On Fri, Sep 11, 2020 at 07:31:58AM -0400, Brian Foster wrote: > On Thu, Sep 10, 2020 at 03:48:42PM -0700, 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 > > 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 > > 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. > > > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > --- > > v2: define what is a V4 filesystem, update the administrator guide > > --- > > Seems reasonable to me... > > > Documentation/admin-guide/xfs.rst | 20 ++++++++++++++++++++ > > fs/xfs/Kconfig | 23 +++++++++++++++++++++++ > > fs/xfs/xfs_mount.c | 11 +++++++++++ > > 3 files changed, 54 insertions(+) > > > > diff --git a/Documentation/admin-guide/xfs.rst b/Documentation/admin-guide/xfs.rst > > index f461d6c33534..68d69733a1df 100644 > > --- a/Documentation/admin-guide/xfs.rst > > +++ b/Documentation/admin-guide/xfs.rst > > @@ -210,6 +210,25 @@ 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 the string "crc=0" is found, or no "crc=" string is found, > > +the filesystem is a V4 filesystem. > > + > > +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. > > > > Deprecated Mount Options > > ======================== > > @@ -217,6 +236,7 @@ Deprecated Mount Options > > =========================== ================ > > Name Removal Schedule > > =========================== ================ > > +Mounting with V4 filesystem September 2030 > > =========================== ================ > > > > > > diff --git a/fs/xfs/Kconfig b/fs/xfs/Kconfig > > index e685299eb3d2..5970d0f77db9 100644 > > --- a/fs/xfs/Kconfig > > +++ b/fs/xfs/Kconfig > > @@ -22,6 +22,29 @@ 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, or no "crc=" > > + string is found, the filesystem is a V4 filesystem. > > + > > + 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_mount.c b/fs/xfs/xfs_mount.c > > index ed69c4bfda71..3678dfeecd64 100644 > > --- a/fs/xfs/xfs_mount.c > > +++ b/fs/xfs/xfs_mount.c > > @@ -315,6 +315,17 @@ xfs_readsb( > > goto release_buf; > > } > > > > +#ifndef CONFIG_XFS_SUPPORT_V4 > > + /* V4 support is undergoing deprecation. */ > > + if (!xfs_sb_version_hascrc(sbp)) { > > + if (loud) > > + xfs_warn(mp, > > + "Deprecated V4 format (crc=0) not supported by kernel."); > > + error = -EINVAL; > > + goto release_buf; > > + } > > +#endif > > + > > Should we not have a (oneshot?) warning for systems that choose to > continue to support and use v4 filesystems? ISTM that's the best way to > ensure there's feedback on this change earlier rather than later, or > otherwise encourage such users to reformat with v5 at the next available > opportunity... hm, yes. > BTW, any reason this is in xfs_readsb() vs. xfs_fc_fill_super() where we > have various other version/feature checks and warnings? no particular reason. i like the idea of moving this chunk over there. --d > Brian > > > /* > > * We must be able to do sector-sized and sector-aligned IO. > > */ > > >