linux-kernel - Re: [PATCH v2 1/2] coredump: use task comm instead of (unknown)

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Date:	Tue, 07 Jun 2011 20:30:11 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Jiri Slaby <jslaby@...e.cz>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v2 1/2] coredump: use task comm instead of (unknown)

On 06/07/2011 08:16 PM, Oleg Nesterov wrote:
> On 06/07, Jiri Slaby wrote:
>>
>> @@ -1631,7 +1631,7 @@ static int cn_print_exe_file(struct core_name *cn)
>>
>>  	exe_file = get_mm_exe_file(current->mm);
>>  	if (!exe_file)
>> -		return cn_printf(cn, "(unknown)");
>> +		return cn_printf(cn, "%s (path unknown)", current->comm);
> 
> Hmm. The patch itself looks fine to me.
> 
> Acked-by: Oleg Nesterov <oleg@...hat.com>
> 
> 
> 
> But the code looks wrong.
> 
> What if d_path() fails with, say, ENAMETOOLONG? do_coredump() doesn't
> expect an error code != ENOMEM. This is just ugly, I'll send the simple
> fix. Anyway, if we are changing cn_print_exe_file(), perhaps it makes
> sense to fallback if d_path fails too?

Ah, I see. Perhaps it should check '< 0' instead of '== -ENOMEM' and
print the error in that case?

> And, I am just noticed...
> 
> 	for (p = path; *p; p++)
> 		if (*p == '/')
> 			*p = '!';
> 
> Why??? I am not arguing, just curious.

In fact the reason is in the patch 2/2:
    coredump: escape / in hostname and comm

    Change every occurence of / in comm and hostname to !. If the process
    changes its name to contain /, the core is not dumped (if the
    directory tree doesn't exist like that). The same with hostname being
    something like myhost/3. Fix this behaviour by using the escape loop
    used in %E. (We extract it to a separate function.)

    Now both with comm == myprocess/1 and hostname == myhost/1, the core
    is dumped like (kernel.core_pattern='core.%p.%e.%h):
    core.2349.myprocess!1.myhost!1

thanks,
-- 
js
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