On 02/07/2014 08:33 AM, Daniel P. Berrange wrote:
Implement virProcessRunInMountNamespace, which runs callback of type virProcessNamespaceCallback in a container namespace. This uses a child process to run the callback, since you can't change the mount namespace of a thread. This implies that callbacks have to be careful about what code they run due to async safety rules.
Idea by Dan Berrange, based on an initial report by Reco <recoverym4n@gmail.com> at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=732394
Signed-off-by: Daniel Berrange <berrange@redhat.com>
Looks like you improved from my version, so it would be nice to add: Signed-off-by: Eric Blake <eblake@redhat.com>
+ +/* Run cb(opaque) in the mount namespace of pid. Return -1 with error + * message raised if we fail to run the child, if the child dies from + * a signal, or if the child has status EXIT_CANCELED; otherwise
Comment is wrong, since EXIT_CANCELED is not defined yet (it will be fixed when I rebase the virFork cleanups on top of this).
+ if (ret < 0 || child < 0) { + if (child == 0) + _exit(1);
Similarly, I prefer EXIT_FAILURE over the magic '1'. But I don't mind cleaning that up in my rebased virFork stuff.
+ else if (child > 0)
The else is redundant, since _exit() never returns.
+ if (child == 0) { + VIR_FORCE_CLOSE(errfd[0]); + ret = virProcessNamespaceHelper(errfd[1], pid, + cb, opaque); + VIR_FORCE_CLOSE(errfd[1]); + _exit(ret < 0 ? 1 : 0);
Again, more magic numbers I can clean up later.
+ + ignore_value(virFileReadHeaderFD(errfd[0], 1024, &buf)); + if (virProcessWait(child, &status) < 0) + ret = -1; + else + ret = status == 0 ? 0 : -1;
This can be simplified: ret = virProcessWait(child, NULL);
+ if (ret < 0) + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", + buf ? buf : _("Failed to run callback in mount namespace"));
And this error message overwrites the error from virProcessWait.
+/* Callback to run code within the mount namespace tied to the given + * pid. This function must use only async-signal-safe functions, as + * it gets run after a fork of a multi-threaded process. The return + * value of this function is passed to _exit(), except that a + * negative value is treated as EXIT_CANCELED. */ +typedef int (*virProcessNamespaceCallback)(pid_t pid, void *opaque);
Again, the comment doesn't quite work with the rearranged patch order. My comments above are improvements, but I didn't spot any bugs in your implementation. ACK. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org