Re: [Xen-devel] [PATCH XEN v6 29/32] tools/libs/call: Use O_CLOEXEC when opening /dev/xen/privcmd on Linux

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 11/12/15 a les 18.22, Ian Campbell ha escrit:
> On Wed, 2015-12-09 at 16:17 +0000, Ian Jackson wrote:
>> Ian Campbell writes ("[PATCH XEN v6 29/32] tools/libs/call: Use O_CLOEXEC
>> when opening /dev/xen/privcmd on Linux"):
>>> We stick with using FD_CLOEXEC on the legacy /proc/xen/privcmd
>>> fallback device since it was present in older kernel where O_CLOEXEC
>>> may not be assured.
>>
>> This is a lot of effort and may not be needed.  I don't object, but
>> some of the statements are (I think) rather too fierce:
>>
>>> +    /*
>>> +     * This file descriptor is opaque to the caller, thus we must take
>>> +     * responsibility to ensure it doesn't propagate (ie leak) outside
>>> +     * the process, by using CLOEXEC.
>>> +     */
>>
>> For example, I don't think this is a `must' at all, although not
>> propagating irrelevant fds is (nowadays) seen as polite.
> 
> Right, this bit was actually (mostly) code^Wcomment motion.
> 
> I'll happily update it to say polite rather than required.
> 
> I did a bit more investigation of O_CLOEXEC and found that Linux introduced
> it in 2.6.23 (October 2007) which seems to be old enough that we should
> just use it anywhere we feel it necessary.
> 
> Jan did mention (on IRC) that while he doesn't use any kernels so old, he
> still occasionally builds on userspace which is old enough to lack the
> definition, hence I would do #ifndef+#define.
> 
> Roger, I see that open(2) on FreeBSD mentions O_CLOEXEC too. Do you know
> when that arrived and whether it is something we can assume these days?
> I found a posting of the patch in https://lists.freebsd.org/pipermail/freeb
> sd-fs/2011-March/011021.html, but I don't know when it landed or when it
> became something code could assume.

privcmd is only available on FreeBSD HEAD anyway, and AFAICT (by looking
at the man pages) all stable FreeBSD versions support O_CLOEXEC (10.2,
9.3 and 8.4).

I think we can safely assume O_CLOEXEC is available in all FreeBSD
version we build on.

Roger.


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