zero trailing bytes */
+        *p++ = htonl(obj->len);
+        memcpy(p, obj->data, obj->len);
+        return p + XDR_QUADLEN(obj->len);
+}
+
+u32 *
+xdr_decode_netobj(u32 *p, struct xdr_netobj *obj)
+{
+        unsigned int    len;
+
+        if ((len = ntohl(*p++)) > XDR_MAX_NETOBJ)
+                return NULL;
+        obj->len  = len;
+        obj->data = (u8 *) p;
+        return p + XDR_QUADLEN(len);
+}
+
+/**
+ * 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
+ *
+ */
+u32 *xdr_encode_opaque_fixed(u32 *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(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
+ */
+u32 *xdr_encode_opaque(u32 *p, const void *ptr, unsigned int nbytes)
+{
+        *p++ = htonl(nbytes);
+        return xdr_encode_opaque_fixed(p, ptr, nbytes);
+}
+EXPORT_SYMBOL(xdr_encode_opaque);
+
+u32 *
+xdr_encode_string(u32 *p, const char *string)
+{
+        return xdr_encode_array(p, string, strlen(string));
+}
+
+u32 *
+xdr_decode_string(u32 *p, char **sp, int *lenp, int maxlen)
+{
+        unsigned int    len;
+        char            *string;
+
+        if ((len = ntohl(*p++)) > maxlen)
+                return NULL;
+        if (lenp)
+                *lenp = len;
+        if ((len % 4) != 0) {
+                string = (char *) p;
+        } else {
+                string = (char *) (p - 1);
+                memmove(string, p, len);
+        }
+        string[len] = '\0';
+        *sp = string;
+        return p + XDR_QUADLEN(len);
+}
+
+u32 *
+xdr_decode_string_inplace(u32 *p, char **sp, int *lenp, int maxlen)
+{
+        unsigned int    len;
+
+        if ((len = ntohl(*p++)) > maxlen)
+                return NULL;
+        *lenp = len;
+        *sp = (char *) p;
+        return p + XDR_QUADLEN(len);
+}
+
+void
+xdr_encode_pages(struct xdr_buf *xdr, struct page **pages, unsigned int base,
+                 unsigned int len)
+{
+        struct kvec *tail = xdr->tail;
+        u32 *p;
+
+        xdr->pages = pages;
+        xdr->page_base = base;
+        xdr->page_len = len;
+
+        p = (u32 *)xdr->head[0].iov_base + XDR_QUADLEN(xdr->head[0].iov_len);
+        tail->iov_base = p;
+        tail->iov_len = 0;
+
+        if (len & 3) {
+                unsigned int pad = 4 - (len & 3);
+
+                *p = 0;
+                tail->iov_base = (char *)p + (len & 3);
+                tail->iov_len  = pad;
+                len += pad;
+        }
+        xdr->buflen += len;
+        xdr->len += len;
+}
+
+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;
+}
+
+void
+xdr_partial_copy_from_skb(struct xdr_buf *xdr, unsigned int base,
+                          skb_reader_t *desc,
+                          skb_read_actor_t copy_actor)
+{
+        struct page     **ppage = xdr->pages;
+        unsigned int    len, pglen = xdr->page_len;
+        int             ret;
+
+        len = xdr->head[0].iov_len;
+        if (base < len) {
+                len -= base;
+                ret = copy_actor(desc, (char *)xdr->head[0].iov_base + base, len);
+                if (ret != len || !desc->count)
+                        return;
+                base = 0;
+        } else
+                base -= len;
+
+        if (pglen == 0)
+                goto copy_tail;
+        if (base >= pglen) {
+                base -= pglen;
+                goto copy_tail;
+        }
+        if (base || xdr->page_base) {
+                pglen -= base;
+                base  += xdr->page_base;
+                ppage += base >> PAGE_CACHE_SHIFT;
+                base &= ~PAGE_CACHE_MASK;
+        }
+        do {
+                char *kaddr;
+
+                len = PAGE_CACHE_SIZE;
+                kaddr = kmap_atomic(*ppage, KM_SKB_SUNRPC_DATA);
+                if (base) {
+                        len -= base;
+                        if (pglen < len)
+                                len = pglen;
+                        ret = copy_actor(desc, kaddr + base, len);
+                        base = 0;
+                } else {
+                        if (pglen < len)
+                                len = pglen;
+                        ret = copy_actor(desc, kaddr, len);
+                }
+                flush_dcache_page(*ppage);
+                kunmap_atomic(kaddr, KM_SKB_SUNRPC_DATA);
+                if (ret != len || !desc->count)
+                        return;
+                ppage++;
+        } while ((pglen -= len) != 0);
+copy_tail:
+        len = xdr->tail[0].iov_len;
+        if (base < len)
+                copy_actor(desc, (char *)xdr->tail[0].iov_base + base, len - base);
+}
+
+
+int
+xdr_sendpages(struct socket *sock, struct sockaddr *addr, int addrlen,
+                struct xdr_buf *xdr, unsigned int base, int msgflags)
+{
+        struct page **ppage = xdr->pages;
+        unsigned int len, pglen = xdr->page_len;
+        int err, ret = 0;
+        ssize_t (*sendpage)(struct socket *, struct page *, int, size_t, int);
+
+        len = xdr->head[0].iov_len;
+        if (base < len || (addr != NULL && base == 0)) {
+                struct kvec iov = {
+                        .iov_base = xdr->head[0].iov_base + base,
+                        .iov_len  = len - base,
+                };
+                struct msghdr msg = {
+                        .msg_name    = addr,
+                        .msg_namelen = addrlen,
+                        .msg_flags   = msgflags,
+                };
+                if (xdr->len > len)
+                        msg.msg_flags |= MSG_MORE;
+
+                if (iov.iov_len != 0)
+                        err = kernel_sendmsg(sock, &msg, &iov, 1, iov.iov_len);
+                else
+                        err = kernel_sendmsg(sock, &msg, NULL, 0, 0);
+                if (ret == 0)
+                        ret = err;
+                else if (err > 0)
+                        ret += err;
+                if (err != iov.iov_len)
+                        goto out;
+                base = 0;
+        } else
+                base -= len;
+
+        if (pglen == 0)
+                goto copy_tail;
+        if (base >= pglen) {
+                base -= pglen;
+                goto copy_tail;
+        }
+        if (base || xdr->page_base) {
+                pglen -= base;
+                base  += xdr->page_base;
+                ppage += base >> PAGE_CACHE_SHIFT;
+                base &= ~PAGE_CACHE_MASK;
+        }
+
+        sendpage = sock->ops->sendpage ? : sock_no_sendpage;
+        do {
+                int flags = msgflags;
+
+                len = PAGE_CACHE_SIZE;
+                if (base)
+                        len -= base;
+                if (pglen < len)
+                        len = pglen;
+
+                if (pglen != len || xdr->tail[0].iov_len != 0)
+                        flags |= MSG_MORE;
+
+                /* Hmm... We might be dealing with highmem pages */
+                if (PageHighMem(*ppage))
+                        sendpage = sock_no_sendpage;
+                err = sendpage(sock, *ppage, base, len, flags);
+                if (ret == 0)
+                        ret = err;
+                else if (err > 0)
+                        ret += err;
+                if (err != len)
+                        goto out;
+                base = 0;
+                ppage++;
+        } while ((pglen -= len) != 0);
+copy_tail:
+        len = xdr->tail[0].iov_len;
+        if (base < len) {
+                struct kvec iov = {
+                        .iov_base = xdr->tail[0].iov_base + base,
+                        .iov_len  = len - base,
+                };
+                struct msghdr msg = {
+                        .msg_flags   = msgflags,
+                };
+                err = kernel_sendmsg(sock, &msg, &iov, 1, iov.iov_len);
+                if (ret == 0)
+                        ret = err;
+                else if (err > 0)
+                        ret += err;
+        }
+out:
+        return ret;
+}
+
+
+/*
+ * 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) {
+                        flush_dcache_page(*pgto);
+                        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, KM_USER0);
+                vfrom = kmap_atomic(*pgfrom, KM_USER1);
+                memmove(vto + pgto_base, vfrom + pgfrom_base, copy);
+                kunmap_atomic(vfrom, KM_USER1);
+                kunmap_atomic(vto, KM_USER0);
+
+        } while ((len -= copy) != 0);
+        flush_dcache_page(*pgto);
+}
+
+/*
+ * _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;
+
+        do {
+                copy = PAGE_CACHE_SIZE - pgbase;
+                if (copy > len)
+                        copy = len;
+
+                vto = kmap_atomic(*pgto, KM_USER0);
+                memcpy(vto + pgbase, p, copy);
+                kunmap_atomic(vto, KM_USER0);
+
+                pgbase += copy;
+                if (pgbase == PAGE_CACHE_SIZE) {
+                        flush_dcache_page(*pgto);
+                        pgbase = 0;
+                        pgto++;
+                }
+                p += copy;
+
+        } while ((len -= copy) != 0);
+        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.
+ */
+static 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, KM_USER0);
+                memcpy(p, vfrom + pgbase, copy);
+                kunmap_atomic(vfrom, KM_USER0);
+
+                pgbase += copy;
+                if (pgbase == PAGE_CACHE_SIZE) {
+                        pgbase = 0;
+                        pgfrom++;
+                }
+                p += copy;
+
+        } while ((len -= copy) != 0);
+}
+
+/*
+ * 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;
+        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;
+}
+
+/*
+ * 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;
+        char *p;
+        unsigned int pglen = buf->page_len;
+
+        tail = buf->tail;
+        BUG_ON (len > pglen);
+
+        /* Shift the tail first */
+        if (tail->iov_len != 0) {
+                p = (char *)tail->iov_base + len;
+                if (tail->iov_len > len) {
+                        copy = tail->iov_len - len;
+                        memmove(p, tail->iov_base, copy);
+                } else
+                        buf->buflen -= len;
+                /* Copy from the inlined pages into the tail */
+                copy = len;
+                if (copy > tail->iov_len)
+                        copy = tail->iov_len;
+                _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);
+}
+
+/**
+ * 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, uint32_t *p)
+{
+        struct kvec *iov = buf->head;
+
+        xdr->buf = buf;
+        xdr->iov = iov;
+        xdr->end = (uint32_t *)((char *)iov->iov_base + iov->iov_len);
+        buf->len = iov->iov_len = (char *)p - (char *)iov->iov_base;
+        xdr->p = p;
+}
+EXPORT_SYMBOL(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.
+ */
+uint32_t * xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes)
+{
+        uint32_t *p = xdr->p;
+        uint32_t *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(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(xdr_write_pages);
+
+/**
+ * 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, uint32_t *p)
+{
+        struct kvec *iov = buf->head;
+        unsigned int len = iov->iov_len;
+
+        if (len > buf->len)
+                len = buf->len;
+        xdr->buf = buf;
+        xdr->iov = iov;
+        xdr->p = p;
+        xdr->end = (uint32_t *)((char *)iov->iov_base + len);
+}
+EXPORT_SYMBOL(xdr_init_decode);
+
+/**
+ * xdr_inline_decode - Retrieve non-page 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.
+ */
+uint32_t * xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
+{
+        uint32_t *p = xdr->p;
+        uint32_t *q = p + XDR_QUADLEN(nbytes);
+
+        if (unlikely(q > xdr->end || q < p))
+                return NULL;
+        xdr->p = q;
+        return p;
+}
+EXPORT_SYMBOL(xdr_inline_decode);
+
+/**
+ * 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[]. The current pointer is then
+ * repositioned at the beginning of the XDR tail.
+ */
+void xdr_read_pages(struct xdr_stream *xdr, unsigned int len)
+{
+        struct xdr_buf *buf = xdr->buf;
+        struct kvec *iov;
+        ssize_t shift;
+        unsigned int end;
+        int padding;
+
+        /* Realign pages to current pointer position */
+        iov  = buf->head;
+        shift = iov->iov_len + (char *)iov->iov_base - (char *)xdr->p;
+        if (shift > 0)
+                xdr_shrink_bufhead(buf, shift);
+
+        /* Truncate page data and move it into the tail */
+        if (buf->page_len > len)
+                xdr_shrink_pagelen(buf, buf->page_len - len);
+        padding = (XDR_QUADLEN(len) << 2) - len;
+        xdr->iov = iov = buf->tail;
+        /* Compute remaining message length.  */
+        end = iov->iov_len;
+        shift = buf->buflen - buf->len;
+        if (shift < end)
+                end -= shift;
+        else if (shift > 0)
+                end = 0;
+        /*
+         * Position current pointer at beginning of tail, and
+         * set remaining message length.
+         */
+        xdr->p = (uint32_t *)((char *)iov->iov_base + padding);
+        xdr->end = (uint32_t *)((char *)iov->iov_base + end);
+}
+EXPORT_SYMBOL(xdr_read_pages);
+
+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;
+}
+
+/* Sets subiov to the intersection of iov with the buffer of length len
+ * starting base bytes after iov.  Indicates empty intersection by setting
+ * length of subiov to zero.  Decrements len by length of subiov, sets base
+ * to zero (or decrements it by length of iov if subiov is empty). */
+static void
+iov_subsegment(struct kvec *iov, struct kvec *subiov, int *base, int *len)
+{
+        if (*base > iov->iov_len) {
+                subiov->iov_base = NULL;
+                subiov->iov_len = 0;
+                *base -= iov->iov_len;
+        } else {
+                subiov->iov_base = iov->iov_base + *base;
+                subiov->iov_len = min(*len, (int)iov->iov_len - *base);
+                *base = 0;
+        }
+        *len -= subiov->iov_len; 
+}
+
+/* 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,
+                        int base, int len)
+{
+        int i;
+
+        subbuf->buflen = subbuf->len = len;
+        iov_subsegment(buf->head, subbuf->head, &base, &len);
+
+        if (base < buf->page_len) {
+                i = (base + buf->page_base) >> PAGE_CACHE_SHIFT;
+                subbuf->pages = &buf->pages[i];
+                subbuf->page_base = (base + buf->page_base) & ~PAGE_CACHE_MASK;
+                subbuf->page_len = min((int)buf->page_len - base, len);
+                len -= subbuf->page_len;
+                base = 0;
+        } else {
+                base -= buf->page_len;
+                subbuf->page_len = 0;
+        }
+
+        iov_subsegment(buf->tail, subbuf->tail, &base, &len);
+        if (base || len)
+                return -1;
+        return 0;
+}
+
+/* obj is assumed to point to allocated memory of size at least len: */
+int
+read_bytes_from_xdr_buf(struct xdr_buf *buf, int base, void *obj, int len)
+{
+        struct xdr_buf subbuf;
+        int this_len;
+        int status;
+
+        status = xdr_buf_subsegment(buf, &subbuf, base, len);
+        if (status)
+                goto out;
+        this_len = min(len, (int)subbuf.head[0].iov_len);
+        memcpy(obj, subbuf.head[0].iov_base, this_len);
+        len -= this_len;
+        obj += this_len;
+        this_len = min(len, (int)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(len, (int)subbuf.tail[0].iov_len);
+        memcpy(obj, subbuf.tail[0].iov_base, this_len);
+out:
+        return status;
+}
+
+static int
+read_u32_from_xdr_buf(struct xdr_buf *buf, int base, u32 *obj)
+{
+        u32     raw;
+        int     status;
+
+        status = read_bytes_from_xdr_buf(buf, base, &raw, sizeof(*obj));
+        if (status)
+                return status;
+        *obj = ntohl(raw);
+        return 0;
+}
+
+/* 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, int offset)
+{
+        u32     tail_offset = buf->head[0].iov_len + buf->page_len;
+        u32     obj_end_offset;
+
+        if (read_u32_from_xdr_buf(buf, offset, &obj->len))
+                goto out;
+        obj_end_offset = offset + 4 + obj->len;
+
+        if (obj_end_offset <= buf->head[0].iov_len) {
+                /* The obj is contained entirely in the head: */
+                obj->data = buf->head[0].iov_base + offset + 4;
+        } else if (offset + 4 >= tail_offset) {
+                if (obj_end_offset - tail_offset
+                                > buf->tail[0].iov_len)
+                        goto out;
+                /* The obj is contained entirely in the tail: */
+                obj->data = buf->tail[0].iov_base
+                        + offset - tail_offset + 4;
+        } else {
+                /* 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->tail[0].iov_len)
+                        goto out;
+                obj->data = buf->tail[0].iov_base + buf->tail[0].iov_len - 
+                                obj->len;
+                if (read_bytes_from_xdr_buf(buf, offset + 4,
+                                        obj->data, obj->len))
+                        goto out;
+
+        }
+        return 0;
+out:
+        return -1;
+}