[libvirt] [PATCH 1 of 4] [LXC] Detect support for NETNS in lxc driver initialization
dlezcano at fr.ibm.com
Wed Jun 25 20:49:16 UTC 2008
Dan Smith wrote:
> DL> You call
> DL> clone(CLONE_NEWPID|CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWUSER|CLONE_NEWIPC|SIGCHLD|CLONE_NEWNET)
> DL> When this call fails, you 'assume' netns is not compiled in.
> No, actually, I do this:
> int flags = CLONE_NEWPID|CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWUSER|
> Where extra_flags=0 for the LXC detection and extra_flags=CLONE_NEWNET
> for the NETNS detection. See the lxcCheckContainerSupport() calls in
> lxcProbe() and lxcCheckNetNsSupport().
Did I missed something ?
> DL> In your code, you launch the ip command and if it fails with a
> DL> particular exit code, you 'assume' netns is not supported. Another
> DL> assumption
> The ip command returns a different error code for an invalid
> subcommand than for a failure of a known subcommand. That seems like
> a pretty reasonable sentinel (and certainly better than scraping the
> help output), IMHO.
Who told to scrap the output :)
Just verify the return code of the command.
Anyway, catching a specific return code for an unknown subcommand makes
sense for this check.
> DL> ... IMHO you should rely on the package dependencies/command
> DL> version. Or if you absolutely want to detect that at startup,
> DL> perhaps doing "ip link help | grep netns" is more secure :)
> DV has already said he'd like to see it done dynamically at the driver
> probe stage. I'll let him comment on his preferred way of doing that.
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