SUNRPC/NFSD: Implement xdr_reserve_space_vec()

Reserving space for a large READ payload requires special handling when
reserving space in the xdr buffer pages. One problem we can have is use
of the scratch buffer, which is used to get a pointer to a contiguous
region of data up to PAGE_SIZE. When using the scratch buffer, calls to
xdr_commit_encode() shift the data to it's proper alignment in the xdr
buffer. If we've reserved several pages in a vector, then this could
potentially invalidate earlier pointers and result in incorrect READ
data being sent to the client.

I get around this by looking at the amount of space left in the current
page, and never reserve more than that for each entry in the read
vector. This lets us place data directly where it needs to go in the
buffer pages.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 3 insertions, 25 deletions

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 3d263fd20df0..36a54827085b 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3814,36 +3814,14 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp,
 {
 	struct xdr_stream *xdr = &resp->xdr;
 	u32 eof;
-	int v;
 	int starting_len = xdr->buf->len - 8;
-	long len;
-	int thislen;
 	__be32 nfserr;
 	__be32 tmp;
-	__be32 *p;
 	int pad;
 
-	/*
-	 * svcrdma requires every READ payload to start somewhere
-	 * in xdr->pages.
-	 */
-	if (xdr->iov == xdr->buf->head) {
-		xdr->iov = NULL;
-		xdr->end = xdr->p;
-	}
-
-	len = maxcount;
-	v = 0;
-	while (len) {
-		thislen = min_t(long, len, PAGE_SIZE);
-		p = xdr_reserve_space(xdr, thislen);
-		WARN_ON_ONCE(!p);
-		resp->rqstp->rq_vec[v].iov_base = p;
-		resp->rqstp->rq_vec[v].iov_len = thislen;
-		v++;
-		len -= thislen;
-	}
-	read->rd_vlen = v;
+	read->rd_vlen = xdr_reserve_space_vec(xdr, resp->rqstp->rq_vec, maxcount);
+	if (read->rd_vlen < 0)
+		return nfserr_resource;
 
 	nfserr = nfsd_readv(resp->rqstp, read->rd_fhp, file, read->rd_offset,
 			    resp->rqstp->rq_vec, read->rd_vlen, &maxcount,