linux-kernel - Re: [PATCH] fanotify: add a flag to allow setting O

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Message-ID: <CAKgNAkjEMEfgQurTFS5bUyC4U2WkuYBG72ARjNkn=W=OWPSEaw@mail.gmail.com>
Date:	Thu, 2 Oct 2014 13:55:53 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Pádraig Brady <P@...igbrady.com>
Cc:	Yann Droneaud <ydroneaud@...eya.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Heinrich Schuchardt <xypron.glpk@....de>,
	Eric Paris <eparis@...hat.com>,
	Richard Guy Briggs <rgb@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	stable@...r.kernel.org, Linux API <linux-api@...r.kernel.org>,
	Jan Kara <jack@...e.cz>,
	Lino Sanfilippo <LinoSanfilippo@....de>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>
Subject: Re: [PATCH] fanotify: add a flag to allow setting O_CLOEXEC on event fd

On Thu, Oct 2, 2014 at 11:13 AM, Pádraig Brady <P@...igbrady.com> wrote:
> On 10/02/2014 08:52 AM, Yann Droneaud wrote:
>> In order to not potentially break applications which were
>> requesting O_CLOEXEC on event file descriptors but which
>> actually need it to be not effective as the kernel currently
>> ignore the flag, so the file descriptor is inherited accross
>> exec regardless of O_CLOEXEC (please forgive me for the
>> wording), this patch introduces FAN_FD_CLOEXEC flag to
>> fanotify_init() so that application can request O_CLOEXEC
>> to be effective.
>> Newer application would use FAN_FD_CLOEXEC flag along
>> O_CLOEXEC to enable close on exec on newly created
>> file descriptor:
>>
>>   fd = fanotify_init(FAN_CLOEXEC|FAN_NONBLOCK|FAN_FD_CLOEXEC,
>>                      O_RDONLY|O_LARGEFILE|O_CLOEXEC|O_NOATIME);
>
> Ugh really?
> IMHO there should be widespread or at least known breakage with
> O_CLOEXEC before adding messiness like this.
> It seems surprising to me that apps that would depend on
> O_CLOEXEC being ineffective.
>
> please reconsider this one.

Agreed. The number of applications for which there are silent (not
*yet* observed) breakages because O_CLOEXEC is not working as expected
is likely rather larger than the set of applications that randomly
specify O_CLOEXEC and then somehow get broken as a result.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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