Re: [libvirt] [PATCH 3/4] qemu: monitor: Produce better errors on monitor hangup

Change the monitor error code to add the ability to access the qemu log file using a file descriptor so that we can dig in it for a more useful error message. The error is now logged on monitor hangups and overwrites a possible lesser error. A hangup on the monitor usualy means that qemu has crashed and there's a significant chance it produced a useful error message. The functionality will be latent until the next patch. --- src/qemu/qemu_monitor.c | 70 ++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 64 insertions(+), 6 deletions(-) diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c index c3701fe..5369975 100644 --- a/src/qemu/qemu_monitor.c +++ b/src/qemu/qemu_monitor.c @@ -32,6 +32,8 @@ #include "qemu_monitor.h" #include "qemu_monitor_text.h" #include "qemu_monitor_json.h" +#include "qemu_domain.h" +#include "qemu_process.h" #include "virerror.h" #include "viralloc.h" #include "virlog.h" @@ -331,6 +333,37 @@ qemuMonitorOpenPty(const char *monitor) } +/* Get a possible error from qemu's log. This function closes the + * corresponding log fd */ +static char * +qemuMonitorGetErrorFromLog(qemuMonitorPtr mon) +{ + int len; + char *logbuf = NULL; + int orig_errno = errno; + + if (mon->logfd < 0) + return NULL; + + if (VIR_ALLOC_N(logbuf, 4096) < 0) + goto error; + + if ((len = qemuProcessReadLog(mon->logfd, logbuf, 4096 - 1, 0, true)) <= 0) + goto error; + + errno = orig_errno; + VIR_FORCE_CLOSE(mon->logfd); + return logbuf; + +error: + virResetLastError();

+ VIR_FREE(logbuf); + VIR_FORCE_CLOSE(mon->logfd); + errno = orig_errno; + return NULL; +} + + /* This method processes data that has been received * from the monitor. Looking for async events and * replies/errors. @@ -564,6 +597,7 @@ qemuMonitorIO(int watch, int fd, int events, void *opaque) { qemuMonitorPtr mon = opaque; bool error = false; bool eof = false; + bool hangup = false; virObjectRef(mon); @@ -614,12 +648,14 @@ qemuMonitorIO(int watch, int fd, int events, void *opaque) { } } - if (!error && - events & VIR_EVENT_HANDLE_HANGUP) { - virReportError(VIR_ERR_INTERNAL_ERROR, "%s", - _("End of file from monitor")); - eof = true; - events &= ~VIR_EVENT_HANDLE_HANGUP; + if (events & VIR_EVENT_HANDLE_HANGUP) { + hangup = true; + if (!error) { + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", + _("End of file from monitor")); + eof = true; + events &= ~VIR_EVENT_HANDLE_HANGUP; + } } if (!error && !eof && @@ -638,6 +674,28 @@ qemuMonitorIO(int watch, int fd, int events, void *opaque) { } if (error || eof) { + if (hangup) { + /* Check if an error message from qemu is available and if so, use + * it to overwrite the actual message. It's done only on early

+ * startup phases where the message from qemu is certailny more

+ * interresting than a "connection reset by peer" message.

+ */ + char *qemuMessage; + + if ((qemuMessage = qemuMonitorGetErrorFromLog(mon)) && + strlen(qemuMessage) > 0) {

+ + virReportError(VIR_ERR_INTERNAL_ERROR, + _("early end of file from monitor: " + "possible problem:\n%s"), + qemuMessage); + virCopyLastError(&mon->lastError); + virResetLastError(); + } + + VIR_FREE(qemuMessage); + } + if (mon->lastError.code != VIR_ERR_OK) { /* Already have an error, so clear any new error */ virResetLastError();