[RFC][PATCH 7/8]: Auto-create ptmx node when mounting devpts

H. Peter Anvin hpa at zytor.com
Thu Aug 21 09:09:19 PDT 2008

Alan Cox wrote:
>> This patch has the kernel internally create the [ptmx, c, 5:2] device
>> when mounting devpts filesystem. The permissions for the device node
>> can be specified by the '-o ptmx_mode=0666' option. The default mode
>> is 0666.
>> 	Hopefully, presence of the 'ptmx' node in /dev/pts does not surprise
>> 	user space.
> If you are going to make major changes requiring user space changes to
> use them then you can change the user space rather than playing "gee
> where did that come from" with the existing system.

This particular one I think is the right thing, despite everything.  In 
particular, it makes a *hell* of a lot more sense to have this 
auto-created, than supporting mknod(2) inside the devpts filesystem. 
It's not a matter of "changing the user space"; it's a matter of what 
makes most sense inside the kernel.

His new implementation doesn't require user space changes unless you 
want to take advantages of the multi-instance features.  It thus allows 
for a soft transition.  However, soft or hard transition is irrelevant 
-- creating ptmx inside devpts is necessary, and it doesn't make sense 
to require userspace to mknod it, since the kernel code ends up being 
more complex.


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