linux-kernel - Re: [RFC] error management in add

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Message-ID: <20070724132805.GR21668@ftp.linux.org.uk>
Date:	Tue, 24 Jul 2007 14:28:05 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Alban Crequy <alban.crequy@...nodes.com>
Cc:	jens.axboe@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC] error management in add_disk()

On Tue, Jul 24, 2007 at 01:57:53PM +0200, Alban Crequy wrote:
> Hi,
> 
> I have a problem with the error management of add_disk() and del_gendisk().
> 
> add_disk() adds an entry in /sys/block/<name>. The filename in /sys/block is
> not (struct gen_disk)->disk_name but more or less the first KOBJ_NAME_LEN
> characters of (struct gen_disk)->disk_name.
> 
> #define KOBJ_NAME_LEN                   20
> 
> My problem occurs when we try to add 2 disks with different names, but when
> the KOBJ_NAME_LEN first characters are the same.

So don't do that.

> The attached test module triggers the problem. You can try something like:
> for i in $(seq 1 100) ; do insmod ./adddiskbug.ko ; rmmod adddiskbug ; done
> 
> The attached patch fixes the problem by changing the prototype of add_disk() and
> register_disk() to return errors.

This is bogus.  Just what would callers do with these error values?
Ignore them silently?  Bail out?  Can't do - at that point disk just might
have been opened already.  add_disk() is the point of no return; we are
already past the last point where we could bail out.
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