linux-kernel - Re: Question about REQ_FLUSH and bios with data

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: <1376079495.2718.15.camel@menhir>
Date:	Fri, 09 Aug 2013 21:18:15 +0100
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	scameron@...rdog.cce.hp.com
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...nel.dk, tj@...nel.org
Subject: Re: Question about REQ_FLUSH and bios with data

Hi,

On Fri, 2013-08-09 at 14:09 -0500, scameron@...rdog.cce.hp.com wrote:
> So, I'm working on a block driver using the make_request_fn
> interface, and have to handle a bio that comes in with
> (bi_rw & REQ_FLUSH) set AND data to transfer. 
> 
> According to Documentation/block/writeback_cache_control.txt:
> 
> 	The REQ_FLUSH flag can be OR ed into the r/w flags of a
> 	bio submitted from the filesystem and will make sure the
> 	volatile cache of the storage device has been flushed
> 	before the actual I/O operation is started. 
> 
> So I've written code that handles that case, along with the
> various error cases I might encounter, I think, which leads
> to my question:
> 
> How do I get such a bio with a data transfer AND the REQ_FLUSH bit
> set to come into the driver?   Just wondering how to test this case.
> 
GFS2 does this... if you look at the log flush code and the function
log_write_header() in particular, you'll see that it sets this on each
log header that gets written. You don't need a cluster to generate this
kind of i/o, just supply mkfs.gfs2 with -p lock_nolock and mount it as a
local filesystem. The combination of touch foo; sync should be enough to
generate a log flush writing a log header with this flag set,

Steve.

> Thanks,
> 
> (I cc'ed Tejun Heo just because his name is in block/blk-flush.c)
> 
> -- steve
> 
> --
> 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/


--
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/