[Qemu-devel] [PATCH 15/16] block/parallels: support read-only parallels snapshots

["Denis V. Lunev" <den@openvz.org>]

This patch reads snapshot information from the XML descriptor file.

The lastest snapshot (read-write one) could be located using the
following rules:
GUID could be used as a source to locate leaf in the snapshot tree:
- TopGUID tag is specified in the XML file
- {704718E1-2314-44c8-9087-D78ED36B0F4E} snapshot is present. Used for
  backups by Parallels
- {5FBAABE3-6958-40ff-92A7-860E329AAB41} snapshot

Without one of the snapshots above disk image is invalid.

Snapshots are read from top to bottom placing them into linear array,
which is already properly handled at the moment.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Jeff Cody <jcody@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/parallels.c | 102 +++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 77 insertions(+), 25 deletions(-)

diff --git a/block/parallels.c b/block/parallels.c
index d1b52f3..93a8498 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -42,6 +42,10 @@
 #define HEADER_VERSION 2
 #define HEADER_SIZE 64
 
+#define CURRENT_SNAP_ID "{5FBAABE3-6958-40ff-92A7-860E329AAB41}"
+#define BACKUP_SNAP_ID  "{704718E1-2314-44c8-9087-D78ED36B0F4E}"
+
+
 // always little-endian
 struct parallels_header {
     char magic[16]; // "WithoutFreeSpace"
@@ -239,13 +243,34 @@ static const char *xml_get_text(xmlNode *node, ...)
     return NULL;
 }
 
+static xmlNode *xml_find_snapshot(xmlNode *snaps, const char *guid)
+{
+    if (guid == NULL) {
+        return NULL;
+    }
+
+    for (snaps = snaps->children; snaps != NULL; snaps = snaps->next) {
+        const char *id;
+        if (snaps->type != XML_ELEMENT_NODE) {
+            continue;
+        }
+        id = xml_get_text(snaps, "GUID", NULL);
+
+        if (!xmlStrcasecmp((const xmlChar *)guid, (const xmlChar *)id)) {
+            return snaps;
+        }
+    }
+    return NULL;
+}
+
 static int parallels_open_xml(BlockDriverState *bs, int flags, Error **errp)
 {
-    int size, ret;
+    int ret, size, i;
     xmlDoc *doc = NULL;
-    xmlNode *root, *image;
+    xmlNode *root, *storage, *snaps;
     char *xml = NULL, *endptr;
     const char *data;
+    const char *leaf_snap;
     char image_path[PATH_MAX];
     Error *local_err = NULL;
     BDRVParallelsState *s = bs->opaque;
@@ -300,14 +325,47 @@ static int parallels_open_xml(BlockDriverState *bs, int flags, Error **errp)
         }
     }
 
-    image = xml_seek(root, "StorageData", "Storage", "Image", NULL);
-    data = ""; /* make gcc happy */
-    for (size = 0; image != NULL; image = image->next) {
-        if (image->type != XML_ELEMENT_NODE) {
-            continue;
+    snaps = xml_seek(root, "Snapshots", NULL);
+
+    leaf_snap = xml_get_text(snaps, "TopGUID", NULL);
+    if (leaf_snap != NULL && xml_find_snapshot(snaps, leaf_snap) == NULL) {
+        goto fail;
+    } else if (xml_find_snapshot(snaps, BACKUP_SNAP_ID) != NULL) {
+        leaf_snap = BACKUP_SNAP_ID;
+    } else if (xml_find_snapshot(snaps, CURRENT_SNAP_ID) != NULL) {
+        leaf_snap = CURRENT_SNAP_ID;
+    } else {
+        goto fail;
+    }
+
+    data = leaf_snap;
+    for (s->snaps_count = 0; data != NULL; s->snaps_count++) {
+        xmlNode *node = xml_find_snapshot(snaps, data);
+        if (node == NULL) {
+            break;
+        }
+        data = xml_get_text(node, "ParentGUID", NULL);
+    }
+    if (s->snaps_count == 0) {
+        goto fail;
+    }
+    s->snaps = g_malloc0(sizeof(ParallelsSnapshot) * s->snaps_count);
+
+    storage = xml_seek(root, "StorageData", "Storage", NULL);
+    if (storage == NULL) {
+        goto fail;
+    }
+
+    data = leaf_snap;
+    for (i = 0; i < s->snaps_count; i++) {
+        int64_t total_sectors;
+        xmlNode *image = xml_find_snapshot(storage, data);
+        xmlNode *snap = xml_find_snapshot(snaps, data);
+
+        if (image == NULL || snap == NULL) {
+            goto fail;
         }
 
-        size++;
         data = xml_get_text(image, "Type", NULL);
         if (data != NULL && strcmp(data, "Compressed")) {
             error_setg(errp, "Only compressed Parallels images are supported");
@@ -318,32 +376,26 @@ static int parallels_open_xml(BlockDriverState *bs, int flags, Error **errp)
         if (data == NULL) {
             goto fail;
         }
-    }
-    /* Images with more than 1 snapshots are not supported at the moment */
-    if (size != 1) {
-        error_setg(errp, "Parallels images with snapshots are not supported");
-        goto done;
-    }
 
-    s->snaps_count = size;
-    s->snaps = g_malloc0(sizeof(ParallelsSnapshot) * s->snaps_count);
+        path_combine(image_path, sizeof(image_path), bs->file->filename, data);
 
-    path_combine(image_path, sizeof(image_path), bs->file->filename, data);
+        ret = bdrv_open(&s->snaps[i].file, image_path, NULL, NULL,
+                        flags | BDRV_O_PROTOCOL, NULL, &local_err);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Could not open '%s': %s",
+                             image_path, error_get_pretty(local_err));
+            error_free(local_err);
+            goto done;
+        }
 
-    ret = bdrv_open(&s->snaps[0].file, image_path, NULL, NULL,
-                    flags | BDRV_O_PROTOCOL, NULL, &local_err);
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "Could not open '%s': %s",
-                         image_path, error_get_pretty(local_err));
-        error_free(local_err);
-    } else {
-        int64_t total_sectors;
         ret = parallels_open_image(s->snaps, &total_sectors, errp);
         if (bs->total_sectors != total_sectors) {
             error_setg(errp, "Invalid image: wrong total sectors");
             ret = -EINVAL;
             goto done;
         }
+
+        data = xml_get_text(snap, "ParentGUID", NULL);
     }
 
 done:
-- 
1.9.1