Re: [libvirt] [RFC] Create ptmx as a device

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(a)domU-12-31-39-14-F0-B3.compute-1.internal&gt; > 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(a)canonical.com&gt; > --- > 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.