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Commit 3e19ce76 authored by J. Bruce Fields's avatar J. Bruce Fields
Browse files

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: default avatarJ. Bruce Fields <bfields@redhat.com>
parent 6ac90391

include/linux/sunrpc/xdr.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

net/sunrpc/xdr.c

+66 −0
Original line number Diff line number Diff line
@@ -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