Re: [PATCH] ttyname.3: document ENODEV error code

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Christian,

Pink on the below!

Cheers,

Michael


On 03/26/2017 02:47 PM, Michael Kerrisk (man-pages) wrote:
> 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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 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-u2l5PoMzF/Vg9hUCZPvPmw@public.gmane.org> 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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