On Fri, 2020-11-20 at 17:39 -0500, J. Bruce Fields wrote:
> From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
>
> After this, only filesystems lacking change attribute support will leave
> the fetch_iversion export op NULL.
>
> This seems cleaner to me, and will allow some minor optimizations in the
> nfsd code.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> ---
> fs/btrfs/export.c | 2 ++
> fs/ext4/super.c | 9 +++++++++
> fs/nfsd/nfs4xdr.c | 2 +-
> fs/nfsd/nfsfh.h | 25 +++----------------------
> fs/nfsd/xdr4.h | 4 +++-
> fs/xfs/xfs_export.c | 2 ++
> include/linux/iversion.h | 26 ++++++++++++++++++++++++++
> 7 files changed, 46 insertions(+), 24 deletions(-)
>
> diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
> index 1a8d419d9e1f..ece32440999a 100644
> --- a/fs/btrfs/export.c
> +++ b/fs/btrfs/export.c
> @@ -7,6 +7,7 @@
> #include "btrfs_inode.h"
> #include "print-tree.h"
> #include "export.h"
> +#include <linux/iversion.h>
>
>
> #define BTRFS_FID_SIZE_NON_CONNECTABLE (offsetof(struct btrfs_fid, \
> parent_objectid) / 4)
> @@ -279,4 +280,5 @@ const struct export_operations btrfs_export_ops = {
> .fh_to_parent = btrfs_fh_to_parent,
> .get_parent = btrfs_get_parent,
> .get_name = btrfs_get_name,
> + .fetch_iversion = generic_fetch_iversion,
> };
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index ef4734b40e2a..a4f48273d435 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1685,11 +1685,20 @@ static const struct super_operations ext4_sops = {
> .bdev_try_to_free_page = bdev_try_to_free_page,
> };
>
>
> +static u64 ext4_fetch_iversion(struct inode *inode)
> +{
> + if (IS_I_VERSION(inode))
> + return generic_fetch_iversion(inode);
> + else
> + return time_to_chattr(&inode->i_ctime);
> +}
> +
> static const struct export_operations ext4_export_ops = {
> .fh_to_dentry = ext4_fh_to_dentry,
> .fh_to_parent = ext4_fh_to_parent,
> .get_parent = ext4_get_parent,
> .commit_metadata = ext4_nfs_commit_metadata,
> + .fetch_iversion = ext4_fetch_iversion,
> };
>
>
> enum {
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index 18c912930947..182190684792 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -3187,7 +3187,7 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
> p = xdr_reserve_space(xdr, 4);
> if (!p)
> goto out_resource;
> - if (IS_I_VERSION(d_inode(dentry)))
> + if (IS_I_VERSION(d_inode(dentry))
> *p++ = cpu_to_be32(NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR);
> else
> *p++ = cpu_to_be32(NFS4_CHANGE_TYPE_IS_TIME_METADATA);
> diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
> index 2656a3464c6c..ac3e309d7339 100644
> --- a/fs/nfsd/nfsfh.h
> +++ b/fs/nfsd/nfsfh.h
> @@ -46,8 +46,8 @@ typedef struct svc_fh {
> struct timespec64 fh_pre_mtime; /* mtime before oper */
> struct timespec64 fh_pre_ctime; /* ctime before oper */
> /*
> - * pre-op nfsv4 change attr: note must check IS_I_VERSION(inode)
> - * to find out if it is valid.
> + * pre-op nfsv4 change attr: note must check for fetch_iversion
> + * op to find out if it is valid.
> */
> u64 fh_pre_change;
>
>
> @@ -246,31 +246,12 @@ fh_clear_wcc(struct svc_fh *fhp)
> fhp->fh_pre_saved = false;
> }
>
>
> -/*
> - * We could use i_version alone as the change attribute. However,
> - * i_version can go backwards after a reboot. On its own that doesn't
> - * necessarily cause a problem, but if i_version goes backwards and then
> - * is incremented again it could reuse a value that was previously used
> - * before boot, and a client who queried the two values might
> - * incorrectly assume nothing changed.
> - *
> - * By using both ctime and the i_version counter we guarantee that as
> - * long as time doesn't go backwards we never reuse an old value.
> - */
> static inline u64 nfsd4_change_attribute(struct kstat *stat,
> struct inode *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;
> - chattr <<= 30;
> - chattr += stat->ctime.tv_nsec;
> - chattr += inode_query_iversion(inode);
> - return chattr;
> - } else
> + else
> return time_to_chattr(&stat->ctime);
> }
>
>
> diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
> index 9c2d942d055d..f0c8fbe704a2 100644
> --- a/fs/nfsd/xdr4.h
> +++ b/fs/nfsd/xdr4.h
> @@ -761,10 +761,12 @@ void warn_on_nonidempotent_op(struct nfsd4_op *op);
> static inline void
> set_change_info(struct nfsd4_change_info *cinfo, struct svc_fh *fhp)
> {
> + struct inode *inode = d_inode(fhp->fh_dentry);
> +
> BUG_ON(!fhp->fh_pre_saved);
> cinfo->atomic = (u32)fhp->fh_post_saved;
>
>
> - if (IS_I_VERSION(d_inode(fhp->fh_dentry))) {
> + if (inode->i_sb->s_export_op->fetch_iversion) {
> cinfo->before_change = fhp->fh_pre_change;
> cinfo->after_change = fhp->fh_post_change;
> } else {
> diff --git a/fs/xfs/xfs_export.c b/fs/xfs/xfs_export.c
> index 465fd9e048d4..b950fac3d7df 100644
> --- a/fs/xfs/xfs_export.c
> +++ b/fs/xfs/xfs_export.c
> @@ -16,6 +16,7 @@
> #include "xfs_inode_item.h"
> #include "xfs_icache.h"
> #include "xfs_pnfs.h"
> +#include <linux/iversion.h>
>
>
> /*
> * Note that we only accept fileids which are long enough rather than allow
> @@ -234,4 +235,5 @@ const struct export_operations xfs_export_operations = {
> .map_blocks = xfs_fs_map_blocks,
> .commit_blocks = xfs_fs_commit_blocks,
> #endif
> + .fetch_iversion = generic_fetch_iversion,
> };
> diff --git a/include/linux/iversion.h b/include/linux/iversion.h
> index 3bfebde5a1a6..ded74523c8a6 100644
> --- a/include/linux/iversion.h
> +++ b/include/linux/iversion.h
> @@ -328,6 +328,32 @@ inode_query_iversion(struct inode *inode)
> return cur >> I_VERSION_QUERIED_SHIFT;
> }
>
>
> +/*
> + * We could use i_version alone as the NFSv4 change attribute. However,
> + * i_version can go backwards after a reboot. On its own that doesn't
> + * necessarily cause a problem, but if i_version goes backwards and then
> + * is incremented again it could reuse a value that was previously used
> + * before boot, and a client who queried the two values might
> + * incorrectly assume nothing changed.
> + *
> + * By using both ctime and the i_version counter we guarantee that as
> + * long as time doesn't go backwards we never reuse an old value.
> + *
> + * A filesystem that has an on-disk boot counter or similar might prefer
> + * to use that to avoid the risk of the change attribute going backwards
> + * if system time is set backwards.
> + */
> +static inline u64 generic_fetch_iversion(struct inode *inode)
> +{
> + u64 chattr;
> +
> + chattr = inode->i_ctime.tv_sec;
> + chattr <<= 30;
> + chattr += inode->i_ctime.tv_nsec;
> + chattr += inode_query_iversion(inode);
> + return chattr;
> +}
> +
> /*
> * For filesystems without any sort of change attribute, the best we can
> * do is fake one up from the ctime:
One more nit:
We probably don't want anyone using this on filesystems that don't set
SB_I_VERSION. It might be a good idea to add something like:
WARN_ON_ONCE(!IS_I_VERSION(inode));
To this function, to catch anyone trying to do it.
--
Jeff Layton <jlayton@xxxxxxxxxx>
