linux-kernel - Re: [PATCH v5 04/11] blksnap: header file of the module interface

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

Message-ID: <c4c9da4f-0d82-4e35-0365-f246666f0c37@veeam.com>
Date:   Wed, 14 Jun 2023 18:43:10 +0200
From:   Sergei Shtepa <sergei.shtepa@...am.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Dave Chinner <david@...morbit.com>, <axboe@...nel.dk>,
        <corbet@....net>, <snitzer@...nel.org>, <viro@...iv.linux.org.uk>,
        <brauner@...nel.org>, <dchinner@...hat.com>, <willy@...radead.org>,
        <dlemoal@...nel.org>, <linux@...ssschuh.net>, <jack@...e.cz>,
        <ming.lei@...hat.com>, <linux-block@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>,
        "Donald Buczek" <buczek@...gen.mpg.de>
Subject: Re: [PATCH v5 04/11] blksnap: header file of the module interface



On 6/14/23 16:07, Christoph Hellwig wrote:
> I don't actually think swapfile is a very good idea, in fact the Linux
> swap code in general is not a very good place to look for inspirations
> 😄

Perhaps. I haven't looked at the code yet. But I like the idea of
protecting the file from any access from the user-space, as it is
implemented for swapfile.

> 
> IFF the usage is always to have a whole file for the diff storage the
> over all API is very simple - just pass a fd to the kernel for the area,
> and then use in-kernel direct I/O on it.  Now if that file should also
> be able to reside on the same file system that the snapshot is taken
> of things get a little more complicated, because writes to it also need
> to automatically set the BIO_REFFED flag.

There is definitely no task to create a difference storage file on the
same block device for which the snapshot is being created. The file can
be created on any block device.

Still, the variant when a whole partition is allocated for the difference
storage can also be useful.

> I have some ideas for that and will share some draft code with you.

I'll be glad.