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NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

PATCH Superseded [email protected] 3 participants 3 messages May 6, 2025 – May 7, 2025

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PATCH v2 1/1 NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

From: Chuck Lever <[email protected]>

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.

We assume this attribute reports a block size as a count of bytes, as RFC 7862 does not specify a unit.

Reported-by Roland Mainz <[email protected]>
Suggested-by Christoph Hellwig <[email protected]>

X-Cc: [email protected] # v6.7+

Signed-off-by Chuck Lever <[email protected]>
---
 fs/nfsd/nfs4xdr.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
fs/nfsd/nfs4xdr.c +9 -1
index e67420729ecd..59d186ea11dc 100644
@@ -3391,6 +3391,14 @@ 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)
+{
+	struct inode *inode = d_inode(args->dentry);
+
+	return nfsd4_encode_uint32_t(xdr, inode->i_sb->s_blocksize);
+}
+
 #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 +3553,7 @@ 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,
Signature · 1 line
2.49.0
#1 lore raw
Quoted 43 lines · On Tue, May 6, 2025 at 5:01 PM <[email protected]> wrote:

From: Chuck Lever <[email protected]>

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.

We assume this attribute reports a block size as a count of bytes, as RFC 7862 does not specify a unit.

Reported-by Roland Mainz <[email protected]>
Suggested-by Christoph Hellwig <[email protected]>

X-Cc: [email protected] # v6.7+

Signed-off-by Chuck Lever <[email protected]>
---
 fs/nfsd/nfs4xdr.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
fs/nfsd/nfs4xdr.c +8 -0
index e67420729ecd..59d186ea11dc 100644
@@ -3391,6 +3391,14 @@ 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)
+{
+       struct inode *inode = d_inode(args->dentry);
+
+       return nfsd4_encode_uint32_t(xdr, inode->i_sb->s_blocksize);
+}
+
 #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
 static __be32 nfsd4_encode_fattr4_sec_label(struct xdr_stream *xdr,
                                            const struct nfsd4_fattr_args *args)

fs/nfsd/nfs4xdr.c static const nfsd4_enc_attr nfsd4_enc_fattr4_encode_ops[] = { · line 3558

Quoted 7 lines
fs/nfsd/nfs4xdr.c +1 -1
@@ -3545,7 +3553,7 @@ 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,

Looks good to me - Reviewed-by: Roland Mainz <[email protected]>

----

Bye,
Roland

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#2 lore raw
In reply to [email protected]

fs/nfsd/nfs4xdr.c static __be32 nfsd4_encode_fattr4_suppattr_exclcreat(struct xdr_stream *xdr, · line 3395

Quoted 2 lines · On Tue, May 06, 2025 at 11:01:05AM -0400, [email protected] wrote:
fs/nfsd/nfs4xdr.c +2 -0
+static __be32 nfsd4_encode_fattr4_clone_blksize(struct xdr_stream *xdr,
+						const struct nfsd4_fattr_args *args)

Overly long line here. And easily avoided by using the much more maintainable two-tab indents for prototype continuations.

fs/nfsd/nfs4xdr.c static __be32 nfsd4_encode_fattr4_suppattr_exclcreat(struct xdr_stream *xdr, · line 3399

Quoted 4 lines
fs/nfsd/nfs4xdr.c +4 -0
+{
+	struct inode *inode = d_inode(args->dentry);
+
+	return nfsd4_encode_uint32_t(xdr, inode->i_sb->s_blocksize);

That's a bit of an assumption. The generic clone prep function uses the block size, but file systems aren't required to actually use generic_remap_file_range_prep.

Probably still the best we can do, but a comment explaining including a reference to generic_remap_checks / generic_remap_file_range_prep would be very useful here.