linux-kernel - Re: [PATCH 1/6] fs: add hole punching to fallocate

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: <20101109214147.GK3099@thunk.org>
Date:	Tue, 9 Nov 2010 16:41:47 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Dave Chinner <david@...morbit.com>
Cc:	Josef Bacik <josef@...hat.com>, linux-kernel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, xfs@....sgi.com,
	joel.becker@...cle.com, cmm@...ibm.com, cluster-devel@...hat.com
Subject: Re: [PATCH 1/6] fs: add hole punching to fallocate

On Tue, Nov 09, 2010 at 03:42:42PM +1100, Dave Chinner wrote:
> Implementation is up to the filesystem. However, XFS does (b)
> because:
> 
> 	1) it was extremely simple to implement (one of the
> 	   advantages of having an exceedingly complex allocation
> 	   interface to begin with :P)
> 	2) conversion is atomic, fast and reliable
> 	3) it is independent of the underlying storage; and
> 	4) reads of unwritten extents operate at memory speed,
> 	   not disk speed.

Yeah, I was thinking that using a device-style TRIM might be better
since future attempts to write to it won't require a separate seek to
modify the extent tree.  But yeah, there are a bunch of advantages of
simply mutating the extent tree.

While we're on the subject of changes to fallocate, what do people
think of FALLOC_FL_EXPOSE_OLD_DATA, which requires either root
privileges or (if capabilities are in use) CAP_DAC_OVERRIDE &&
CAP_MAC_OVERRIDE && CAP_SYS_ADMIN.  This would allow a trusted process
to fallocate blocks with the extent already marked initialized.  I've
had two requests for such functionality for ext4 already.  

(Take for example a trusted cluster filesystem backend that checks the
object checksum before returning any data to the user; and if the
check fails the cluster file system will try to use some other replica
stored on some other server.)

    		     	  		    	 - Ted
--
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/