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Dave Chinner e23b55d537 xfs: rework attr2 feature and mount options
The attr2 feature is somewhat unique in that it has both a superblock
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
reconciliation had a bug where it ignored the noattr2 mount option.

For reasons lost to the mists of time, it was decided that resolving
this issue in commit 7c12f29650 ("[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.

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 all times and it cannot be disabled.  i.e. the noattr2
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.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
2021-08-19 10:07:11 -07:00
arch powerpc fixes for 5.14 #4 2021-08-01 12:18:44 -07:00
block block-5.14-2021-07-30 2021-07-30 11:08:12 -07:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-07-09 11:00:44 -07:00
Documentation ARM: 2021-07-29 09:42:09 -07:00
drivers Networking fixes for 5.14-rc4, including fixes from bpf, can, WiFi (mac80211) 2021-07-30 16:01:36 -07:00
fs xfs: rework attr2 feature and mount options 2021-08-19 10:07:11 -07:00
include mm: Add kvrealloc() 2021-08-09 15:57:43 -07:00
init Revert "mm/slub: use stackdepot to save stack trace in objects" 2021-07-17 13:27:00 -07:00
ipc Merge branch 'akpm' (patches from Andrew) 2021-07-02 12:08:10 -07:00
kernel Networking fixes for 5.14-rc4, including fixes from bpf, can, WiFi (mac80211) 2021-07-30 16:01:36 -07:00
lib lib/test_string.c: move string selftest in the Runtime Testing menu 2021-07-30 10:14:39 -07:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: Add kvrealloc() 2021-08-09 15:57:43 -07:00
net Networking fixes for 5.14-rc4, including fixes from bpf, can, WiFi (mac80211) 2021-07-30 16:01:36 -07:00
samples Networking fixes for 5.14-rc2, including fixes from bpf and netfilter. 2021-07-14 09:24:32 -07:00
scripts Kbuild fixes for v5.14 2021-07-18 11:10:30 -07:00
security asm-generic/unaligned: Unify asm/unaligned.h around struct helper 2021-07-02 12:43:40 -07:00
sound sound fixes for 5.14-rc3 2021-07-23 09:58:23 -07:00
tools perf tools fixes for v5.14: 2nd batch 2021-08-01 12:25:30 -07:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: add missing compat KVM_CLEAR_DIRTY_LOG 2021-07-27 16:59:01 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap m68k updates for v5.14 2021-06-28 14:01:03 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Networking fixes for 5.14-rc4, including fixes from bpf, can, WiFi (mac80211) 2021-07-30 16:01:36 -07:00
Makefile Linux 5.14-rc4 2021-08-01 17:04:17 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.