On 03/24/2017 03:53 PM, Christian Brauner wrote:
> Sorry, for the late reply.
>
> On Fri, Mar 24, 2017 at 3:40 PM, Michael Kerrisk (man-pages)
> <mtk.manpages@xxxxxxxxx> wrote:
>> Hi Dmitry,
>>
>> On 03/20/2017 10:58 PM, Dmitry V. Levin wrote:
>>> Hi,
>>>
>>> On Mon, Mar 20, 2017 at 10:02:15PM +0100, Christian Brauner wrote:
>>>> Hi,
>>>>
>>>> Thanks Dmitry. One comment
>>>>
>>>> On 20 Mar 2017 9:51 p.m., "Dmitry V. Levin" <ldv@xxxxxxxxxxxx> wrote:
>>>>
>>>> ---
>>>> man3/ttyname.3 | 8 +++++++-
>>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/man3/ttyname.3 b/man3/ttyname.3
>>>> index 14c24e7..0be50c6 100644
>>>> --- a/man3/ttyname.3
>>>> +++ b/man3/ttyname.3
>>>> @@ -71,6 +71,11 @@ File descriptor does not refer to a terminal device.
>>>> .RB ( ttyname_r ())
>>>> .I buflen
>>>> was too small to allow storing the pathname.
>>>> +.TP
>>>> +.\" glibc commit 15e9a4f378c8607c2ae1aa465436af4321db0e23
>>>> +.B ENODEV
>>>> +File descriptor refers to a slave pseudoterminal device
>>>> +but the corresponding pathname could not be found.
>>>>
>>>> I think it would be good to explicitly mention that ENODEV is set in case
>>>> the fd does not refer to a pts device in its namespace. Otherwise users
>>>> might take this as an indication that this is a more generic error which is
>>>> not the case.
>>>
>>> In fact, this is a more generic error than a namespace mismatch, although
>>> the latter is the most likely reason.
>>>
>>> Imagine that the corresponding file inside /dev/pts/ is not available for
>>> some reason and the stat call has failed. This situation could be
>>> reproduced e.g. by bind-mounting an empty directory to /dev/pts.
>>> A subsequent ttyname invocation would end up with ENODEV because the device
>>> is literally not available although it's withing the same namespace.
>>>
>>> I don't mind if you change the description to mention the namespace case
>>> as the most likely, but please do not make it the only case when ENODEV
>>> can happen.
>>
>> I'm open on this point. If someone wants to write a suitable patch, I'll
>> probably take it.
>
> This point is in my opinion crucial. The over-mounting scenario is
> still a valid case for most programs that do not actually care about
> what /dev/pts/<n> is actually used to go on which is a nice side-effect
> of the patch. The namespace part should be mentioned since ttyname{_r}()
> explicitly does not return anything when it detects that
> /proc/self/fd/<n> points to /dev/pts/<n> but /dev/pts/<n> does not exist
> in the same namespace. This was the original motivation when we
> wrote the patch. So users that get ENODEV from ttyname{_r}() should
> be aware that resolving the symlink manually afterwards doesn't give them
> a /dev/pts/<n> path valid in the current namespace.
>
> I'll put this on my TODO list but if someone is willing to send a
> patch right away
> please do so. :)
Hi Christian,
I think you may be best placed to know what you want to convey here.
I'd be happy to receive a patch.
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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