Re: [libvirt] [PATCH] Fix reporting of i/o errors by iohelper process

On 07/16/2014 03:56 PM, Eric Blake wrote: Okay, looking into this a bit more: I made the following change: diff --git i/src/util/iohelper.c w/src/util/iohelper.c index 8a3c377..dfb45e1 100644 --- i/src/util/iohelper.c +++ w/src/util/iohelper.c @@ -307,6 +307,7 @@ main(int argc, char **argv) if (delete) unlink(path); + fprintf(stderr, _("goodbye world\n")); goto error; return 0; error: then tried to do a 'virsh save testvm1 /tmp/save'. Even without your patch, I get a very nice error: error: Failed to save domain testvm1 to /tmp/save error: internal error: Child process (LIBVIRT_LOG_OUTPUTS=1:stderr /home/eblake/libvirt/src/libvirt_iohelper /tmp/save 0 1) unexpected exit status 1: goodbye world /home/eblake/libvirt/src/libvirt_iohelper: unknown failure with /tmp/save But if I then rework the iohelper patch: diff --git i/src/util/iohelper.c w/src/util/iohelper.c index 8a3c377..efb1366 100644 --- i/src/util/iohelper.c +++ w/src/util/iohelper.c @@ -301,6 +301,7 @@ main(int argc, char **argv) exit(EXIT_FAILURE); } + fprintf(stderr, _("goodbye world\n")); goto error; if (fd < 0 || runIO(path, fd, oflags, length) < 0) goto error; the error is now: error: Failed to save domain testvm1 to /tmp/save error: operation failed: domain save job: unexpectedly failed So the problem is that we have _two_ possible sources of errors (qemu reporting failure because it can't write to iohelper, and iohelper reporting an error from whatever other reason, such as disk full). If qemu finishes, we have only the iohelper message and properly report it; but if we have both failures, then the qemu error takes priority, and in this case it is lower priority. There are also cases where qemu will error out but iohelper succeeds (such as if qemu refuses to migrate because the guest has hostdev passthrough). So I _think_ what we want to do is always check BOTH places for error; if only one of the two fails, use that message. If both fail, then I don't know whether it is possible to have a heuristic for which failure message is more meaningful, or whether it is better to report both errors (even though it will often be the case that one error was a knock-on effect from the other). But I'm a bit stuck on the best way to implement that. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org