On Mon, 2020-11-30 at 16:24 -0500, trondmy@xxxxxxxxxx wrote:
> From: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
>
> With NFSv3 nfsd will always attempt to send along WCC data to the
> client. This generally involves saving off the in-core inode information
> prior to doing the operation on the given filehandle, and then issuing a
> vfs_getattr to it after the op.
>
> Some filesystems (particularly clustered or networked ones) have an
> expensive ->getattr inode operation. Atomicitiy is also often difficult
> or impossible to guarantee on such filesystems. For those, we're best
> off not trying to provide WCC information to the client at all, and to
> simply allow it to poll for that information as needed with a GETATTR
> RPC.
>
> This patch adds a new flags field to struct export_operations, and
> defines a new EXPORT_OP_NOWCC flag that filesystems can use to indicate
> that nfsd should not attempt to provide WCC info in NFSv3 replies. It
> also adds a blurb about the new flags field and flag to the exporting
> documentation.
>
> The server will also now skip collecting this information for NFSv2 as
> well, since that info is never used there anyway.
>
> Note that this patch does not add this flag to any filesystem
> export_operations structures. This was originally developed to allow
> reexporting nfs via nfsd. That code is not (and may never be) suitable
> for merging into mainline.
>
Probably ought to fix up the above paragraph since we are now merging
this into mainline.
> Other filesystems may want to consider enabling this flag too. It's hard
> to tell however which ones have export operations to enable export via
> knfsd and which ones mostly rely on them for open-by-filehandle support,
> so I'm leaving that up to the individual maintainers to decide. I am
> cc'ing the relevant lists for those filesystems that I think may want to
> consider adding this though.
>
> Cc: HPDD-discuss@xxxxxxxxxxxx
> Cc: ceph-devel@xxxxxxxxxxxxxxx
> Cc: cluster-devel@xxxxxxxxxx
> Cc: fuse-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: ocfs2-devel@xxxxxxxxxxxxxx
> Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
> Signed-off-by: Lance Shelton <lance.shelton@xxxxxxxxxxxxxxx>
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> Documentation/filesystems/nfs/exporting.rst | 27 +++++++++++++++++++++
> fs/nfs/export.c | 1 +
> fs/nfsd/nfs3xdr.c | 7 ++++--
> fs/nfsd/nfsfh.c | 14 +++++++++++
> fs/nfsd/nfsfh.h | 2 +-
> include/linux/exportfs.h | 2 ++
> 6 files changed, 50 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/filesystems/nfs/exporting.rst b/Documentation/filesystems/nfs/exporting.rst
> index 33d588a01ace..a3e3805833d1 100644
> --- a/Documentation/filesystems/nfs/exporting.rst
> +++ b/Documentation/filesystems/nfs/exporting.rst
> @@ -154,6 +154,11 @@ struct which has the following members:
> to find potential names, and matches inode numbers to find the correct
> match.
>
>
>
>
> + flags
> + Some filesystems may need to be handled differently than others. The
> + export_operations struct also includes a flags field that allows the
> + filesystem to communicate such information to nfsd. See the Export
> + Operations Flags section below for more explanation.
>
>
>
>
> A filehandle fragment consists of an array of 1 or more 4byte words,
> together with a one byte "type".
> @@ -163,3 +168,25 @@ generated by encode_fh, in which case it will have been padded with
> nuls. Rather, the encode_fh routine should choose a "type" which
> indicates the decode_fh how much of the filehandle is valid, and how
> it should be interpreted.
> +
> +Export Operations Flags
> +-----------------------
> +In addition to the operation vector pointers, struct export_operations also
> +contains a "flags" field that allows the filesystem to communicate to nfsd
> +that it may want to do things differently when dealing with it. The
> +following flags are defined:
> +
> + EXPORT_OP_NOWCC
> + RFC 1813 recommends that servers always send weak cache consistency
> + (WCC) data to the client after each operation. The server should
> + atomically collect attributes about the inode, do an operation on it,
> + and then collect the attributes afterward. This allows the client to
> + skip issuing GETATTRs in some situations but means that the server
> + is calling vfs_getattr for almost all RPCs. On some filesystems
> + (particularly those that are clustered or networked) this is expensive
> + and atomicity is difficult to guarantee. This flag indicates to nfsd
> + that it should skip providing WCC attributes to the client in NFSv3
> + replies when doing operations on this filesystem. Consider enabling
> + this on filesystems that have an expensive ->getattr inode operation,
> + or when atomicity between pre and post operation attribute collection
> + is impossible to guarantee.
> diff --git a/fs/nfs/export.c b/fs/nfs/export.c
> index 3430d6891e89..8f4c528865c5 100644
> --- a/fs/nfs/export.c
> +++ b/fs/nfs/export.c
> @@ -171,4 +171,5 @@ const struct export_operations nfs_export_ops = {
> .encode_fh = nfs_encode_fh,
> .fh_to_dentry = nfs_fh_to_dentry,
> .get_parent = nfs_get_parent,
> + .flags = EXPORT_OP_NOWCC,
> };
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index 2277f83da250..480342675292 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -206,7 +206,7 @@ static __be32 *
> encode_post_op_attr(struct svc_rqst *rqstp, __be32 *p, struct svc_fh *fhp)
> {
> struct dentry *dentry = fhp->fh_dentry;
> - if (dentry && d_really_is_positive(dentry)) {
> + if (!fhp->fh_no_wcc && dentry && d_really_is_positive(dentry)) {
> __be32 err;
> struct kstat stat;
>
>
>
>
> @@ -261,7 +261,7 @@ void fill_pre_wcc(struct svc_fh *fhp)
> struct kstat stat;
> __be32 err;
>
>
>
>
> - if (fhp->fh_pre_saved)
> + if (fhp->fh_no_wcc || fhp->fh_pre_saved)
> return;
>
>
>
>
> inode = d_inode(fhp->fh_dentry);
> @@ -287,6 +287,9 @@ void fill_post_wcc(struct svc_fh *fhp)
> {
> __be32 err;
>
>
>
>
> + if (fhp->fh_no_wcc)
> + return;
> +
> if (fhp->fh_post_saved)
> printk("nfsd: inode locked twice during operation.\n");
>
>
>
>
> diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> index c81dbbad8792..0c2ee65e46f3 100644
> --- a/fs/nfsd/nfsfh.c
> +++ b/fs/nfsd/nfsfh.c
> @@ -291,6 +291,16 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp)
>
>
>
>
> fhp->fh_dentry = dentry;
> fhp->fh_export = exp;
> +
> + switch (rqstp->rq_vers) {
> + case 3:
> + if (!(dentry->d_sb->s_export_op->flags & EXPORT_OP_NOWCC))
> + break;
> + /* Fallthrough */
> + case 2:
> + fhp->fh_no_wcc = true;
> + }
> +
> return 0;
> out:
> exp_put(exp);
> @@ -559,6 +569,9 @@ fh_compose(struct svc_fh *fhp, struct svc_export *exp, struct dentry *dentry,
> */
> set_version_and_fsid_type(fhp, exp, ref_fh);
>
>
>
>
> + /* If we have a ref_fh, then copy the fh_no_wcc setting from it. */
> + fhp->fh_no_wcc = ref_fh ? ref_fh->fh_no_wcc : false;
> +
> if (ref_fh == fhp)
> fh_put(ref_fh);
>
>
>
>
> @@ -662,6 +675,7 @@ fh_put(struct svc_fh *fhp)
> exp_put(exp);
> fhp->fh_export = NULL;
> }
> + fhp->fh_no_wcc = false;
> return;
> }
>
>
>
>
> diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
> index 56cfbc361561..fb2b60a76b32 100644
> --- a/fs/nfsd/nfsfh.h
> +++ b/fs/nfsd/nfsfh.h
> @@ -35,6 +35,7 @@ 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 */
> int fh_flags; /* FH flags */
> #ifdef CONFIG_NFSD_V3
> bool fh_post_saved; /* post-op attrs saved */
> @@ -54,7 +55,6 @@ typedef struct svc_fh {
> struct kstat fh_post_attr; /* full attrs after operation */
> u64 fh_post_change; /* nfsv4 change; see above */
> #endif /* CONFIG_NFSD_V3 */
> -
> } svc_fh;
> #define NFSD4_FH_FOREIGN (1<<0)
> #define SET_FH_FLAG(c, f) ((c)->fh_flags |= (f))
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index 3ceb72b67a7a..e7de0103a32e 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -213,6 +213,8 @@ struct export_operations {
> bool write, u32 *device_generation);
> int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
> int nr_iomaps, struct iattr *iattr);
> +#define EXPORT_OP_NOWCC (0x1) /* Don't collect wcc data for NFSv3 replies */
> + unsigned long flags;
> };
>
>
>
>
> extern int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
