From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
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@xxxxxxxxxx>
---
include/linux/sunrpc/xdr.h | 1 +
net/sunrpc/xdr.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 68 insertions(+)
diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index 15f9204..e7bb2e3 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -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);
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index dd97ba3..8ae8ee7 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -509,6 +509,73 @@ __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;
+ xdr->page_ptr -= 1;
+}
+EXPORT_SYMBOL(xdr_truncate_encode);
+
+/**
* xdr_write_pages - Insert a list of pages into an XDR buffer for sending
* @xdr: pointer to xdr_stream
* @pages: list of pages
--
1.9.0
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