qemu_process: Make qemuProcessReadLog() more versatile and reusable

Teach the function to skip character device definitions printed by qemu
at startup in addition to libvirt log messages and make it usable from
outside of qemu_process.c. Also add documentation about the func.

src/qemu/qemu_process.c

@@ -1450,8 +1450,20 @@ error:
     return ret;
 }
 
-static int
-qemuProcessReadLog(int fd, char *buf, int buflen, int off)
+
+/**
+ * qemuProcessReadLog: Read log file of a qemu VM
+ * @fd: File descriptor of the log file
+ * @buf: buffer to store the read messages
+ * @buflen: allocated space available in @buf
+ * @off: Offset to start reading from
+ * @skipchar: Skip messages about created character devices
+ *
+ * Reads log of a qemu VM. Skips messages not produced by qemu or irrelevant
+ * messages. Returns length of the message stored in @buf, or -1 on error.
+ */
+int
+qemuProcessReadLog(int fd, char *buf, int buflen, int off, bool skipchar)
 {
     char *filter_next = buf;
     ssize_t bytes;
@@ -1471,7 +1483,9 @@ qemuProcessReadLog(int fd, char *buf, int buflen, int off)
         /* Filter out debug messages from intermediate libvirt process */
         while ((eol = strchr(filter_next, '\n'))) {
             *eol = '\0';
-            if (virLogProbablyLogMessage(filter_next)) {
+            if (virLogProbablyLogMessage(filter_next) ||
+                (skipchar &&
+                 STRPREFIX(filter_next, "char device redirected to"))) {
                 memmove(filter_next, eol + 1, off - (eol - buf));
                 off -= eol + 1 - filter_next;
             } else {
@@ -1514,7 +1528,7 @@ qemuProcessReadLogOutput(virDomainObjPtr vm,
 
         isdead = kill(vm->pid, 0) == -1 && errno == ESRCH;
 
-        got = qemuProcessReadLog(fd, buf, buflen, got);
+        got = qemuProcessReadLog(fd, buf, buflen, got, false);
         if (got < 0) {
             virReportSystemError(errno,
                                  _("Failure while reading %s log output"),
@@ -1832,7 +1846,7 @@ cleanup:
         }
 
         len = strlen(buf);
-        qemuProcessReadLog(logfd, buf + len, buf_size - len - 1, 0);
+        qemuProcessReadLog(logfd, buf + len, buf_size - len - 1, 0, true);
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("process exited while connecting to monitor: %s"),
                        buf);

src/qemu/qemu_process.h

@@ -101,4 +101,6 @@ bool qemuProcessAutoDestroyActive(virQEMUDriverPtr driver,
 virBitmapPtr qemuPrepareCpumap(virQEMUDriverPtr driver,
                                virBitmapPtr nodemask);
 
+int qemuProcessReadLog(int fd, char *buf, int buflen, int off, bool skipchar);
+
 #endif /* __QEMU_PROCESS_H__ */