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>
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@ -215,6 +215,7 @@ typedef int (*kxdrdproc_t)(void *rqstp, struct xdr_stream *xdr, void *obj);
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extern void xdr_init_encode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32 *p);
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extern __be32 *xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes);
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extern void xdr_truncate_encode(struct xdr_stream *xdr, size_t len);
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extern void xdr_write_pages(struct xdr_stream *xdr, struct page **pages,
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unsigned int base, unsigned int len);
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extern unsigned int xdr_stream_pos(const struct xdr_stream *xdr);
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@ -508,6 +508,72 @@ __be32 * xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes)
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}
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EXPORT_SYMBOL_GPL(xdr_reserve_space);
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/**
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* xdr_truncate_encode - truncate an encode buffer
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* @xdr: pointer to xdr_stream
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* @len: new length of buffer
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*
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* Truncates the xdr stream, so that xdr->buf->len == len,
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* and xdr->p points at offset len from the start of the buffer, and
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* head, tail, and page lengths are adjusted to correspond.
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*
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* If this means moving xdr->p to a different buffer, we assume that
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* that the end pointer should be set to the end of the current page,
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* except in the case of the head buffer when we assume the head
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* buffer's current length represents the end of the available buffer.
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*
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* This is *not* safe to use on a buffer that already has inlined page
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* cache pages (as in a zero-copy server read reply), except for the
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* simple case of truncating from one position in the tail to another.
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*
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*/
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void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
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{
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struct xdr_buf *buf = xdr->buf;
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struct kvec *head = buf->head;
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struct kvec *tail = buf->tail;
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int fraglen;
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int new, old;
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if (len > buf->len) {
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WARN_ON_ONCE(1);
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return;
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}
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fraglen = min_t(int, buf->len - len, tail->iov_len);
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tail->iov_len -= fraglen;
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buf->len -= fraglen;
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if (tail->iov_len && buf->len == len) {
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xdr->p = tail->iov_base + tail->iov_len;
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/* xdr->end, xdr->iov should be set already */
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return;
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}
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WARN_ON_ONCE(fraglen);
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fraglen = min_t(int, buf->len - len, buf->page_len);
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buf->page_len -= fraglen;
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buf->len -= fraglen;
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new = buf->page_base + buf->page_len;
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old = new + fraglen;
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xdr->page_ptr -= (old >> PAGE_SHIFT) - (new >> PAGE_SHIFT);
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if (buf->page_len && buf->len == len) {
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xdr->p = page_address(*xdr->page_ptr);
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xdr->end = (void *)xdr->p + PAGE_SIZE;
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xdr->p = (void *)xdr->p + (new % PAGE_SIZE);
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/* xdr->iov should already be NULL */
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return;
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}
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if (fraglen)
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xdr->end = head->iov_base + head->iov_len;
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/* (otherwise assume xdr->end is already set) */
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head->iov_len = len;
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buf->len = len;
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xdr->p = head->iov_base + head->iov_len;
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xdr->iov = buf->head;
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}
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EXPORT_SYMBOL(xdr_truncate_encode);
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/**
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* xdr_write_pages - Insert a list of pages into an XDR buffer for sending
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* @xdr: pointer to xdr_stream
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