Increasing ptys/ttys beyond 128

[Eric Brunson]

I have a patch for expect, what's the process for getting it reviewed 
for incorporation into ports?

Eric Brunson wrote:
> Erik Trulsson wrote:
>> On Wed, Dec 13, 2006 at 10:42:46AM -0700, Eric Brunson wrote:
>>  
>>> I've done some searching on the web, but everything I've come across 
>>> is either out of date and says to recompile the kernel, or else says 
>>> that after 5.1 the devfs does it automatically.  I don't think 
>>> that's the case.
>>>
>>> I'm running 6.1 and I need more than the [pt]ty[p-sP-S] devices that 
>>> will auto-clone in devfs.
>>>
>>> I've tried adding lines like the following to /etc/default/devfs.rules:
>>>
>>> add path 'ptyt*' unhide
>>> add path 'ttyt*' unhide
>>>
>>> But that doesn't do the trick.  The syntax "unhide" implies to me 
>>> that the [p-sP-S] nodes exist but but are hidden by the hide_all 
>>> ruleset.
>>>
>>> What do I have to do to allow the creation of more ptys?
>>>     
>>
>> I don't think you can have more than 256 pty devices in 6.1
>>
>> The code in the kernel that handles ptys only allow for 
>> pty[pqrsPQRS][0-9a-v]
>> (and the corresponding tty[pqrsPQRS][0-9a-v] of course.)  This gives 
>> you a
>> total of 8*32 = 256 pty devices. (Not 128 as the subjectline implies.)
>>   
>
> Actually, that is incredibly helpful.  We're having problems with 
> expect, but when expect searches for a free pty, it only searches 
> [0-9a-f], which only gives us 128 ptys.  There's another problem with 
> this search resulting in failures after 64 pty allocations which I was 
> trying to avoid patching in expect, but if I can get 256 processes out 
> of it, I'll patch away.
>
> Man, 5 days of searching the web and you set me straight in 48 
> minutes... I should have started here first.  :-)
>
> Thanks a *ton*!
>
>> (I don't think you could have more than 256 ptys back in 4.x either, but
>>  back then the default setup only gave you 32 ptys, and all the 
>> instructions  I have seen for increasing that number only told how to 
>> let you use all 256
>>  possible devices, but not more than that.)
>>
>>
>> To get more ptys than 256 you will have to start hacking the kernel.  
>> (There
>> does seem to be an alternate naming system for ptys available in 
>> 7-CURRENT
>> but it has not been back-ported to 6.x.  See the pty(4) manpage from
>> -CURRENT for details on how it works.
>
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