From: Christoph Hellwig <hch@lst.de>
To: David Howells <dhowells@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
Qu Wenruo <quwenruo.btrfs@gmx.com>,
Andreas Dilger <adilger@dilger.ca>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
David Sterba <dsterba@suse.com>,
linux-ext4 <linux-ext4@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Problems with determining data presence by examining extents?
Date: Thu, 16 Jan 2020 11:13:44 +0100 [thread overview]
Message-ID: <20200116101344.GA16435@lst.de> (raw)
In-Reply-To: <28755.1579100378@warthog.procyon.org.uk>
On Wed, Jan 15, 2020 at 02:59:38PM +0000, David Howells wrote:
> Another thread could be writing to the file at the same time, but not in the
> same block. That's managed by netfs, most likely based on the pages and page
> flags attached to the netfs inode being cached in this particular file[*].
>
> What I was more thinking of is that SEEK_HOLE might run past the block of
> interest and into a block that's currently being written and see a partially
> written block.
But that's not a problem given that you know where to search.
>
> [*] For AFS, this is only true of regular files; dirs and symlinks are cached
> as monoliths and are there entirely or not at all.
>
> > > However, SEEK_HOLE doesn't help with the issue of the filesystem 'altering'
> > > the content of the file by adding or removing blocks of zeros.
> >
> > As does any other method. If you need that fine grained control you
> > need to track the information yourself.
>
> So, basically, I can't. Okay. I was hoping it might be possible to add an
> ioctl or something to tell filesystems not to do that with particular files.
File systems usually pad zeroes where they have to, typically for
sub-blocksize writes. Disabling this would break data integrity.
next prev parent reply other threads:[~2020-01-16 10:13 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 16:48 Problems with determining data presence by examining extents? David Howells
2020-01-14 22:49 ` Theodore Y. Ts'o
2020-01-15 3:54 ` Qu Wenruo
2020-01-15 12:46 ` Andreas Dilger
2020-01-15 13:10 ` Qu Wenruo
2020-01-15 13:31 ` Christoph Hellwig
2020-01-15 19:48 ` Andreas Dilger
2020-01-16 10:16 ` Christoph Hellwig
2020-01-15 20:55 ` David Howells
2020-01-15 22:11 ` Andreas Dilger
2020-01-15 23:09 ` David Howells
2020-01-26 18:19 ` Zygo Blaxell
2020-01-15 14:35 ` David Howells
2020-01-15 14:48 ` Christoph Hellwig
2020-01-15 14:59 ` David Howells
2020-01-16 10:13 ` Christoph Hellwig [this message]
2020-01-17 16:43 ` David Howells
2020-01-15 14:20 ` David Howells
2020-01-15 8:38 ` Christoph Hellwig
2020-01-15 13:50 ` David Howells
2020-01-15 14:05 ` David Howells
2020-01-15 14:24 ` Qu Wenruo
2020-01-15 14:50 ` David Howells
2020-01-15 14:15 ` David Howells
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