From: "Theodore Ts'o" <tytso@mit.edu>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-f2fs-devel@lists.sourceforge.net,
Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
linux-fsdevel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] f2fs: remove broken support for allocating DIO writes
Date: Fri, 30 Jul 2021 22:46:16 -0400 [thread overview]
Message-ID: <YQS5eBljtztWwOFE@mit.edu> (raw)
In-Reply-To: <YQRQRh1zUHSIzcC/@gmail.com>
On Fri, Jul 30, 2021 at 12:17:26PM -0700, Eric Biggers wrote:
> > Currently, non-overwrite DIO writes are fundamentally unsafe on f2fs as
> > they require preallocating blocks, but f2fs doesn't support unwritten
> > blocks and therefore has to preallocate the blocks as regular blocks.
> > f2fs has no way to reliably roll back such preallocations, so as a
> > result, f2fs will leak uninitialized blocks to users if a DIO write
> > doesn't fully complete.
There's another way of solving this problem which doesn't require
supporting unwritten blocks. What a file system *could* do is to
allocate the blocks, but *not* update the on-disk data structures ---
so the allocation happens in memory only, so you know that the
physical blocks won't get used for another files, and then issue the
data block writes. On the block I/O completion, trigger a workqueue
function which updates the on-disk metadata to assign physical blocks
to the inode.
That way if you crash before the data I/O has a chance to complete,
the on-disk logical block -> physical block map hasn't been updated
yet, and so you don't need to worry about leaking uninitialized blocks.
Cheers,
- Ted
WARNING: multiple messages have this Message-ID (diff)
From: "Theodore Ts'o" <tytso@mit.edu>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, Jaegeuk Kim <jaegeuk@kernel.org>,
stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes
Date: Fri, 30 Jul 2021 22:46:16 -0400 [thread overview]
Message-ID: <YQS5eBljtztWwOFE@mit.edu> (raw)
In-Reply-To: <YQRQRh1zUHSIzcC/@gmail.com>
On Fri, Jul 30, 2021 at 12:17:26PM -0700, Eric Biggers wrote:
> > Currently, non-overwrite DIO writes are fundamentally unsafe on f2fs as
> > they require preallocating blocks, but f2fs doesn't support unwritten
> > blocks and therefore has to preallocate the blocks as regular blocks.
> > f2fs has no way to reliably roll back such preallocations, so as a
> > result, f2fs will leak uninitialized blocks to users if a DIO write
> > doesn't fully complete.
There's another way of solving this problem which doesn't require
supporting unwritten blocks. What a file system *could* do is to
allocate the blocks, but *not* update the on-disk data structures ---
so the allocation happens in memory only, so you know that the
physical blocks won't get used for another files, and then issue the
data block writes. On the block I/O completion, trigger a workqueue
function which updates the on-disk metadata to assign physical blocks
to the inode.
That way if you crash before the data I/O has a chance to complete,
the on-disk logical block -> physical block map hasn't been updated
yet, and so you don't need to worry about leaking uninitialized blocks.
Cheers,
- Ted
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Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
next prev parent reply other threads:[~2021-07-31 2:46 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-28 1:51 [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes Eric Biggers
2021-07-28 1:51 ` Eric Biggers
2021-07-30 19:17 ` [f2fs-dev] " Eric Biggers
2021-07-30 19:17 ` Eric Biggers
2021-07-30 22:12 ` [f2fs-dev] " Jaegeuk Kim
2021-07-30 22:12 ` Jaegeuk Kim
2021-07-30 22:19 ` Eric Biggers
2021-07-30 22:19 ` [f2fs-dev] " Eric Biggers
2021-07-31 1:05 ` Jaegeuk Kim
2021-07-31 1:05 ` [f2fs-dev] " Jaegeuk Kim
2021-07-31 1:18 ` Eric Biggers
2021-07-31 1:18 ` Eric Biggers
2021-07-31 2:46 ` Theodore Ts'o [this message]
2021-07-31 2:46 ` [f2fs-dev] " Theodore Ts'o
2021-08-02 4:39 ` Eric Biggers
2021-08-02 4:39 ` Eric Biggers
2021-08-02 9:00 ` Chao Yu
2021-08-02 9:00 ` [f2fs-dev] " Chao Yu
2021-08-02 18:23 ` Jaegeuk Kim
2021-08-02 18:23 ` Jaegeuk Kim
2021-08-03 1:19 ` [f2fs-dev] " Chao Yu
2021-08-03 1:19 ` Chao Yu
2021-08-03 1:34 ` [f2fs-dev] " Jaegeuk Kim
2021-08-03 1:34 ` Jaegeuk Kim
2021-08-17 2:03 ` [f2fs-dev] " Eric Biggers
2021-08-17 2:03 ` Eric Biggers
2021-08-17 5:42 ` [f2fs-dev] " Christoph Hellwig
2021-08-17 5:42 ` Christoph Hellwig
2021-08-17 18:57 ` Jaegeuk Kim
2021-08-17 18:57 ` [f2fs-dev] " Jaegeuk Kim
2021-08-17 20:27 ` Eric Biggers
2021-08-17 20:27 ` [f2fs-dev] " Eric Biggers
2021-08-17 21:33 ` Jaegeuk Kim
2021-08-17 21:33 ` Jaegeuk Kim
2021-08-18 0:06 ` [f2fs-dev] " Eric Biggers
2021-08-18 0:06 ` Eric Biggers
2021-08-20 9:35 ` Chao Yu
2021-08-20 9:35 ` [f2fs-dev] " Chao Yu
2021-08-20 18:11 ` Eric Biggers
2021-08-20 18:11 ` Eric Biggers
2021-08-20 22:01 ` [f2fs-dev] " Chao Yu
2021-08-20 22:01 ` Chao Yu
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