[libvirt] [PATCH 11/13] blockjob: query backing file of a disk

[Eric Blake]

Implementing the VIR_DOMAIN_BLOCK_REBASE_SHALLOW flag will require
knowing what the immediate backing file is.  As long as we don't
track the entire backing chain in <domain> XML, the next best that
we can do is to ask qemu.

* src/qemu/qemu_conf.h (qemuDomainDiskInfo): Add member.
* src/qemu/qemu_monitor.c (qemuMonitorGetBlockInfo): Free it, via...
(qemuMonitorBlockInfoFree): ...new helper.
* src/qemu/qemu_monitor_json.c (qemuMonitorJSONGetBlockInfo):
Populate it.
---
 src/qemu/qemu_conf.h         |    1 +
 src/qemu/qemu_monitor.c      |   10 +++++++++-
 src/qemu/qemu_monitor_json.c |   12 ++++++++++++
 3 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
index 482e6d3..a8aefaf 100644
--- a/src/qemu/qemu_conf.h
+++ b/src/qemu/qemu_conf.h
@@ -182,6 +182,7 @@ struct qemuDomainDiskInfo {
     bool locked;
     bool tray_open;
     int io_status;
+    char *backing;
 };

 typedef virDomainObjPtr (*qemuDriverCloseCallback)(struct qemud_driver *driver,
diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index f33bed8..2f5be2e 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -1358,6 +1358,14 @@ qemuMonitorBlockIOStatusToError(const char *status)
     return -1;
 }

+static void
+qemuMonitorBlockInfoFree(void *payload, const void *name ATTRIBUTE_UNUSED)
+{
+    struct qemuDomainDiskInfo *info = payload;
+    VIR_FREE(info->backing);
+    VIR_FREE(info);
+}
+
 virHashTablePtr
 qemuMonitorGetBlockInfo(qemuMonitorPtr mon)
 {
@@ -1372,7 +1380,7 @@ qemuMonitorGetBlockInfo(qemuMonitorPtr mon)
         return NULL;
     }

-    if (!(table = virHashCreate(32, (virHashDataFree) free)))
+    if (!(table = virHashCreate(32, qemuMonitorBlockInfoFree)))
         return NULL;

     if (mon->json)
diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index 3ddeaa3..d24d7e7 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -1532,6 +1532,8 @@ int qemuMonitorJSONGetBlockInfo(qemuMonitorPtr mon,
         struct qemuDomainDiskInfo *info;
         const char *thisdev;
         const char *status;
+        virJSONValuePtr inserted;
+        const char *backing = NULL;

         if (!dev || dev->type != VIR_JSON_TYPE_OBJECT) {
             qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -1584,6 +1586,16 @@ int qemuMonitorJSONGetBlockInfo(qemuMonitorPtr mon,
             if (info->io_status < 0)
                 goto cleanup;
         }
+
+        /* Missing inserted, or inserted with missing backing_file,
+         * indicates no backing file.  */
+        inserted = virJSONValueObjectGet(dev, "inserted");
+        if (inserted)
+            backing = virJSONValueObjectGetString(inserted, "backing_file");
+        if (backing && !(info->backing = strdup(backing))) {
+            virReportOOMError();
+            goto cleanup;
+        }
     }

     ret = 0;
-- 
1.7.7.6