Re: [PATCH 1/2 v2] nfs: use change attribute for NFS re-exports

Chuck Lever
2021-01-29T20:47:30Z

Hi Bruce-

> On Jan 29, 2021, at 2:26 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
>
> From: "J. Bruce Fields" <bfields@redhat.com>
>
> When exporting NFS, we may as well use the real change attribute
> returned by the original server instead of faking up a change attribute
> from the ctime.
>
> Note we can't do that by setting I_VERSION--that would also turn on the
> logic in iversion.h which treats the lower bit specially, and that
> doesn't make sense for NFS.
>
> So instead we define a new export operation for filesystems like NFS
> that want to manage the change attribute themselves.
>
> Signed-off-by: J. Bruce Fields <bfields@redhat.com>

These two patches have replaced the v1 patches from last week in
the for-next branch at

git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git

These are included provisionally while review and further testing
is ongoing.

> ---
> fs/nfs/export.c | 18 ++++++++++++++++++
> fs/nfsd/nfsfh.h | 5 ++++-
> include/linux/exportfs.h | 1 +
> 3 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfs/export.c b/fs/nfs/export.c
> index 7412bb164fa7..f2b34cfe286c 100644
> --- a/fs/nfs/export.c
> +++ b/fs/nfs/export.c
> @@ -167,10 +167,28 @@ nfs_get_parent(struct dentry *dentry)
> return parent;
> }
>
> +static u64 nfs_fetch_iversion(struct inode *inode)
> +{
> + struct nfs_server *server = NFS_SERVER(inode);
> +
> + /* Is this the right call?: */
> + nfs_revalidate_inode(server, inode);
> + /*
> + * Also, note we're ignoring any returned error. That seems to be
> + * the practice for cache consistency information elsewhere in
> + * the server, but I'm not sure why.
> + */
> + if (server->nfs_client->rpc_ops->version >= 4)
> + return inode_peek_iversion_raw(inode);
> + else
> + return time_to_chattr(&inode->i_ctime);
> +}
> +
> const struct export_operations nfs_export_ops = {
> .encode_fh = nfs_encode_fh,
> .fh_to_dentry = nfs_fh_to_dentry,
> .get_parent = nfs_get_parent,
> + .fetch_iversion = nfs_fetch_iversion,
> .flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|
> EXPORT_OP_CLOSE_BEFORE_UNLINK|EXPORT_OP_REMOTE_FS|
> EXPORT_OP_NOATOMIC_ATTR,
> diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
> index cb20c2cd3469..f58933519f38 100644
> --- a/fs/nfsd/nfsfh.h
> +++ b/fs/nfsd/nfsfh.h
> @@ -12,6 +12,7 @@
> #include <linux/sunrpc/svc.h>
> #include <uapi/linux/nfsd/nfsfh.h>
> #include <linux/iversion.h>
> +#include <linux/exportfs.h>
>
> static inline __u32 ino_t_to_u32(ino_t ino)
> {
> @@ -264,7 +265,9 @@ fh_clear_wcc(struct svc_fh *fhp)
> static inline u64 nfsd4_change_attribute(struct kstat *stat,
> struct inode *inode)
> {
> - if (IS_I_VERSION(inode)) {
> + if (inode->i_sb->s_export_op->fetch_iversion)
> + return inode->i_sb->s_export_op->fetch_iversion(inode);
> + else if (IS_I_VERSION(inode)) {
> u64 chattr;
>
> chattr = stat->ctime.tv_sec;
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index 9f4d4bcbf251..fe848901fcc3 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -213,6 +213,7 @@ struct export_operations {
> bool write, u32 *device_generation);
> int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
> int nr_iomaps, struct iattr *iattr);
> + u64 (*fetch_iversion)(struct inode *);
> #define EXPORT_OP_NOWCC (0x1) /* don't collect v3 wcc data */
> #define EXPORT_OP_NOSUBTREECHK (0x2) /* no subtree checking */
> #define EXPORT_OP_CLOSE_BEFORE_UNLINK (0x4) /* close files before unlink */
> --
> 2.29.2
>

--
Chuck Lever