Re: [PATCH 2/2] nfsd: Record NFSv4 pre/post-op attributes as non-atomic

[bfields@fieldses.org (J. Bruce Fields)]

On Mon, Nov 30, 2020 at 11:14:27PM -0500, trondmy@kernel.org wrote:
> From: Trond Myklebust <trond.myklebust@hammerspace.com>
> 
> For the case of NFSv4, specify to the client that the the pre/post-op
> attributes were not recorded atomically with the main operation.
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  fs/nfs/export.c          | 3 ++-
>  fs/nfsd/nfsfh.c          | 4 ++++
>  fs/nfsd/nfsfh.h          | 5 +++++
>  fs/nfsd/xdr4.h           | 2 +-
>  include/linux/exportfs.h | 3 +++
>  5 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/export.c b/fs/nfs/export.c
> index 48b879cfe6e3..7412bb164fa7 100644
> --- a/fs/nfs/export.c
> +++ b/fs/nfs/export.c
> @@ -172,5 +172,6 @@ const struct export_operations nfs_export_ops = {
>  	.fh_to_dentry = nfs_fh_to_dentry,
>  	.get_parent = nfs_get_parent,
>  	.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|
> -		EXPORT_OP_CLOSE_BEFORE_UNLINK|EXPORT_OP_REMOTE_FS,
> +		EXPORT_OP_CLOSE_BEFORE_UNLINK|EXPORT_OP_REMOTE_FS|
> +		EXPORT_OP_NOATOMIC_ATTR,

So I still don't understand why we need a new flag for this.

Before you said it was because a filesystem might want to turn off the
v4 atomic flag but still return v3 post-wcc attributes.

But it seems that a) we have no example of a filesystem that wants to do
that, b) it would violate the protocol anyway.

Is that right?

If so, then let's just stick to one flag for both.

--b.

>  };
> diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> index e80a7525561d..66f2ef67792a 100644
> --- a/fs/nfsd/nfsfh.c
> +++ b/fs/nfsd/nfsfh.c
> @@ -301,6 +301,10 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp)
>  	fhp->fh_export = exp;
>  
>  	switch (rqstp->rq_vers) {
> +	case 4:
> +		if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOATOMIC_ATTR)
> +			fhp->fh_no_atomic_attr = true;
> +		break;
>  	case 3:
>  		if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOWCC)
>  			fhp->fh_no_wcc = true;
> diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
> index 347d10aa6265..cb20c2cd3469 100644
> --- a/fs/nfsd/nfsfh.h
> +++ b/fs/nfsd/nfsfh.h
> @@ -36,6 +36,11 @@ typedef struct svc_fh {
>  	bool			fh_locked;	/* inode locked by us */
>  	bool			fh_want_write;	/* remount protection taken */
>  	bool			fh_no_wcc;	/* no wcc data needed */
> +	bool			fh_no_atomic_attr;
> +						/*
> +						 * wcc data is not atomic with
> +						 * operation
> +						 */
>  	int			fh_flags;	/* FH flags */
>  #ifdef CONFIG_NFSD_V3
>  	bool			fh_post_saved;	/* post-op attrs saved */
> diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
> index b4556e86e97c..a60ff5ce1a37 100644
> --- a/fs/nfsd/xdr4.h
> +++ b/fs/nfsd/xdr4.h
> @@ -748,7 +748,7 @@ static inline void
>  set_change_info(struct nfsd4_change_info *cinfo, struct svc_fh *fhp)
>  {
>  	BUG_ON(!fhp->fh_pre_saved);
> -	cinfo->atomic = (u32)fhp->fh_post_saved;
> +	cinfo->atomic = (u32)(fhp->fh_post_saved && !fhp->fh_no_atomic_attr);
>  
>  	cinfo->before_change = fhp->fh_pre_change;
>  	cinfo->after_change = fhp->fh_post_change;
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index d93e8a6737bb..9f4d4bcbf251 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -217,6 +217,9 @@ struct export_operations {
>  #define	EXPORT_OP_NOSUBTREECHK		(0x2) /* no subtree checking */
>  #define	EXPORT_OP_CLOSE_BEFORE_UNLINK	(0x4) /* close files before unlink */
>  #define EXPORT_OP_REMOTE_FS		(0x8) /* Filesystem is remote */
> +#define EXPORT_OP_NOATOMIC_ATTR		(0x10) /* Filesystem cannot supply
> +						  atomic attribute updates
> +						*/
>  	unsigned long	flags;
>  };
>  
> -- 
> 2.28.0