On 9/11/20 11:43 AM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> The V4 filesystem format contains known weaknesses in the on-disk format
> that make metadata verification diffiult. In addition, the format will
Editorial nitpicks you are free to take or leave:
drop "will"
> does not support dates past 2038 and will not be upgraded to do so.
> Therefore, we should start the process of retiring the old format to
> close off attack surfaces and to encourage users to migrate onto V5.
>
> Therefore, make XFS V4 support a configurable option. For the first
Too many "Therefores":
"This patch makes XFS V4 support a ..."
> period it will be default Y in case some distributors want to withdraw
> support early; for the second period it will be default N so that anyone
> who wishes to continue support can do so; and after that, support will
> be removed from the kernel.
Maybe something like:
"Dates for these events are added to the XFS documentation in the kernel."
In any case,
Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
> v3: be a little more helpful about old xfsprogs and warn more loudly
> about deprecation
> v2: define what is a V4 filesystem, update the administrator guide
> ---
> Documentation/admin-guide/xfs.rst | 23 +++++++++++++++++++++++
> fs/xfs/Kconfig | 24 ++++++++++++++++++++++++
> fs/xfs/xfs_super.c | 13 +++++++++++++
> 3 files changed, 60 insertions(+)
>
> diff --git a/Documentation/admin-guide/xfs.rst b/Documentation/admin-guide/xfs.rst
> index f461d6c33534..b6deea9ec073 100644
> --- a/Documentation/admin-guide/xfs.rst
> +++ b/Documentation/admin-guide/xfs.rst
> @@ -210,6 +210,28 @@ When mounting an XFS filesystem, the following options are accepted.
> inconsistent namespace presentation during or after a
> failover event.
>
> +Deprecation of V4 Format
> +========================
> +
> +The V4 filesystem format lacks certain features that are supported by
> +the V5 format, such as metadata checksumming, strengthened metadata
> +verification, and the ability to store timestamps past the year 2038.
> +Because of this, the V4 format is deprecated. All users should upgrade
> +by backing up their files, reformatting, and restoring from the backup.
> +
> +Administrators and users can detect a V4 filesystem by running xfs_info
> +against a filesystem mountpoint and checking for a string beginning with
> +"crc=". If no such string is found, please upgrade xfsprogs to the
> +latest version and try again.
> +
> +The deprecation will take place in two parts. Support for mounting V4
> +filesystems can now be disabled at kernel build time via Kconfig option.
> +The option will default to yes until September 2025, at which time it
> +will be changed to default to no. In September 2030, support will be
> +removed from the codebase entirely.
> +
> +Note: Distributors may choose to withdraw V4 format support earlier than
> +the dates listed above.
>
> Deprecated Mount Options
> ========================
> @@ -217,6 +239,7 @@ Deprecated Mount Options
> =========================== ================
> Name Removal Schedule
> =========================== ================
> +Mounting with V4 filesystem September 2030
> =========================== ================
>
>
> diff --git a/fs/xfs/Kconfig b/fs/xfs/Kconfig
> index e685299eb3d2..5422227e9e93 100644
> --- a/fs/xfs/Kconfig
> +++ b/fs/xfs/Kconfig
> @@ -22,6 +22,30 @@ config XFS_FS
> system of your root partition is compiled as a module, you'll need
> to use an initial ramdisk (initrd) to boot.
>
> +config XFS_SUPPORT_V4
> + bool "Support deprecated V4 (crc=0) format"
> + default y
> + help
> + The V4 filesystem format lacks certain features that are supported
> + by the V5 format, such as metadata checksumming, strengthened
> + metadata verification, and the ability to store timestamps past the
> + year 2038. Because of this, the V4 format is deprecated. All users
> + should upgrade by backing up their files, reformatting, and restoring
> + from the backup.
> +
> + Administrators and users can detect a V4 filesystem by running
> + xfs_info against a filesystem mountpoint and checking for a string
> + beginning with "crc=". If the string "crc=0" is found, the
> + filesystem is a V4 filesystem. If no such string is found, please
> + upgrade xfsprogs to the latest version and try again.
> +
> + This option will become default N in September 2025. Support for the
> + V4 format will be removed entirely in September 2030. Distributors
> + can say N here to withdraw support earlier.
> +
> + To continue supporting the old V4 format (crc=0), say Y.
> + To close off an attack surface, say N.
> +
> config XFS_QUOTA
> bool "XFS Quota support"
> depends on XFS_FS
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index febd61ba071d..e2250c6d7251 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1451,6 +1451,19 @@ xfs_fc_fill_super(
> if (error)
> goto out_free_sb;
>
> + /* V4 support is undergoing deprecation. */
> + if (!xfs_sb_version_hascrc(&mp->m_sb)) {
> +#ifdef CONFIG_XFS_SUPPORT_V4
> + xfs_warn_once(mp,
> + "Deprecated V4 format (crc=0) will not be supported after September 2030.");
> +#else
> + xfs_warn(mp,
> + "Deprecated V4 format (crc=0) not supported by kernel.");
> + error = -EINVAL;
> + goto out_free_sb;
> +#endif
> + }
> +
> /*
> * XFS block mappings use 54 bits to store the logical block offset.
> * This should suffice to handle the maximum file size that the VFS
>
