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    SubjectRe: Per-instance devpts
    H. Peter Anvin [hpa@zytor.com] wrote:
    > Since the issue of PTY namespaces came up (and was rejected) back in April,
    > I have thought a little bit about changing ptys to be tied directly into a
    > devpts instance. devpts would then be a "normal" filesystem, which can be
    > mounted multiple times (or not at all). pty's would then become private to
    > a devpts instance.

    Sorry, I thought we were going with a complete device namespace - since that
    would address other devices as well and would avoid the following user-space
    issue.

    I guess this issue came up in OLS recently and have been looking into this
    again. I have some helper patches to explore multiple mounts of devpts
    without namespace stuff and can send them out in a couple of days.

    >
    > This is what it would appear would have to change, and I'd like to get
    > people's feeing for the user-space impact:
    >
    > 1. /dev/ptmx would have to change to a symlink, ptmx -> pts/ptmx.

    IIRC, /dev/tty also needs a similar symlink.

    > 2. Permissions on /dev/ptmx would not be persistent, and would have to
    > be set via devpts mount options (unless they're 0666 root.tty, which
    > would presumably be the default.)
    > 3. The /proc/sys/kernel/pty limit would be global; a per-filesystem
    > limit could be added on top or instead (presumably via a filesystem
    > mount options.)
    >
    > I worry #1 would have substantial user-space impact, but I don't see a way
    > around it, since there would be no obvious way to associate /dev/ptmx with
    > a filesystem.

    Sukadev


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