Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance

[H. Peter Anvin]

On 12/11/15 14:12, Andy Lutomirski wrote:
>>
>> For the newinstance case st_dev should match between the master and the
>> slave.  Unfortunately this is not the case for a legacy ptmx, as a
>> stat() on the master descriptor still returns the st_dev, st_rdev, and
>> st_ino for the ptmx device node.
> 
> Sure, but I'm not talking about stat.  I'm saying that we could add a
> new ioctl that works on any ptmx fd (/dev/ptmx or /dev/pts/ptmx) that
> answers the question "does this ptmx logically belong to the given
> devpts filesystem".
> 
> Since it's not stat, we can make it do whatever we want, including
> following a link to the devpts instance that isn't f_path or f_inode.
> 

Sure.  My thinking, though, was whether or not we can do something that
works on legacy kernels, and/or is less intrusive than new ioctls.

What is the actual operation we need?

	-hpa

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