[libvirt] PATCH Fix QEMU monitor prompt confusion

When you first connect to the QEMU monitor after a VM starts, it will print out QEMU 0.10.5 monitor - type 'help' for more information We already have code to detect & discard this. Unfortunately it seems that with QEMU >= 0.10.0 it will also print out this prompt when you disconnect and reconnect to the QEMU monitor. Except it doesn't print this out every time. It only appears to happen 50% of the time when libvirtd restarts and reconnects. When it does happen though it totally breaks all future monitor commands libvirt tries to run. This patch takes a fairly simple approach to solving it. Before running any QEMU monitor command, read and discard all pending data. 99% of the time there will be none, but if there is, this saves us from disaster. Daniel diff --git a/src/qemu_driver.c b/src/qemu_driver.c index 95ea882..fdbbb56 100644 --- a/src/qemu_driver.c +++ b/src/qemu_driver.c @@ -1656,6 +1656,28 @@ cleanup: qemuDriverUnlock(driver); } + +/* Throw away any data available on the monitor + * This is done before executing a command, in order + * to allow re-synchronization if something went badly + * wrong in the past. it also deals with problem of + * QEMU *sometimes* re-printing its initial greeting + * when we reconnect to the monitor after restarts. + */ +static void +qemuMonitorDiscardPendingData(virDomainObjPtr vm) { + char buf[1024]; + int ret = 0; + + /* Monitor is non-blocking, so just loop till we + * get -1 or 0. Don't bother with detecting + * errors, since we'll deal with that better later */ + do { + ret = read(vm->monitor, buf, sizeof (buf)-1); + } while (ret > 0); +} + + static int qemudMonitorCommandExtra(const virDomainObjPtr vm, const char *cmd, @@ -1667,6 +1689,8 @@ qemudMonitorCommandExtra(const virDomainObjPtr vm, size_t cmdlen = strlen(cmd); size_t extralen = extra ? strlen(extra) : 0; + qemuMonitorDiscardPendingData(vm); + if (safewrite(vm->monitor, cmd, cmdlen) != cmdlen) return -1; if (safewrite(vm->monitor, "\r", 1) != 1) -- 1.6.2.5 -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|