[libvirt] [PATCHv2 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.
---
Notes:
Version 2:
- fixed typos
- avoided unnecessary reset of error
- removed unneeded strlen to check returned log string
src/qemu/qemu_monitor.c | 66 ++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 60 insertions(+), 6 deletions(-)
diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index c3701fe..a601ee0 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 +333,35 @@ 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_QUIET(logbuf, 4096) < 0)
+ goto error;
+
+ if ((len = qemuProcessReadLog(mon->logfd, logbuf, 4096 - 1, 0, true)) <= 0)
+ goto error;
+
+cleanup:
+ errno = orig_errno;
+ VIR_FORCE_CLOSE(mon->logfd);
+ return logbuf;
+
+error:
+ VIR_FREE(logbuf);
+ goto cleanup;
+}
+
+
/* This method processes data that has been received
* from the monitor. Looking for async events and
* replies/errors.
@@ -564,6 +595,7 @@ 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 +646,14 @@ 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 +672,26 @@ 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 in early
+ * startup phases where the message from qemu is certainly more
+ * interesting than a "connection reset by peer" message.
+ */
+ char *qemuMessage;
+
+ if ((qemuMessage = qemuMonitorGetErrorFromLog(mon))) {
+ 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();
--
1.8.3.2