[PATCH v2] NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

[PATCH v2] NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

[cel]

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.

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 <roland.mainz@nrubsig.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
X-Cc: stable@vger.kernel.org # v6.7+
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4xdr.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index e67420729ecd..59d186ea11dc 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -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,
 
-- 
2.49.0

Re: [PATCH v2] NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

[Roland Mainz]

On Tue, May 6, 2025 at 5:01 PM <cel@kernel.org> wrote:
>
> 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.
>
> 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 <roland.mainz@nrubsig.org>
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> X-Cc: stable@vger.kernel.org # v6.7+
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/nfs4xdr.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index e67420729ecd..59d186ea11dc 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -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,

Looks good to me -  Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>

----

Bye,
Roland
-- 
  __ .  . __
 (o.\ \/ /.o) roland.mainz@nrubsig.org
  \__\/\/__/  MPEG specialist, C&&JAVA&&Sun&&Unix programmer
  /O /==\ O\  TEL +49 641 3992797
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Re: [PATCH v2] NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

[Christoph Hellwig]

On Tue, May 06, 2025 at 11:01:05AM -0400, cel@kernel.org wrote:
> +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.

> +{
> +	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.