Re: [libvirt] [PATCH 1 of 4] [LXC] Detect support for NETNS in lxc driver initialization
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|
CLONE_NEWIPC|SIGCHLD|extra_flags;
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().
lxcCheckContainerSupport(0)
=> clone(CLONE_NEWPID|
CLONE_NEWNS|
CLONE_NEWUTS|
CLONE_NEWUSER|
CLONE_NEWIPC|
SIGCHLD);
lxcCheckNetNsSupport()
=> lxcCheckContainerSupport(CLONE_NEWNET)
=> clone(CLONE_NEWPID|
CLONE_NEWNS|
CLONE_NEWUTS|
CLONE_NEWUSER|
CLONE_NEWIPC|
SIGCHLD|CLONE_NEWNET);
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.