linux-ext4 - Re: Problems with determining data presence by examining extents?

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: <24480.1579097734@warthog.procyon.org.uk>
Date:   Wed, 15 Jan 2020 14:15:34 +0000
From:   David Howells <dhowells@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
        viro@...iv.linux.org.uk, tytso@....edu, adilger.kernel@...ger.ca,
        darrick.wong@...cle.com, clm@...com, josef@...icpanda.com,
        dsterba@...e.com, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Problems with determining data presence by examining extents?

Christoph Hellwig <hch@....de> wrote:

> The whole idea of an out of band interface is going to be racy and suffer
> from implementation loss.  I think what you want is something similar to
> the NFSv4.2 READ_PLUS operation - give me that if there is any and
> otherwise tell me that there is a hole.  I think this could be a new
> RWF_NOHOLE or similar flag, just how to return the hole size would be
> a little awkward.  Maybe return a specific negative error code (ENODATA?)
> and advance the iov anyway.

Just having call_iter_read() return a short read could be made to suffice...
provided the filesystem doesn't return data I haven't written in (which could
cause apparent corruption) and does return data I have written in (otherwise I
have to go back to the server).

David