From: Al Viro <viro@zeniv.linux.org.uk>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org, yebin <yebin10@huawei.com>,
linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH RFC 2/2] block: Do not discard buffers under a mounted filesystem
Date: Thu, 27 Aug 2020 22:39:00 +0100 [thread overview]
Message-ID: <20200827213900.GG1236603@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200827071603.GA25305@infradead.org>
On Thu, Aug 27, 2020 at 08:16:03AM +0100, Christoph Hellwig wrote:
> On Tue, Aug 25, 2020 at 04:50:56PM +0200, Jan Kara wrote:
> > Do you mean that address_space filesystem uses to access its metadata on
> > /dev/sda will be different from the address_space you will see when reading
> > say /dev/sda? Thus these will be completely separate (and incoherent)
> > caches?
>
> Yes.
>
> > Although this would be simple it will break userspace I'm afraid.
> > There are situations where tools read e.g. superblock of a mounted
> > filesystem from the block device and rely on the data to be reasonably
> > recent. Even worse e.g. tune2fs or e2fsck can *modify* superblock of a
> > mounted filesystem through the block device (e.g. to set 'fsck after X
> > mounts' fields and similar).
>
> We've not had any problems when XFS stopped using the block device
> address space 9.5 years ago.
How much writes from fsck use does xfs see, again?
next prev parent reply other threads:[~2020-08-27 21:39 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-25 12:05 [PATCH RFC 0/2] Block and buffer invalidation under a filesystem Jan Kara
2020-08-25 12:05 ` [PATCH RFC 1/2] fs: Don't invalidate page buffers in block_write_full_page() Jan Kara
2020-08-25 12:05 ` [PATCH RFC 2/2] block: Do not discard buffers under a mounted filesystem Jan Kara
2020-08-25 12:16 ` Christoph Hellwig
2020-08-25 14:10 ` Theodore Y. Ts'o
2020-08-25 15:12 ` Jan Kara
2020-08-25 18:41 ` Matthew Wilcox
2020-08-25 18:49 ` Jan Kara
2020-08-25 14:50 ` Jan Kara
2020-08-27 7:16 ` Christoph Hellwig
2020-08-27 21:39 ` Al Viro [this message]
2020-08-28 0:07 ` Dave Chinner
2020-08-28 8:10 ` Jan Kara
2020-08-28 8:21 ` Andreas Dilger
2020-08-29 6:40 ` Christoph Hellwig
2020-08-31 7:48 ` Jan Kara
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