On Wed, Jul 14, 2021 at 02:18:59PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> The attr2 feature is someone unique in that it has both a superblock
s/someone/somewhat/
> feature bit to enable it and mount options to enable and disable it.
>
> Back when it was first introduced in 2005, attr2 was disabled unless
> either the attr2 superblock feature bit was set, or the attr2 mount
> option was set. If the superblock feature bit was not set but the
> mount option was set, then when the first attr2 format inode fork
> was created, it would set the superblock feature bit. This is as it
> should be - the superblock feature bit indicated the presence of the
> attr2 on disk format.
>
> The noattr2 mount option, however, did not affect the superblock
> feature bit. If noattr2 was specified, the on-disk superblock
> feature bit was ignored and the code always just created attr1
> format inode forks. If neither of the attr2 or noattr2 mounts
> option were specified, then the behaviour was determined by the
> superblock feature bit.
>
> This was all pretty sane.
>
> Fast foward 3 years, and we are dealing with fallout from the
> botched sb_features2 addition and having to deal with feature
> mismatches between the sb_features2 and sb_bad_features2 fields. The
> attr2 feature bit was one of these flags. The reconciliation was
> done well after mount option parsing and, unfortunately, the feature
> reconcilliation had a bug where it ignored the noattr2 mount option.
"reconciliation.."
> For reasons lost to the mists of time, it was decided that resolving
> this issue in commit 7c12f296500e ("[XFS] Fix up noattr2 so that it
> will properly update the versionnum and features2 fields.") required
> noattr2 to clear the superblock attr2 feature bit. This greatly
> complicated the attr2 behaviour and broke rules about feature bits
> needing to be set when those specific features are present in the
> filesystem.
Yikes, WTH.
> By complicated, I mean that it introduced problems due to feature
> bit interactions with log recovery. All of the superblock feature
> bit checks are done prior to log recovery, but if we crash after
> removing a feature bit, then on the next mount we see the feature
> bit in the unrecovered superblock, only to have it go away after the
> log has been replayed. This means our mount time feature processing
> could be all wrong.
>
> Hence you can mount with noattr2, crash shortly afterwards, and
> mount again without attr2 or noattr2 and still have attr2 enabled
> because the second mount sees attr2 still enabled in the superblock
> before recovery runs and removes the feature bit. It's just a mess.
>
> Further, this is all legacy code as the v5 format requires attr2 to
> be enabled at al times and it cannot be disabled. i.e. the noattr2
"..at all times..."
> mount option returns an error when used on v5 format filesystems.
>
> To straighten this all out, this patch reverts the attr2/noattr2
> mount option behaviour back to the original behaviour. There is no
> reason for disabling attr2 these days, so we will only do this when
> the noattr2 mount option is set. This will not remove the superblock
> feature bit. The superblock bit will provide the default behaviour
> and only track whether attr2 is present on disk or not. The attr2
> mount option will enable the creation of attr2 format inode forks,
> and if the superblock feature bit is not set it will be added when
> the first attr2 inode fork is created.
...and the whole V4 format is clanking towards deprecation anyway. :)
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
With the commit message fixed up and Christoph's other suggestions
resolved,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
> fs/xfs/libxfs/xfs_format.h | 7 -------
> fs/xfs/xfs_mount.c | 27 ++++++++++-----------------
> fs/xfs/xfs_super.c | 16 +++++++---------
> 3 files changed, 17 insertions(+), 33 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index 76e2461b9e66..a8215bf478b2 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -398,13 +398,6 @@ static inline void xfs_sb_version_addattr2(struct xfs_sb *sbp)
> sbp->sb_features2 |= XFS_SB_VERSION2_ATTR2BIT;
> }
>
> -static inline void xfs_sb_version_removeattr2(struct xfs_sb *sbp)
> -{
> - sbp->sb_features2 &= ~XFS_SB_VERSION2_ATTR2BIT;
> - if (!sbp->sb_features2)
> - sbp->sb_versionnum &= ~XFS_SB_VERSION_MOREBITSBIT;
> -}
> -
> static inline bool xfs_sb_version_hasprojid32bit(struct xfs_sb *sbp)
> {
> return (XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_5) ||
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index d0755494597f..6be2a1c5b0f4 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -607,25 +607,8 @@ xfs_mountfs(
> xfs_warn(mp, "correcting sb_features alignment problem");
> sbp->sb_features2 |= sbp->sb_bad_features2;
> mp->m_update_sb = true;
> -
> - /*
> - * Re-check for ATTR2 in case it was found in bad_features2
> - * slot.
> - */
> - if (xfs_sb_version_hasattr2(&mp->m_sb) &&
> - !(mp->m_flags & XFS_MOUNT_NOATTR2))
> - mp->m_flags |= XFS_MOUNT_ATTR2;
> }
>
> - if (xfs_sb_version_hasattr2(&mp->m_sb) &&
> - (mp->m_flags & XFS_MOUNT_NOATTR2)) {
> - xfs_sb_version_removeattr2(&mp->m_sb);
> - mp->m_update_sb = true;
> -
> - /* update sb_versionnum for the clearing of the morebits */
> - if (!sbp->sb_features2)
> - mp->m_update_sb = true;
> - }
>
> /* always use v2 inodes by default now */
> if (!(mp->m_sb.sb_versionnum & XFS_SB_VERSION_NLINKBIT)) {
> @@ -782,6 +765,16 @@ xfs_mountfs(
> if (error)
> goto out_log_dealloc;
>
> + /*
> + * Now that we've recovered any pending superblock feature bit
> + * additions, we can finish setting up the attr2 behaviour for the
> + * mount. If no attr2 mount options were specified, the we use the
> + * behaviour specified by the superblock feature bit.
> + */
> + if (!(mp->m_flags & (XFS_MOUNT_ATTR2|XFS_MOUNT_NOATTR2)) &&
> + xfs_sb_version_hasattr2(&mp->m_sb))
> + mp->m_flags |= XFS_MOUNT_ATTR2;
> +
> /*
> * Get and sanity-check the root inode.
> * Save the pointer to it in the mount structure.
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 29bec1f6476e..eba25dd4bdb7 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -945,14 +945,6 @@ xfs_finish_flags(
> return -EINVAL;
> }
>
> - /*
> - * mkfs'ed attr2 will turn on attr2 mount unless explicitly
> - * told by noattr2 to turn it off
> - */
> - if (xfs_sb_version_hasattr2(&mp->m_sb) &&
> - !(mp->m_flags & XFS_MOUNT_NOATTR2))
> - mp->m_flags |= XFS_MOUNT_ATTR2;
> -
> /*
> * prohibit r/w mounts of read-only filesystems
> */
> @@ -1288,7 +1280,6 @@ xfs_fs_parse_param(
> return 0;
> case Opt_noattr2:
> xfs_fs_warn_deprecated(fc, param, XFS_MOUNT_NOATTR2, true);
> - parsing_mp->m_flags &= ~XFS_MOUNT_ATTR2;
> parsing_mp->m_flags |= XFS_MOUNT_NOATTR2;
> return 0;
> default:
> @@ -1312,6 +1303,13 @@ xfs_fs_validate_params(
> return -EINVAL;
> }
>
> + if ((mp->m_flags & (XFS_MOUNT_ATTR2|XFS_MOUNT_NOATTR2)) ==
> + (XFS_MOUNT_ATTR2|XFS_MOUNT_NOATTR2)) {
> + xfs_warn(mp, "attr2 and noattr2 cannot both be specified.");
> + return -EINVAL;
> + }
> +
> +
> if ((mp->m_flags & XFS_MOUNT_NOALIGN) &&
> (mp->m_dalign || mp->m_swidth)) {
> xfs_warn(mp,
> --
> 2.31.1
>
