[Bug 1197754] [NEW] "lxc-start-ephemeral -d" is racy

[Serge Hallyn]

Quoting Robie Basak (1197754 at bugs.launchpad.net):
> Public bug reported:
> 
> A script cannot call lxc-start-ephemeral and get a named container in a
> reliable, race-free way.
> 
> Having the caller specify a name directly is racy, since the name could
> have been taken in between checking that it doesn't exist already and
> calling lxc-start-ephemeral.

Practically speaking, have you actually created the container name with
mktemp (i.e. mktemp -u -t lxc-XXXXXX | sed 's@/tmp/@@') and gotten name
clashes?

> Allowing lxc-start-ephemeral allows it to take care of the mkdir (and
> retries) to generate an LXC container name in a race free manner, but
> this needs -d to return the name in a machine-readable way, so that we
> can create ephemeral LXC containers from scripts.
> 
> Please add a machine-readable mechanism to "lxc-start-ephemeral -d" and
> then we can modify adt-virt-lxc to use it.

That does sound like a good idea - we could add a '--terse' suboption to
-d to only print '$name $ip'

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https://bugs.launchpad.net/bugs/1197754

Title:
  "lxc-start-ephemeral -d" is racy

Status in “autopkgtest” package in Ubuntu:
  New
Status in “lxc” package in Ubuntu:
  New

Bug description:
  A script cannot call lxc-start-ephemeral and get a named container in
  a reliable, race-free way.

  Having the caller specify a name directly is racy, since the name
  could have been taken in between checking that it doesn't exist
  already and calling lxc-start-ephemeral.

  Allowing lxc-start-ephemeral allows it to take care of the mkdir (and
  retries) to generate an LXC container name in a race free manner, but
  this needs -d to return the name in a machine-readable way, so that we
  can create ephemeral LXC containers from scripts.

  Please add a machine-readable mechanism to "lxc-start-ephemeral -d"
  and then we can modify adt-virt-lxc to use it.

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