linux-kernel - Re: [RFC PATCH 1/2] fs: introduce FALLOC_FL_FORCE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <f26a21c9-2520-4deb-98f5-385adc92a934@huaweicloud.com>
Date: Wed, 8 Jan 2025 09:20:30 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: "Darrick J. Wong" <djwong@...nel.org>, Theodore Ts'o <tytso@....edu>,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk, brauner@...nel.org,
 jack@...e.cz, adilger.kernel@...ger.ca, yi.zhang@...wei.com,
 chengzhihao1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com,
 Sai Chaitanya Mitta <mittachaitu@...il.com>, linux-xfs@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] fs: introduce FALLOC_FL_FORCE_ZERO to fallocate

On 2025/1/8 0:42, Christoph Hellwig wrote:
> On Tue, Jan 07, 2025 at 10:05:47PM +0800, Zhang Yi wrote:
>> Sorry. the "pure overwrites" and "always-cow files" makes me confused,
>> this is mainly used to create a new written file range, but also could
>> be used to zero out an existing range, why you mentioned it exists to
>> facilitate pure overwrites?
> 
> If you're fine with writes to your file causing block allocations you
> can already use the hole punch or preallocate fallocate modes.  No
> need to actually send a command to the device.
> 

Okay, I misunderstood your point earlier. This is indeed prepared for
subsequent overwrites. Thanks a lot for explaining.

Thanks,
Yi.

>>
>> For the "always-cow files", do you mean reflinked files? Could you
>> please give more details?
> 
> reflinked files will require out of place writes for shared blocks.
> As will anything on device mapper snapshots.  Or any file on
> file systems that write out of place (btrfs, f2fs, nilfs2, the
> upcoming zoned xfs mode).
>