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From: Christoph Hellwig <hch@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>,
	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 08:16:03 +0100	[thread overview]
Message-ID: <20200827071603.GA25305@infradead.org> (raw)
In-Reply-To: <20200825145056.GC32298@quack2.suse.cz>

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.

  reply	other threads:[~2020-08-27  7:16 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 [this message]
2020-08-27 21:39         ` Al Viro
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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