From d7de37d6d7ccfac9321d8cc4f36fc85dfadad54a Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Wed, 8 Oct 2025 09:52:29 -0400 Subject: [PATCH] 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 Reviewed-by: Jeff Layton Signed-off-by: Chuck Lever --- fs/nfsd/nfs4xdr.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 494a703e0570..30ce5851fe4c 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -4480,18 +4480,30 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp, __be32 zero = xdr_zero; __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, read->rd_offset, &maxcount, base, &read->rd_eof); read->rd_length = maxcount; if (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)) return nfserr_io; - xdr_truncate_encode(xdr, starting_len + xdr_align_size(maxcount)); write_bytes_to_xdr_buf(xdr->buf, starting_len + maxcount, &zero, xdr_pad_size(maxcount));