Re: [PATCH 06/10] NFSD: Enable return of an updated stable_how to NFS clients

On Thu, 2026-05-28 at 17:55 -0400, Jeff Layton wrote:
> From: Chuck Lever <[email protected]>
> 
> In a subsequent patch, nfsd_vfs_write() will promote an UNSTABLE
> WRITE to be a FILE_SYNC WRITE. This indicates that the client does
> not need a subsequent COMMIT operation, saving a round trip and
> allowing the client to dispense with cached dirty data as soon as
> it receives the server's WRITE response.
> 
> This patch refactors nfsd_vfs_write() to return a possibly modified
> stable_how value to its callers. No behavior change is expected.
> 
> Reviewed-by: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>
> Reviewed-by: Jeff Layton <[email protected]>
> Fixes: 3f3503adb332 ("NFSD: Use vfs_iocb_iter_write()")
> Signed-off-by: Chuck Lever <[email protected]>
> ---
>  fs/nfsd/nfs3proc.c |  2 +-
>  fs/nfsd/nfs4proc.c |  2 +-
>  fs/nfsd/nfsproc.c  |  3 ++-
>  fs/nfsd/vfs.c      | 11 ++++++-----
>  fs/nfsd/vfs.h      |  6 ++++--
>  fs/nfsd/xdr3.h     |  2 +-
>  6 files changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
> index aeda7a802bdf..dd5ac59e87d6 100644
> --- a/fs/nfsd/nfs3proc.c
> +++ b/fs/nfsd/nfs3proc.c
> @@ -236,7 +236,7 @@ nfsd3_proc_write(struct svc_rqst *rqstp)
>  	resp->committed = argp->stable;
>  	resp->status = nfsd_write(rqstp, &resp->fh, argp->offset,
>  				  &argp->payload, &cnt,
> -				  resp->committed, resp->verf);
> +				  &resp->committed, resp->verf);
>  	resp->count = cnt;
>  	resp->status = nfsd3_map_status(resp->status);
>  	return rpc_success;
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 5f2b9bfc3a84..ac03f9d89288 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -1355,7 +1355,7 @@ nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	write->wr_how_written = write->wr_stable_how;
>  	status = nfsd_vfs_write(rqstp, &cstate->current_fh, nf,
>  				write->wr_offset, &write->wr_payload,
> -				&cnt, write->wr_how_written,
> +				&cnt, &write->wr_how_written,
>  				(__be32 *)write->wr_verifier.data);
>  	nfsd_file_put(nf);
>  
> diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
> index 8873033d1e82..d0a7316f00a5 100644
> --- a/fs/nfsd/nfsproc.c
> +++ b/fs/nfsd/nfsproc.c
> @@ -251,6 +251,7 @@ nfsd_proc_write(struct svc_rqst *rqstp)
>  	struct nfsd_writeargs *argp = rqstp->rq_argp;
>  	struct nfsd_attrstat *resp = rqstp->rq_resp;
>  	unsigned long cnt = argp->len;
> +	u32 committed = NFS_DATA_SYNC;
>  
>  	dprintk("nfsd: WRITE    %s %u bytes at %d\n",
>  		SVCFH_fmt(&argp->fh),
> @@ -258,7 +259,7 @@ nfsd_proc_write(struct svc_rqst *rqstp)
>  
>  	fh_copy(&resp->fh, &argp->fh);
>  	resp->status = nfsd_write(rqstp, &resp->fh, argp->offset,
> -				  &argp->payload, &cnt, NFS_DATA_SYNC, NULL);
> +				  &argp->payload, &cnt, &committed, NULL);
>  	if (resp->status == nfs_ok)
>  		resp->status = fh_getattr(&resp->fh, &resp->stat);
>  	else if (resp->status == nfserr_jukebox)
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 1e89c7ff9493..7f07292d1569 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1414,7 +1414,7 @@ nfsd_direct_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
>   * @offset: Byte offset of start
>   * @payload: xdr_buf containing the write payload
>   * @cnt: IN: number of bytes to write, OUT: number of bytes actually written
> - * @stable: An NFS stable_how value
> + * @stable_how: IN: Client's requested stable_how, OUT: Actual stable_how
>   * @verf: NFS WRITE verifier
>   *
>   * Upon return, caller must invoke fh_put on @fhp.
> @@ -1426,11 +1426,12 @@ __be32
>  nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  	       struct nfsd_file *nf, loff_t offset,
>  	       const struct xdr_buf *payload, unsigned long *cnt,
> -	       int stable, __be32 *verf)
> +	       u32 *stable_how, __be32 *verf)
>  {
>  	struct nfsd_net		*nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
>  	struct file		*file = nf->nf_file;
>  	struct super_block	*sb = file_inode(file)->i_sb;
> +	u32			stable = *stable_how;
>  	struct kiocb		kiocb;
>  	struct svc_export	*exp;
>  	struct iov_iter		iter;
> @@ -1609,7 +1610,7 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
>   * @offset: Byte offset of start
>   * @payload: xdr_buf containing the write payload
>   * @cnt: IN: number of bytes to write, OUT: number of bytes actually written
> - * @stable: An NFS stable_how value
> + * @stable_how: IN: Client's requested stable_how, OUT: Actual stable_how
>   * @verf: NFS WRITE verifier
>   *
>   * Upon return, caller must invoke fh_put on @fhp.
> @@ -1619,7 +1620,7 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
>   */
>  __be32
>  nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t offset,
> -	   const struct xdr_buf *payload, unsigned long *cnt, int stable,
> +	   const struct xdr_buf *payload, unsigned long *cnt, u32 *stable_how,
>  	   __be32 *verf)
>  {
>  	struct nfsd_file *nf;
> @@ -1632,7 +1633,7 @@ nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t offset,
>  		goto out;
>  
>  	err = nfsd_vfs_write(rqstp, fhp, nf, offset, payload, cnt,
> -			     stable, verf);
> +			     stable_how, verf);
>  	nfsd_file_put(nf);
>  out:
>  	trace_nfsd_write_done(rqstp, fhp, offset, *cnt);
> diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> index e09ea04a51b9..36cd9f6edd8b 100644
> --- a/fs/nfsd/vfs.h
> +++ b/fs/nfsd/vfs.h
> @@ -132,11 +132,13 @@ __be32		nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  				u32 *eof);
>  __be32		nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  				loff_t offset, const struct xdr_buf *payload,
> -				unsigned long *cnt, int stable, __be32 *verf);
> +				unsigned long *cnt, u32 *stable_how,
> +				__be32 *verf);
>  __be32		nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  				struct nfsd_file *nf, loff_t offset,
>  				const struct xdr_buf *payload,
> -				unsigned long *cnt, int stable, __be32 *verf);
> +				unsigned long *cnt, u32 *stable_how,
> +				__be32 *verf);
>  __be32		nfsd_readlink(struct svc_rqst *, struct svc_fh *,
>  				char *, int *);
>  __be32		nfsd_symlink(struct svc_rqst *, struct svc_fh *,
> diff --git a/fs/nfsd/xdr3.h b/fs/nfsd/xdr3.h
> index a7c9714b0b0e..1ff7b11c397c 100644
> --- a/fs/nfsd/xdr3.h
> +++ b/fs/nfsd/xdr3.h
> @@ -152,7 +152,7 @@ struct nfsd3_writeres {
>  	__be32			status;
>  	struct svc_fh		fh;
>  	unsigned long		count;
> -	int			committed;
> +	u32			committed;
>  	__be32			verf[2];
>  };
>  

After looking at this more closely and talking it over with Chuck,
self-NAK on this patch. It's not clear to me that it's safe to
downgrade a SYNC write to an UNSTABLE one.

FWIW, the spec does seem to require it in this case: RFC 1813 section
3.3.7 says the server MUST set committed to UNSTABLE if it didn't
commit to stable storage, which it clearly didn't do in this case.

The problem is that it's not clear to me that the clients would be
prepared to issue a COMMIT in those cases. Since this only affects
(insane) people using the "async" export option, I think we can safely
just drop this one.
-- 
Jeff Layton <[email protected]>