linux-kernel - Re: [patch resend v4] update ctime and mtime for mmaped write

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: <20070327123422.d0bbc064.akpm@linux-foundation.org>
Date:	Tue, 27 Mar 2007 12:34:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	linux@...izon.com
Cc:	miklos@...redi.hu, linux-kernel@...r.kernel.org,
	linux-mm@...r.kernel.org
Subject: Re: [patch resend v4] update ctime and mtime for mmaped write

On 27 Mar 2007 15:24:52 -0400
linux@...izon.com wrote:

> > * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
> 
> Yes, I noticed.  See
> http://www.ussg.iu.edu/hypermail/linux/kernel/0602.1/0450.html
> for a bug report on the subject February 2006.

Suggest you use msync(MS_ASYNC), then
sync_file_range(SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE).

The new (post 2.6.17) MAP_SHARED dirty-page semantics mean that the msync()
isn't actually needed.

> That's why this application is still running on 2.4.
> 
> As I mentioned at the time, the SUS says:
> (http://opengroup.org/onlinepubs/007908799/xsh/msync.html)
> "When MS_ASYNC is specified, msync() returns immediately once all the
> write operations are initiated or queued for servicing."
> 
> You can argue that putting it on the dirty list constitutes "queued for
> servicing", but the intent seems pretty clear to me: MS_ASYNC is supposed
> to start the I/O.  Although strict standards-ese parsing says that
> either branch of an or is acceptable, it is a common English language
> convention that the first alternative is preferred and the second
> is a fallback.
> 
> It makes sense in this case: start the write or, if that's not possible
> (the disk is already busy), queue it for service as soon as the disk
> is available.
> 
> They perhaps didn't mandate it this strictly, but that's clearly the
> intent.

We can fix your application, and we'll break someone else's.

I don't think it's solveable, really - the range of applications is so
broad, and the "standard" is so vague as to be useless.  This is why we've
been extending these things with linux-specific goodies which permit
applications to actually tell the kernel what they want to be done in a
more finely-grained fashion.
-
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/