[PATCH] NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

[cel@kernel.org]

From: Chuck Lever <chuck.lever@oracle.com>

RFC 7862 states that if an NFS server implements a CLONE operation,
it MUST also implement FATTR4_CLONE_BLKSIZE. NFSD implements CLONE,
but does not implement FATTR4_CLONE_BLKSIZE.

Note that in Section 12.2, RFC 7862 claims that
FATTR4_CLONE_BLKSIZE is RECOMMENDED, not REQUIRED. Likely this is
because a minor version is not permitted to add a REQUIRED
attribute. Confusing.

NFSD can return 0 here, as at least one client implementation we
are aware of (the Linux NFS client) treats 0 as meaning "CLONE has
no alignment restrictions".

Meanwhile we need to consult the nfsv4 Working Group to clarify the
meaning and use of the value of this attribute.

Reported-by: Roland Mainz <roland.mainz@nrubsig.org>
X-Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4xdr.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index e67420729ecd..44e7fb34f433 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3391,6 +3391,13 @@ static __be32 nfsd4_encode_fattr4_suppattr_exclcreat(struct xdr_stream *xdr,
 	return nfsd4_encode_bitmap4(xdr, supp[0], supp[1], supp[2]);
 }
 
+static __be32 nfsd4_encode_fattr4_clone_blksize(struct xdr_stream *xdr,
+						const struct nfsd4_fattr_args *args)
+{
+	/* Linux filesystems have no clone alignment restrictions */
+	return nfsd4_encode_uint32_t(xdr, 0);
+}
+
 #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
 static __be32 nfsd4_encode_fattr4_sec_label(struct xdr_stream *xdr,
 					    const struct nfsd4_fattr_args *args)
@@ -3545,7 +3552,7 @@ static const nfsd4_enc_attr nfsd4_enc_fattr4_encode_ops[] = {
 	[FATTR4_MODE_SET_MASKED]	= nfsd4_encode_fattr4__noop,
 	[FATTR4_SUPPATTR_EXCLCREAT]	= nfsd4_encode_fattr4_suppattr_exclcreat,
 	[FATTR4_FS_CHARSET_CAP]		= nfsd4_encode_fattr4__noop,
-	[FATTR4_CLONE_BLKSIZE]		= nfsd4_encode_fattr4__noop,
+	[FATTR4_CLONE_BLKSIZE]		= nfsd4_encode_fattr4_clone_blksize,
 	[FATTR4_SPACE_FREED]		= nfsd4_encode_fattr4__noop,
 	[FATTR4_CHANGE_ATTR_TYPE]	= nfsd4_encode_fattr4__noop,
 
-- 
2.49.0