qemu: read backing chain names from qemu

https://bugzilla.redhat.com/show_bug.cgi?id=1199182 documents that
after a series of disk snapshots into existing destination images,
followed by active commits of the top image, it is possible for
qemu 2.2 and earlier to end up tracking a different name for the
image than what it would have had when opening the chain afresh.
That is, when starting with the chain 'a <- b <- c', the name
associated with 'b' is how it was spelled in the metadata of 'c',
but when starting with 'a', taking two snapshots into 'a <- b <- c',
then committing 'c' back into 'b', the name associated with 'b' is
now the name used when taking the first snapshot.

Sadly, older qemu doesn't know how to treat different spellings of
the same filename as identical files (it uses strcmp() instead of
checking for the same inode), which means libvirt's attempt to
commit an image using solely the names learned from qcow2 metadata
fails with a cryptic:

error: internal error: unable to execute QEMU command 'block-commit': Top image file /tmp/images/c/../b/b not found

even though the file exists.  Trying to teach libvirt the rules on
which name qemu will expect is not worth the effort (besides, we'd
have to remember it across libvirtd restarts, and track whether a
file was opened via metadata or via snapshot creation for a given
qemu process); it is easier to just always directly ask qemu what
string it expects to see in the first place.

As a safety valve, we validate that any name returned by qemu
still maps to the same local file as we have tracked it, so that
a compromised qemu cannot accidentally cause us to act on an
incorrect file.

* src/qemu/qemu_monitor.h (qemuMonitorDiskNameLookup): New
prototype.
* src/qemu/qemu_monitor_json.h (qemuMonitorJSONDiskNameLookup):
Likewise.
* src/qemu/qemu_monitor.c (qemuMonitorDiskNameLookup): New function.
* src/qemu/qemu_monitor_json.c (qemuMonitorJSONDiskNameLookup)
(qemuMonitorJSONDiskNameLookupOne): Likewise.
* src/qemu/qemu_driver.c (qemuDomainBlockCommit)
(qemuDomainBlockJobImpl): Use it.

Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit f9ea3d60119e82c02c00fbf3678c3ed20634dea1)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index e2824643f00ca5925b239b91d97598d500bbd7c6..2738518b9c5b34cd104fe7fc5e06aad07ce105e2 100644 (file)
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -15788,9 +15788,6 @@ qemuDomainBlockJobImpl(virDomainObjPtr vm,
         goto endjob;
 
     if (baseSource) {
-        if (qemuGetDriveSourceString(baseSource, NULL, &basePath) < 0)
-            goto endjob;
-
         if (flags & VIR_DOMAIN_BLOCK_REBASE_RELATIVE) {
             if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_CHANGE_BACKING_FILE)) {
                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
@@ -15828,8 +15825,12 @@ qemuDomainBlockJobImpl(virDomainObjPtr vm,
     }
 
     qemuDomainObjEnterMonitor(driver, vm);
-    ret = qemuMonitorBlockJob(priv->mon, device, basePath, backingPath,
-                              speed, mode, async);
+    if (baseSource)
+        basePath = qemuMonitorDiskNameLookup(priv->mon, device, disk->src,
+                                             baseSource);
+    if (!baseSource || basePath)
+        ret = qemuMonitorBlockJob(priv->mon, device, basePath, backingPath,
+                                  speed, mode, async);
     if (qemuDomainObjExitMonitor(driver, vm) < 0)
         ret = -1;
     if (ret < 0) {
@@ -16559,12 +16560,6 @@ qemuDomainBlockCommit(virDomainPtr dom,
                                            VIR_DISK_CHAIN_READ_WRITE) < 0))
         goto endjob;
 
-    if (qemuGetDriveSourceString(topSource, NULL, &topPath) < 0)
-        goto endjob;
-
-    if (qemuGetDriveSourceString(baseSource, NULL, &basePath) < 0)
-        goto endjob;
-
     if (flags & VIR_DOMAIN_BLOCK_COMMIT_RELATIVE &&
         topSource != disk->src) {
         if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_CHANGE_BACKING_FILE)) {
@@ -16595,9 +16590,14 @@ qemuDomainBlockCommit(virDomainPtr dom,
         disk->mirrorJob = VIR_DOMAIN_BLOCK_JOB_TYPE_ACTIVE_COMMIT;
     }
     qemuDomainObjEnterMonitor(driver, vm);
-    ret = qemuMonitorBlockCommit(priv->mon, device,
-                                 topPath, basePath, backingPath,
-                                 speed);
+    basePath = qemuMonitorDiskNameLookup(priv->mon, device, disk->src,
+                                         baseSource);
+    topPath = qemuMonitorDiskNameLookup(priv->mon, device, disk->src,
+                                        topSource);
+    if (basePath && topPath)
+        ret = qemuMonitorBlockCommit(priv->mon, device,
+                                     topPath, basePath, backingPath,
+                                     speed);
     if (qemuDomainObjExitMonitor(driver, vm) < 0) {
         ret = -1;
         goto endjob;

diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index 94495cd7179b242e02434cd922bb6a7776ad381d..15b136074c49c2896a9974074ed358e619d86136 100644 (file)
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -3488,6 +3488,24 @@ qemuMonitorSupportsActiveCommit(qemuMonitorPtr mon)
 }
 
 
+/* Determine the name that qemu is using for tracking the backing
+ * element TARGET within the chain starting at TOP.  */
+char *
+qemuMonitorDiskNameLookup(qemuMonitorPtr mon,
+                          const char *device,
+                          virStorageSourcePtr top,
+                          virStorageSourcePtr target)
+{
+    if (!mon->json) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                       _("JSON monitor is required"));
+        return NULL;
+    }
+
+    return qemuMonitorJSONDiskNameLookup(mon, device, top, target);
+}
+
+
 /* Use the block-job-complete monitor command to pivot a block copy
  * job.  */
 int

diff --git a/src/qemu/qemu_monitor.h b/src/qemu/qemu_monitor.h
index 133d42d4bb7589e9027d6ec440236ec6738f224e..adcc6747b11460f502ae49c4146073fe80839338 100644 (file)
--- a/src/qemu/qemu_monitor.h
+++ b/src/qemu/qemu_monitor.h
@@ -1,7 +1,7 @@
 /*
  * qemu_monitor.h: interaction with QEMU monitor console
  *
- * Copyright (C) 2006-2014 Red Hat, Inc.
+ * Copyright (C) 2006-2015 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -749,6 +749,12 @@ int qemuMonitorBlockCommit(qemuMonitorPtr mon,
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3)
     ATTRIBUTE_NONNULL(4);
 bool qemuMonitorSupportsActiveCommit(qemuMonitorPtr mon);
+char *qemuMonitorDiskNameLookup(qemuMonitorPtr mon,
+                                const char *device,
+                                virStorageSourcePtr top,
+                                virStorageSourcePtr target)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3)
+    ATTRIBUTE_NONNULL(4);
 
 int qemuMonitorArbitraryCommand(qemuMonitorPtr mon,
                                 const char *cmd,

diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index 832f5898b22c1d53967c37ac6c71c1929d09e47c..73150879f4e91d77e5cf350de6ab243e767453b8 100644 (file)
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -1,7 +1,7 @@
 /*
  * qemu_monitor_json.c: interaction with QEMU monitor console
  *
- * Copyright (C) 2006-2014 Red Hat, Inc.
+ * Copyright (C) 2006-2015 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -4060,6 +4060,106 @@ qemuMonitorJSONDrivePivot(qemuMonitorPtr mon, const char *device,
 }
 
 
+static char *
+qemuMonitorJSONDiskNameLookupOne(virJSONValuePtr image,
+                                 virStorageSourcePtr top,
+                                 virStorageSourcePtr target)
+{
+    virJSONValuePtr backing;
+    char *ret;
+
+    /* The caller will report a generic message if we return NULL
+     * without an error; but in some cases we can improve by reporting
+     * a more specific message.  */
+    if (!top || !image)
+        return NULL;
+    if (top != target) {
+        backing = virJSONValueObjectGet(image, "backing-image");
+        return qemuMonitorJSONDiskNameLookupOne(backing, top->backingStore,
+                                                target);
+    }
+    if (VIR_STRDUP(ret, virJSONValueObjectGetString(image, "filename")) < 0)
+        return NULL;
+    /* Sanity check - the name qemu gave us should resolve to the same
+       file tracked by our target description. */
+    if (virStorageSourceIsLocalStorage(target) &&
+        STRNEQ(ret, target->path) &&
+        !virFileLinkPointsTo(ret, target->path)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("qemu block name '%s' doesn't match expected '%s'"),
+                       ret, target->path);
+        VIR_FREE(ret);
+    }
+    return ret;
+}
+
+
+char *
+qemuMonitorJSONDiskNameLookup(qemuMonitorPtr mon,
+                              const char *device,
+                              virStorageSourcePtr top,
+                              virStorageSourcePtr target)
+{
+    char *ret = NULL;
+    virJSONValuePtr cmd = NULL;
+    virJSONValuePtr reply = NULL;
+    virJSONValuePtr devices;
+    size_t i;
+
+    cmd = qemuMonitorJSONMakeCommand("query-block", NULL);
+    if (!cmd)
+        return NULL;
+    if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
+        goto cleanup;
+
+    devices = virJSONValueObjectGet(reply, "return");
+    if (!devices || devices->type != VIR_JSON_TYPE_ARRAY) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("block info reply was missing device list"));
+        goto cleanup;
+    }
+
+    for (i = 0; i < virJSONValueArraySize(devices); i++) {
+        virJSONValuePtr dev = virJSONValueArrayGet(devices, i);
+        virJSONValuePtr inserted;
+        virJSONValuePtr image;
+        const char *thisdev;
+
+        if (!dev || dev->type != VIR_JSON_TYPE_OBJECT) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("block info device entry was not in expected format"));
+            goto cleanup;
+        }
+
+        if (!(thisdev = virJSONValueObjectGetString(dev, "device"))) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("block info device entry was not in expected format"));
+            goto cleanup;
+        }
+
+        if (STREQ(thisdev, device)) {
+            if ((inserted = virJSONValueObjectGet(dev, "inserted")) &&
+                (image = virJSONValueObjectGet(inserted, "image"))) {
+                ret = qemuMonitorJSONDiskNameLookupOne(image, top, target);
+            }
+            break;
+        }
+    }
+    /* Guarantee an error when returning NULL, but don't override a
+     * more specific error if one was already generated.  */
+    if (!ret && !virGetLastError())
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("unable to find backing name for device %s"),
+                       device);
+
+ cleanup:
+    virJSONValueFree(cmd);
+    virJSONValueFree(reply);
+
+    return ret;
+}
+
+
 int qemuMonitorJSONArbitraryCommand(qemuMonitorPtr mon,
                                     const char *cmd_str,
                                     char **reply_str,

diff --git a/src/qemu/qemu_monitor_json.h b/src/qemu/qemu_monitor_json.h
index 1da1a007ffc0dd712a65f2cb7946f8c5ff060eef..252f8bee28483fa535dffaaf7f0cb44d249eac5c 100644 (file)
--- a/src/qemu/qemu_monitor_json.h
+++ b/src/qemu/qemu_monitor_json.h
@@ -1,7 +1,7 @@
 /*
  * qemu_monitor_json.h: interaction with QEMU monitor console
  *
- * Copyright (C) 2006-2009, 2011-2014 Red Hat, Inc.
+ * Copyright (C) 2006-2009, 2011-2015 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -290,6 +290,13 @@ int qemuMonitorJSONBlockCommit(qemuMonitorPtr mon,
                                unsigned long long bandwidth)
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
 
+char *qemuMonitorJSONDiskNameLookup(qemuMonitorPtr mon,
+                                    const char *device,
+                                    virStorageSourcePtr top,
+                                    virStorageSourcePtr target)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3)
+    ATTRIBUTE_NONNULL(4);
+
 int qemuMonitorJSONArbitraryCommand(qemuMonitorPtr mon,
                                     const char *cmd_str,
                                     char **reply_str,