Re: [PATCH 2/2] tty: rework pty count limiting

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Greg KH wrote:
> On Mon, Jan 02, 2012 at 09:23:01PM +0400, Konstantin Khlebnikov wrote:
>> After adding devpts multiple-insrances sysctl kernel.pty.max limit pty count for
>> each devpts instance independently, while kernel.pty.nr shows total pty count.
>>
>> This patch restores sysctl kernel.pty.max as global limit (4096 by default),
>> adds pty reseve for main devpts (mounted without "newinstance" argument),
>> and new sysctl to tune it: kernel.pty.reserve (1024 by default)
>>
>> Also it adds devpts mount option "max=%d" to limit pty count for each devpts
>> instance independently. (by default NR_UNIX98_PTY_MAX == 2^20)
>>
>> Thus devpts instances in containers cannot eat up all available pty even if we didn't
>> set any limits, while with "max" argument we can adjust limits more precisely.
>>
>> Plus, now open("/dev/ptmx") return -ENOSPC in case lack of pty indexes,
>> this is more informative than -EIO.
>
> That's a userspace api change, why is this going to be allowed?

open() can return -ENOSPC in case normal fs,
meanwhile error codes for /dev/ptmx wasn't documented at all:
there is nothing in manpage pts, pty and ptmx.
manpage posix_openpt and getpt refers to manpage open(2).
I can return EIO back, if this is critical.

>
> greg k-h