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rpc: xdr_truncate_encode 

This will be used in the server side in a few cases:
	- when certain operations (read, readdir, readlink) fail after
	  encoding a partial response.
	- when we run out of space after encoding a partial response.
	- in readlink, where we initially reserve PAGE_SIZE bytes for
	  data, then truncate to the actual size.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
J. Bruce Fields 2014-02-25 17:44:21 -05:00
parent 6ac90391c6
commit 3e19ce762b
2 changed files with 67 additions and 0 deletions
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1
include/linux/sunrpc/xdr.h
View File

@ -215,6 +215,7 @@ typedef int (*kxdrdproc_t)(void *rqstp, struct xdr_stream *xdr, void *obj);
extern void xdr_init_encode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32 *p);
extern __be32 *xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes);
extern void xdr_truncate_encode(struct xdr_stream *xdr, size_t len);
extern void xdr_write_pages(struct xdr_stream *xdr, struct page **pages,
unsigned int base, unsigned int len);
extern unsigned int xdr_stream_pos(const struct xdr_stream *xdr);

66
net/sunrpc/xdr.c
View File

@ -508,6 +508,72 @@ __be32 * xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes)
}
EXPORT_SYMBOL_GPL(xdr_reserve_space);
/**
* xdr_truncate_encode - truncate an encode buffer
* @xdr: pointer to xdr_stream
* @len: new length of buffer
*
* Truncates the xdr stream, so that xdr->buf->len == len,
* and xdr->p points at offset len from the start of the buffer, and
* head, tail, and page lengths are adjusted to correspond.
*
* If this means moving xdr->p to a different buffer, we assume that
* that the end pointer should be set to the end of the current page,
* except in the case of the head buffer when we assume the head
* buffer's current length represents the end of the available buffer.
*
* This is *not* safe to use on a buffer that already has inlined page
* cache pages (as in a zero-copy server read reply), except for the
* simple case of truncating from one position in the tail to another.
*
*/
void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
{
struct xdr_buf *buf = xdr->buf;
struct kvec *head = buf->head;
struct kvec *tail = buf->tail;
int fraglen;
int new, old;
if (len > buf->len) {
WARN_ON_ONCE(1);
return;
}
fraglen = min_t(int, buf->len - len, tail->iov_len);
tail->iov_len -= fraglen;
buf->len -= fraglen;
if (tail->iov_len && buf->len == len) {
xdr->p = tail->iov_base + tail->iov_len;
/* xdr->end, xdr->iov should be set already */
return;
}
WARN_ON_ONCE(fraglen);
fraglen = min_t(int, buf->len - len, buf->page_len);
buf->page_len -= fraglen;
buf->len -= fraglen;
new = buf->page_base + buf->page_len;
old = new + fraglen;
xdr->page_ptr -= (old >> PAGE_SHIFT) - (new >> PAGE_SHIFT);
if (buf->page_len && buf->len == len) {
xdr->p = page_address(*xdr->page_ptr);
xdr->end = (void *)xdr->p + PAGE_SIZE;
xdr->p = (void *)xdr->p + (new % PAGE_SIZE);
/* xdr->iov should already be NULL */
return;
}
if (fraglen)
xdr->end = head->iov_base + head->iov_len;
/* (otherwise assume xdr->end is already set) */
head->iov_len = len;
buf->len = len;
xdr->p = head->iov_base + head->iov_len;
xdr->iov = buf->head;
}
EXPORT_SYMBOL(xdr_truncate_encode);
/**
* xdr_write_pages - Insert a list of pages into an XDR buffer for sending
* @xdr: pointer to xdr_stream