Re: [libvirt] [PATCH 08/14] Add helper for running code in separate namespaces
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(a)gmail.com> at
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=732394
Signed-off-by: Daniel Berrange <berrange(a)redhat.com>
Looks like you improved from my version, so it would be nice to add:
Signed-off-by: Eric Blake <eblake(a)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
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