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[libvirt] [PATCH] Introduce startupPolicy for chardev to make guest OS bootable when hardware failure happens in log disk



[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, qemu should offer some way to boot guest OS up even if the log 
disk is broken.

[Solution]
This patch supports startupPolicy for chardev.

The starupPolicy is introduced just in case where chardev is "file" 
because this patch aims for making guest OS boot up when a hardware failure happens.

In other cases ,pty, dev, pipe and unix, it is not introduced
because they don't access to hardware.

The policy works as follows.
  - If the value is "optional", guestOS boots up by dropping the chardev.
  - If other values are specified, guestOS fails to boot up. (the default)

Description about original startupPolicy attribute:
http://libvirt.org/git/?p=libvirt.git;a=commitdiff;h=e5a84d74a2789a917bf394f15de9989ec48fded0

Signed-off-by: Seiji Aguchi <seiji aguchi hds com>
---
 docs/formatdomain.html.in     |    9 ++++++++-
 docs/schemas/domaincommon.rng |    3 +++
 src/conf/domain_conf.c        |    8 ++++++++
 src/conf/domain_conf.h        |    1 +
 src/qemu/qemu_process.c       |   25 ++++++++++++++++++++++++-
 tests/virt-aa-helper-test     |    3 +++
 6 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index f325c3c..1e1bf27 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -4044,13 +4044,20 @@ qemu-kvm -net nic,model=? /dev/null
     <p>
       A file is opened and all data sent to the character
       device is written to the file.
+      It is possible to define policy whether guestOS boots up
+      if the file is not accessible. This is done by a startupPolicy
+      attribute:
+      <ul>
+      <li>If the vaule is "optional", guestOS boots up by dropping the file.</li>
+      <li>If other values are specified, guestOS fails to boot up. (the default)</li>
+      </ul>
     </p>
 
 <pre>
   ...
   &lt;devices&gt;
     &lt;serial type="file"&gt;
-      &lt;source path="/var/log/vm/vm-serial.log"/&gt;
+      &lt;source path="/var/log/vm/vm-serial.log" startupPolicy="optional"/&gt;
       &lt;target port="1"/&gt;
     &lt;/serial&gt;
   &lt;/devices&gt;
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 10596dc..6fc0a3c 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -2706,6 +2706,9 @@
         </optional>
         <optional>
           <attribute name="path"/>
+            <optional>
+              <ref name='startupPolicy'/>
+            </optional>
         </optional>
         <optional>
           <attribute name="host"/>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index a8b5dfd..6680f15 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -6467,6 +6467,7 @@ virDomainChrSourceDefParseXML(virDomainChrSourceDefPtr def,
     char *path = NULL;
     char *mode = NULL;
     char *protocol = NULL;
+    char *startupPolicy = NULL;
     int remaining = 0;
 
     while (cur != NULL) {
@@ -6487,6 +6488,9 @@ virDomainChrSourceDefParseXML(virDomainChrSourceDefPtr def,
                          !(flags & VIR_DOMAIN_XML_INACTIVE)))
                         path = virXMLPropString(cur, "path");
 
+                    if (startupPolicy == NULL &&
+                        def->type == VIR_DOMAIN_CHR_TYPE_FILE)
+                        startupPolicy = virXMLPropString(cur, "startupPolicy");
                     break;
 
                 case VIR_DOMAIN_CHR_TYPE_UDP:
@@ -6559,6 +6563,10 @@ virDomainChrSourceDefParseXML(virDomainChrSourceDefPtr def,
 
         def->data.file.path = path;
         path = NULL;
+
+        def->data.file.startupPolicy =
+            virDomainStartupPolicyTypeFromString(startupPolicy);
+        startupPolicy = NULL;
         break;
 
     case VIR_DOMAIN_CHR_TYPE_STDIO:
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 3a0f23a..e709951 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1052,6 +1052,7 @@ struct _virDomainChrSourceDef {
         /* no <source> for null, vc, stdio */
         struct {
             char *path;
+            int startupPolicy; /* enum virDomainStartupPolicy */
         } file; /* pty, file, pipe, or device */
         struct {
             char *host;
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index e75c8c9..6e2f78e 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2442,7 +2442,30 @@ qemuProcessPrepareChardevDevice(virDomainDefPtr def ATTRIBUTE_UNUSED,
         virReportSystemError(errno,
                              _("Unable to pre-create chardev file '%s'"),
                              dev->source.data.file.path);
-        return -1;
+        if (dev->source.data.file.startupPolicy !=
+            VIR_DOMAIN_STARTUP_POLICY_OPTIONAL) {
+            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.
+         */
+        VIR_WARN("Switch the destination to /dev/null");
+        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);
diff --git a/tests/virt-aa-helper-test b/tests/virt-aa-helper-test
index af91c61..7172fd6 100755
--- a/tests/virt-aa-helper-test
+++ b/tests/virt-aa-helper-test
@@ -255,6 +255,9 @@ testme "0" "disk (empty cdrom)" "-r -u $valid_uuid" "$test_xml"
 sed -e "s,###UUID###,$uuid,g" -e "s,###DISK###,$disk1,g" -e "s,</devices>,<serial type='file'><source path='$tmpdir/serial.log'/><target port='0'/></serial></devices>,g" "$template_xml" > "$test_xml"
 testme "0" "serial" "-r -u $valid_uuid" "$test_xml"
 
+sed -e "s,###UUID###,$uuid,g" -e "s,###DISK###,$disk1,g" -e "s,</devices>,<serial type='file'><source path='$tmpdir/serial.log' startupPolicy='optional'/><target port='0'/></serial></devices>,g" "$template_xml" > "$test_xml"
+testme "0" "serial" "-r -u $valid_uuid" "$test_xml"
+
 sed -e "s,###UUID###,$uuid,g" -e "s,###DISK###,$disk1,g" -e "s,</devices>,<serial type='pty'><target port='0'/></serial></devices>,g" "$template_xml" > "$test_xml"
 testme "0" "serial (pty)" "-r -u $valid_uuid" "$test_xml"
 
-- 
1.7.1



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