From 0b0135f00c4e17cb902ec6885648b5a4e667d56b Mon Sep 17 00:00:00 2001

Message-Id: <0b0135f00c4e17cb902ec6885648b5a4e667d56b@dist-git>

From: Jiri Denemark <jdenemar@redhat.com>

Date: Wed, 22 Nov 2017 13:12:00 +0100

Subject: [PATCH] qemu: Use the end of QEMU log for reporting errors

When QEMU dies, we read its output stored in a log file and use it for

reporting a hopefully useful error. However, virReportError will trim

the message to (VIR_ERROR_MAX_LENGTH - 1) characters, which means the

end of the log (which likely contains the error message we want to

report) may get lost. We should trim the beginning of the log instead.

https://bugzilla.redhat.com/show_bug.cgi?id=1335534

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

(cherry picked from commit 96f7a045e93ad08eb4130be97dd6d8a8c963a952)

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

---

 src/qemu/qemu_process.c | 34 ++++++++++++++++++++++++++++++----

 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c

index c5fa8cb4b2..f7808227a8 100644

--- a/src/qemu/qemu_process.c

+++ b/src/qemu/qemu_process.c

@@ -1827,17 +1827,24 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int asyncJob,

  * qemuProcessReadLog: Read log file of a qemu VM

  * @logCtxt: the domain log context

  * @msg: pointer to buffer to store the read messages in

+ * @max: maximum length of the message returned in @msg

  *

  * Reads log of a qemu VM. Skips messages not produced by qemu or irrelevant

- * messages. Returns returns 0 on success or -1 on error

+ * messages. If @max is not zero, @msg will contain at most @max characters

+ * from the end of the log and @msg will start after a new line if possible.

+ *

+ * Returns 0 on success or -1 on error

  */

 static int

-qemuProcessReadLog(qemuDomainLogContextPtr logCtxt, char **msg)

+qemuProcessReadLog(qemuDomainLogContextPtr logCtxt,

+                   char **msg,

+                   size_t max)

 {

     char *buf;

     ssize_t got;

     char *eol;

     char *filter_next;

+    size_t skip;

     if ((got = qemuDomainLogContextRead(logCtxt, &buf)) < 0)

         return -1;

@@ -1848,7 +1855,7 @@ qemuProcessReadLog(qemuDomainLogContextPtr logCtxt, char **msg)

         *eol = '\0';

         if (virLogProbablyLogMessage(filter_next) ||

             strstr(filter_next, "char device redirected to")) {

-            size_t skip = (eol + 1) - filter_next;

+            skip = (eol + 1) - filter_next;

             memmove(filter_next, eol + 1, buf + got - eol);

             got -= skip;

         } else {

@@ -1863,6 +1870,19 @@ qemuProcessReadLog(qemuDomainLogContextPtr logCtxt, char **msg)

         buf[got - 1] = '\0';

         got--;

     }

+

+    if (max > 0 && got > max) {

+        skip = got - max;

+

+        if (buf[skip - 1] != '\n' &&

+            (eol = strchr(buf + skip, '\n')) &&

+            !virStringIsEmpty(eol + 1))

+            skip = eol + 1 - buf;

+

+        memmove(buf, buf + skip, got - skip + 1);

+        got -= skip;

+    }

+

     ignore_value(VIR_REALLOC_N_QUIET(buf, got + 1));

     *msg = buf;

     return 0;

@@ -1874,8 +1894,14 @@ qemuProcessReportLogError(qemuDomainLogContextPtr logCtxt,

                           const char *msgprefix)

 {

     char *logmsg = NULL;

+    size_t max;

-    if (qemuProcessReadLog(logCtxt, &logmsg) < 0)

+    max = VIR_ERROR_MAX_LENGTH - 1;

+    max -= strlen(msgprefix);

+    /* The length of the formatting string minus two '%s' */

+    max -= strlen(_("%s: %s")) - 4;

+

+    if (qemuProcessReadLog(logCtxt, &logmsg, max) < 0)

         return -1;

     virResetLastError();

-- 

2.15.0