linux-kernel - Re: Zero length files - an alternative approach?

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: <49CFA684.2040102@redhat.com>
Date:	Sun, 29 Mar 2009 19:49:08 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Graham Murray <graham@...rray.org.uk>
CC:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Zero length files - an alternative approach?

Graham Murray wrote:
> Just a thought on the ongoing discussion of dataloss with ext4 vs ext3.
>
> Taking the common scenario:
> Read oldfile
> create newfile file
> write newfile data
> close newfile
> rename newfile to oldfile
>
> When using this scenario, the application writer wants to ensure that
> either the old or new content are present. With delayed allocation, this
> can lead to zero length files. Most of the suggestions on how to address
> this have involved syncing the data either before the rename or making
> the rename sync the data.
>
> What about, instead of 'bringing forward' the allocation and flushing of
> the data, would it be possible to instead delay the rename until after
> the blocks for newfile have been allocated and the data buffers flushed?
> This would keep the performance benefits of delayed allocation etc and
> also satisfy the applications developers' apparent dislike of using
> fsync(). It would give better performance that syncing the data at
> rename time (either using fsync() or automatically) and satisfy the
> requirements that either the old or new content is present.
>
> I am not a filesystem developer, so do not know how feasible this would
> be. 
>   

This has been suggested, I believe.  In filesystem terms, it means 
inserting a barrier before the rename operation, meaning that any write 
operations needed to carry out the rename must not take place until all 
write operations from the previous calls have completed.


-- 
error compiling committee.c: too many arguments to function

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/