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From: Dave Chinner <david@fromorbit.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>,
	linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH v2 04/12] fat: only specify I_DIRTY_TIME when needed in fat_update_time()
Date: Tue, 12 Jan 2021 16:21:14 +1100	[thread overview]
Message-ID: <20210112052114.GS331610@dread.disaster.area> (raw)
In-Reply-To: <X/ysA8PuJ/+JXQYL@sol.localdomain>

On Mon, Jan 11, 2021 at 11:50:27AM -0800, Eric Biggers wrote:
> On Mon, Jan 11, 2021 at 11:52:01AM +0100, Christoph Hellwig wrote:
> > On Fri, Jan 08, 2021 at 11:58:55PM -0800, Eric Biggers wrote:
> > > +	if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
> > > +		dirty_flags |= I_DIRTY_SYNC;
> > 
> > fat does not support i_version updates, so this bit can be skipped.
> 
> Is that really the case?  Any filesystem (including fat) can be mounted with
> "iversion", which causes SB_I_VERSION to be set.

That's a bug. Filesystems taht don't support persistent i_version on
disk need to clear SB_I_VERSION in their mount and remount paths
because the VFS iversion mount option was a complete screwup from
the start.

> A lot of filesystems (including fat) don't store i_version to disk, but it looks
> like it will still get updated in-memory.  Could anything be relying on that?

If they do, then they are broken by definition. i_version as
reported to observers is defined as monotonically increasing with
every change to the inode. i.e. it never goes backwards. Which, of
course, it will do if you crash or even just unmount/mount a
filesystem that doesn't persist it.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

WARNING: multiple messages have this Message-ID
From: Dave Chinner <david@fromorbit.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>,
	linux-f2fs-devel@lists.sourceforge.net,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-ext4@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [f2fs-dev] [PATCH v2 04/12] fat: only specify I_DIRTY_TIME when needed in fat_update_time()
Date: Tue, 12 Jan 2021 16:21:14 +1100	[thread overview]
Message-ID: <20210112052114.GS331610@dread.disaster.area> (raw)
In-Reply-To: <X/ysA8PuJ/+JXQYL@sol.localdomain>

On Mon, Jan 11, 2021 at 11:50:27AM -0800, Eric Biggers wrote:
> On Mon, Jan 11, 2021 at 11:52:01AM +0100, Christoph Hellwig wrote:
> > On Fri, Jan 08, 2021 at 11:58:55PM -0800, Eric Biggers wrote:
> > > +	if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
> > > +		dirty_flags |= I_DIRTY_SYNC;
> > 
> > fat does not support i_version updates, so this bit can be skipped.
> 
> Is that really the case?  Any filesystem (including fat) can be mounted with
> "iversion", which causes SB_I_VERSION to be set.

That's a bug. Filesystems taht don't support persistent i_version on
disk need to clear SB_I_VERSION in their mount and remount paths
because the VFS iversion mount option was a complete screwup from
the start.

> A lot of filesystems (including fat) don't store i_version to disk, but it looks
> like it will still get updated in-memory.  Could anything be relying on that?

If they do, then they are broken by definition. i_version as
reported to observers is defined as monotonically increasing with
every change to the inode. i.e. it never goes backwards. Which, of
course, it will do if you crash or even just unmount/mount a
filesystem that doesn't persist it.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com


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  reply	other threads:[~2021-01-12  5:22 UTC|newest]

Thread overview: 82+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-09  7:58 [PATCH v2 00/12] lazytime fix and cleanups Eric Biggers
2021-01-09  7:58 ` [f2fs-dev] " Eric Biggers
2021-01-09  7:58 ` [PATCH v2 01/12] fs: fix lazytime expiration handling in __writeback_single_inode() Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 10:48   ` Christoph Hellwig
2021-01-11 10:48     ` [f2fs-dev] " Christoph Hellwig
2021-01-11 14:46   ` Jan Kara
2021-01-11 14:46     ` [f2fs-dev] " Jan Kara
2021-01-09  7:58 ` [PATCH v2 02/12] fs: correctly document the inode dirty flags Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 14:48   ` Jan Kara
2021-01-11 14:48     ` [f2fs-dev] " Jan Kara
2021-01-09  7:58 ` [PATCH v2 03/12] fs: only specify I_DIRTY_TIME when needed in generic_update_time() Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 14:50   ` Jan Kara
2021-01-11 14:50     ` [f2fs-dev] " Jan Kara
2021-01-09  7:58 ` [PATCH v2 04/12] fat: only specify I_DIRTY_TIME when needed in fat_update_time() Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 10:52   ` Christoph Hellwig
2021-01-11 10:52     ` [f2fs-dev] " Christoph Hellwig
2021-01-11 19:50     ` Eric Biggers
2021-01-11 19:50       ` [f2fs-dev] " Eric Biggers
2021-01-12  5:21       ` Dave Chinner [this message]
2021-01-12  5:21         ` Dave Chinner
2021-01-12 13:23       ` Christoph Hellwig
2021-01-12 13:23         ` [f2fs-dev] " Christoph Hellwig
2021-01-11 14:52   ` Jan Kara
2021-01-11 14:52     ` [f2fs-dev] " Jan Kara
2021-01-09  7:58 ` [PATCH v2 05/12] fs: don't call ->dirty_inode for lazytime timestamp updates Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 14:54   ` Jan Kara
2021-01-11 14:54     ` [f2fs-dev] " Jan Kara
2021-01-09  7:58 ` [PATCH v2 06/12] fs: pass only I_DIRTY_INODE flags to ->dirty_inode Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 14:56   ` Jan Kara
2021-01-11 14:56     ` [f2fs-dev] " Jan Kara
2021-01-09  7:58 ` [PATCH v2 07/12] fs: clean up __mark_inode_dirty() a bit Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 14:59   ` Jan Kara
2021-01-11 14:59     ` [f2fs-dev] " Jan Kara
2021-01-09  7:58 ` [PATCH v2 08/12] fs: drop redundant check from __writeback_single_inode() Eric Biggers
2021-01-09  7:58   ` [f2fs-dev] " Eric Biggers
2021-01-11 10:52   ` Christoph Hellwig
2021-01-11 10:52     ` [f2fs-dev] " Christoph Hellwig
2021-01-11 15:00   ` Jan Kara
2021-01-11 15:00     ` [f2fs-dev] " Jan Kara
2021-01-09  7:59 ` [PATCH v2 09/12] fs: improve comments for writeback_single_inode() Eric Biggers
2021-01-09  7:59   ` [f2fs-dev] " Eric Biggers
2021-01-11 10:53   ` Christoph Hellwig
2021-01-11 10:53     ` [f2fs-dev] " Christoph Hellwig
2021-01-11 15:05   ` Jan Kara
2021-01-11 15:05     ` [f2fs-dev] " Jan Kara
2021-01-09  7:59 ` [PATCH v2 10/12] gfs2: don't worry about I_DIRTY_TIME in gfs2_fsync() Eric Biggers
2021-01-09  7:59   ` [f2fs-dev] " Eric Biggers
2021-01-11 15:06   ` Jan Kara
2021-01-11 15:06     ` [f2fs-dev] " Jan Kara
2021-01-09  7:59 ` [PATCH v2 11/12] ext4: simplify i_state checks in __ext4_update_other_inode_time() Eric Biggers
2021-01-09  7:59   ` [f2fs-dev] " Eric Biggers
2021-01-11 10:53   ` Christoph Hellwig
2021-01-11 10:53     ` [f2fs-dev] " Christoph Hellwig
2021-01-11 20:23     ` Eric Biggers
2021-01-11 20:23       ` [f2fs-dev] " Eric Biggers
2021-01-12 13:25       ` Christoph Hellwig
2021-01-12 13:25         ` [f2fs-dev] " Christoph Hellwig
2021-02-03  5:16         ` Theodore Ts'o
2021-02-03  5:16           ` [f2fs-dev] " Theodore Ts'o
2021-01-11 15:11   ` Jan Kara
2021-01-11 15:11     ` [f2fs-dev] " Jan Kara
2021-01-09  7:59 ` [PATCH v2 12/12] xfs: remove a stale comment from xfs_file_aio_write_checks() Eric Biggers
2021-01-09  7:59   ` [f2fs-dev] " Eric Biggers
2021-01-12 17:31   ` Darrick J. Wong
2021-01-12 17:31     ` [f2fs-dev] " Darrick J. Wong
2021-01-11 15:15 ` [PATCH v2 00/12] lazytime fix and cleanups Jan Kara
2021-01-11 15:15   ` [f2fs-dev] " Jan Kara
2021-01-11 20:44   ` Eric Biggers
2021-01-11 20:44     ` [f2fs-dev] " Eric Biggers
2021-02-03  5:11     ` Theodore Ts'o
2021-02-03  5:11       ` [f2fs-dev] " Theodore Ts'o
2021-02-03  5:22       ` Eric Biggers
2021-02-03  5:22         ` [f2fs-dev] " Eric Biggers
2021-02-03 15:49         ` Theodore Ts'o
2021-02-03 15:49           ` [f2fs-dev] " Theodore Ts'o

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