linux-kernel - Re: [PATCHSET] printk: implement printk

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: <1200951757.3860.24.camel@cinder.waste.org>
Date:	Mon, 21 Jan 2008 15:42:37 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	linux-kernel@...r.kernel.org, daniel.ritz-ml@...ssonline.ch,
	randy.dunlap@...cle.com, jeff@...zik.org,
	linux-ide@...r.kernel.org, Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCHSET] printk: implement printk_header() and merging printk


On Sat, 2008-01-19 at 07:58 +0900, Tejun Heo wrote:
> Matt Mackall wrote:
> > On Wed, 2008-01-16 at 10:00 +0900, Tejun Heo wrote:
> >> And mprintk the following.
> >>
> >>  code:
> >>   DEFINE_MPRINTK(mp, 2 * 80);
> >>
> >>   mprintk_set_header(&mp, KERN_INFO "ata%u.%2u: ", 1, 0);
> >>   mprintk_push(&mp, "ATA %d", 7);
> >>   mprintk_push(&mp, ", %u sectors\n", 1024);
> >>   mprintk(&mp, "everything seems dandy\n");
> > 
> > I prefer Matthew Wilcox's stringbuf approach which does proper memory
> > management and isn't specific to printk:
> > 
> > http://www.ussg.iu.edu/hypermail/linux/kernel/0710.3/0517.html
> 
> Yeap, that's generic and nice but I think both 'generic' and 'proper
> memory management' are weakness if what you're trying to do is to
> support collecting messages in pieces and putting it out via printk.
> Please consider the following scenario.
> 
> You're in an interrupt handler and detected a severe error condition
> which should be notified to the user but the information is rather
> complex and best built in pieces, so you create a stringbuf and does
> sb_printf() to it w/ GFP_ATOMIC but alas memory allocation failed and
> you end up printing "out of memory" unless you detect the failure and go
> back and printk messages piece-by-piece manually.  I would rather
> assemble the message manually from the get-go into an on-stack buffer.

I suppose. I still find this approach less than ideal, especially
putting something potentially large on the stack. The dangers are
perhaps worse than a malloc, really. 

I also don't like your interface much. Consider this alternative:

struct mprintk *mp = mprintk_begin(KERN_INFO "ata%u.%2u: ", 1, 0);
mprintk(mp, "ATA %d", 7);
mprintk(mp, ", %u sectors\n", 1024);
mprintk(mp, "everything seems dandy\n");
mprintk_end(mp);

That keeps all the "normal" printks short and makes the flush more
explict.

Now we make mprintk_begin attempt to do a kmalloc of a moderate size
(512 bytes?) and failing that, return null. Then mprintk can fall
through to printk in the NULL case.

-- 
Mathematics is the supreme nostalgia of our time.

--
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/