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NFSD: Relocate the xdr_reserve_space_vec() call site 

In order to detect when a direct READ is possible, we need the send
buffer's .page_len to be zero when there is nothing in the buffer's
.pages array yet.

However, when xdr_reserve_space_vec() extends the size of the
xdr_stream to accommodate a READ payload, it adds to the send
buffer's .page_len.

It should be safe to reserve the stream space /after/ the VFS read
operation completes. This is, for example, how an NFSv3 READ works:
the VFS read goes into the rq_bvec, and is then added to the send
xdr_stream later by svcxdr_encode_opaque_pages().

Now that xdr_reserve_space_vec() uses the number of bytes actually
read, the xdr_truncate_encode() call is no longer necessary.

Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
pull/1354/merge
Chuck Lever 2025-10-08 09:52:29 -04:00
parent 803bc849f0
commit d7de37d6d7
1 changed files with 16 additions and 4 deletions
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20
fs/nfsd/nfs4xdr.c
View File

@ -4480,18 +4480,30 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp,
__be32 zero = xdr_zero; __be32 zero = xdr_zero;
__be32 nfserr; __be32 nfserr;
if (xdr_reserve_space_vec(xdr, maxcount) < 0)
return nfserr_resource;
nfserr = nfsd_iter_read(resp->rqstp, read->rd_fhp, read->rd_nf, nfserr = nfsd_iter_read(resp->rqstp, read->rd_fhp, read->rd_nf,
read->rd_offset, &maxcount, base, read->rd_offset, &maxcount, base,
&read->rd_eof); &read->rd_eof);
read->rd_length = maxcount; read->rd_length = maxcount;
if (nfserr) if (nfserr)
return nfserr; return nfserr;
/*
* svcxdr_encode_opaque_pages() is not used here because
* we don't want to encode subsequent results in this
* COMPOUND into the xdr->buf's tail, but rather those
* results should follow the NFS READ payload in the
* buf's pages.
*/
if (xdr_reserve_space_vec(xdr, maxcount) < 0)
return nfserr_resource;
/*
* Mark the buffer location of the NFS READ payload so that
* direct placement-capable transports send only the
* payload bytes out-of-band.
*/
if (svc_encode_result_payload(resp->rqstp, starting_len, maxcount)) if (svc_encode_result_payload(resp->rqstp, starting_len, maxcount))
return nfserr_io; return nfserr_io;
xdr_truncate_encode(xdr, starting_len + xdr_align_size(maxcount));
write_bytes_to_xdr_buf(xdr->buf, starting_len + maxcount, &zero, write_bytes_to_xdr_buf(xdr->buf, starting_len + maxcount, &zero,
xdr_pad_size(maxcount)); xdr_pad_size(maxcount));