Messages in this thread | | | Date | Sat, 07 Apr 2012 15:03:24 -0700 | From | "H. Peter Anvin" <> | Subject | Re: RFC: deprecating/removing the legacy mode of devpts |
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On 04/07/2012 02:27 PM, Ted Ts'o wrote: > On Sat, Apr 07, 2012 at 01:02:33PM -0700, H. Peter Anvin wrote: >> The problem is that the lack of migration at the root causes real >> problems for the people who need the extra funkiness, and unlike BSD >> ttys it's not an application-level change at all. > > Could you explain what the issues are? I haven't been following > devpts all that carefully. >
The issue is that to make the "ptys are private to an instance of the devpts filesystem", /dev/ptmx has to live inside the /dev/pts filesystem. This was traditionally not the case. To avoid breaking everything all at once, we have a legacy mode which supports the "all devpts instances are the same" (effectively bind mounts) and which support a /dev/ptmx outside /dev/pts.
The problem is that anyone who wants to take advantage of the new functionality has to make sure *all* instances of devpts work with the new protocol. This means modifying your distro to:
1. Add "newinstance" and "ptmxmode" to /etc/fstab [easy] 2. Make /dev/ptmx a symlink to /dev/pts/ptmx.
2 would be easy if it wasn't for udev, which makes it very hard. It is not reasonable for udev to support both modes, so the *only* mode that is reasonable for it to support is the new mode. However, it is increasingly obvious that if we don't force it, this will never happen.
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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