[libvirt] [PATCH] Make guest OS bootable when hardware failure happens in log disk

[Seiji Aguchi]

[Problem]
Currently, guest OS's messages can be logged to a local disk of host OS 
by creating chadevs with options below.
  -chardev file,id=charserial0,path=<log file's path> -device isa-serial,chardev=chardevserial0,id=serial0

When a hardware failure happens in the disk, qemu-kvm can't create the chardevs.
In this case, guest OS doesn't boot up.

Actually, there are users who don't desire that guest OS goes down due to a hardware failure 
of a log disk only.Therefore, libvirt should offer some way to boot guest OS up even if the log 
disk is broken.

[Solution]
This patch changes a destination to /dev/null in case a log file can't be opened.

Signed-off-by: Seiji Aguchi <seiji.aguchi at hds.com>
---
 src/qemu/qemu_process.c |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 8c4bfb7..fdf26ad 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2440,7 +2440,25 @@ qemuProcessPrepareChardevDevice(virDomainDefPtr def ATTRIBUTE_UNUSED,
         virReportSystemError(errno,
                              _("Unable to pre-create chardev file '%s'"),
                              dev->source.data.file.path);
-        return -1;
+        VIR_FREE(dev->source.data.file.path);
+        /*
+         *  Change a destination to /dev/null to boot guest OS up
+         *  even if a log disk is broken.
+         */
+        dev->source.data.file.path = strdup("/dev/null");
+
+        if (!dev->source.data.file.path) {
+            virReportOOMError();
+            return -1;
+        }
+
+        if ((fd = open(dev->source.data.file.path,
+                       O_CREAT | O_APPEND, S_IRUSR|S_IWUSR)) < 0) {
+            virReportSystemError(errno,
+                                 _("Unable to pre-create chardev file '%s'"),
+                                 dev->source.data.file.path);
+            return -1;
+        }
     }
 
     VIR_FORCE_CLOSE(fd);
-- 1.7.1