Quoting Daniel Veillard (veillard@xxxxxxxxxx):
> On Wed, Aug 31, 2011 at 01:18:33PM -0500, Serge Hallyn wrote:
> > Hi,
> >
> > I'm seeing an issue with udev and libvirt-lxc. Libvirt-lxc creates
> > /dev/ptmx as a symlink to /dev/pts/ptmx. When udev starts up, it
> > checks the device type, sees ptmx is 'not right', and replaces it
> > with a 'proper' ptmx.
> >
> > In lxc, /dev/ptmx is bind-mounted from /dev/pts/ptmx instead of being
> > symlinked, so udev sees the right device type and leaves it alone.
> >
> > A patch like the following seems to work for me. Would there be
> > any objections to this?
> >
> > >From 4c5035de52de7e06a0de9c5d0bab8c87a806cba7 Mon Sep 17 00:00:00 2001
> > From: Ubuntu <ubuntu@domU-12-31-39-14-F0-B3.compute-1.internal>
> > Date: Wed, 31 Aug 2011 18:15:54 +0000
> > Subject: [PATCH 1/1] make ptmx a bind mount rather than symlink
> >
> > udev on some systems checks the device type of /dev/ptmx, and replaces it if
> > not as expected. The symlink created by libvirt-lxc therefore gets replaced.
> > By creating it as a bind mount, the device type is correct and udev leaves it
> > alone.
> >
> > Signed-off-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> > ---
> > src/lxc/lxc_container.c | 20 ++++++++++----------
> > 1 files changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
> > index e425328..6991aec 100644
> > --- a/src/lxc/lxc_container.c
> > +++ b/src/lxc/lxc_container.c
> > @@ -543,18 +543,18 @@ static int lxcContainerPopulateDevices(void)
> > }
> > }
> >
> > + dev_t dev = makedev(LXC_DEV_MAJ_TTY, LXC_DEV_MIN_PTMX);
> > + if (mknod("/dev/ptmx", S_IFCHR, dev) < 0 ||
> > + chmod("/dev/ptmx", 0666)) {
> > + virReportSystemError(errno, "%s",
> > + _("Failed to make device /dev/ptmx"));
> > + return -1;
> > + }
> > +
> > if (access("/dev/pts/ptmx", W_OK) == 0) {
> > - if (symlink("/dev/pts/ptmx", "/dev/ptmx") < 0) {
> > - virReportSystemError(errno, "%s",
> > - _("Failed to create symlink /dev/ptmx to /dev/pts/ptmx"));
> > - return -1;
> > - }
> > - } else {
> > - dev_t dev = makedev(LXC_DEV_MAJ_TTY, LXC_DEV_MIN_PTMX);
> > - if (mknod("/dev/ptmx", S_IFCHR, dev) < 0 ||
> > - chmod("/dev/ptmx", 0666)) {
> > + if (mount("/dev/pts/ptmx", "/dev/ptmx", "ptmx", MS_BIND, NULL) < 0) {
> > virReportSystemError(errno, "%s",
> > - _("Failed to make device /dev/ptmx"));
> > + _("Failed to bind-mount /dev/ptmx to /dev/pts/ptmx"));
> > return -1;
> > }
> > }
>
> Hum, if we do a mount, I would expect to do an unmount somewhere.
> Also the lifetime of the mount and the symlink is really different,
> a recursive remove when destroying the container would lead to no
> resource leak but I think that for a bind mount we absolutely have
> to clean it up.
This code is being done in a private mount namespace, so the mount will
get automatically cleaned up when that namespace exits.
thanks,
-serge
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