[Qemu-devel] [PATCH] Copy snapshots out of QCOW2 disk

[disheng . su]

From: edison <address@hidden>

In order to backup snapshots, created from QCOW2 iamge, we want to copy 
snapshots out of QCOW2 disk to a seperate storage.
The following patch adds a new option in "qemu-img": qemu-img convert -f qcow2 
-O qcow2 -s snapshot_name src_img bck_img.
Right now, it only supports to copy the full snapshot, delta snapshot is on the 
way.

Signed-off-by: Disheng Su <address@hidden>
---
 block.c                |   11 +++++++++++
 block.h                |    2 ++
 block/qcow2-snapshot.c |   26 ++++++++++++++++++++++++++
 block/qcow2.c          |    1 +
 block/qcow2.h          |    1 +
 block_int.h            |    2 ++
 qemu-img-cmds.hx       |    4 ++--
 qemu-img.c             |   19 ++++++++++++++++++-
 8 files changed, 63 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index ebbc376..eaf78f6 100644
--- a/block.c
+++ b/block.c
@@ -1899,6 +1899,17 @@ int bdrv_snapshot_list(BlockDriverState *bs,
     return -ENOTSUP;
 }
 
+int bdrv_snapshot_load(BlockDriverState *bs,
+                      const char *snapshot_name)
+{
+    BlockDriver *drv = bs->drv;
+    if (!drv)
+        return -ENOMEDIUM;
+    if (drv->bdrv_snapshot_load)
+       return drv->bdrv_snapshot_load(bs, snapshot_name);
+    return -ENOTSUP;
+}
+
 #define NB_SUFFIXES 4
 
 char *get_human_readable_size(char *buf, int buf_size, int64_t size)
diff --git a/block.h b/block.h
index 5f64380..9ec6219 100644
--- a/block.h
+++ b/block.h
@@ -211,6 +211,8 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
 int bdrv_snapshot_delete(BlockDriverState *bs, const char *snapshot_id);
 int bdrv_snapshot_list(BlockDriverState *bs,
                        QEMUSnapshotInfo **psn_info);
+int bdrv_snapshot_load(BlockDriverState *bs,
+                       const char *snapshot_name);
 char *bdrv_snapshot_dump(char *buf, int buf_size, QEMUSnapshotInfo *sn);
 
 char *get_human_readable_size(char *buf, int buf_size, int64_t size);
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 6228612..e663e8b 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -416,3 +416,29 @@ int qcow2_snapshot_list(BlockDriverState *bs, 
QEMUSnapshotInfo **psn_tab)
     return s->nb_snapshots;
 }
 
+int qcow2_snapshot_load(BlockDriverState *bs, const char *snapshot_name) {
+    int i, snapshot_index, l1_size2;
+    BDRVQcowState *s = bs->opaque;
+    QCowSnapshot *sn;
+    snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_name);
+    if (snapshot_index < 0)
+        return -ENOENT;
+    sn = &s->snapshots[snapshot_index];
+    s->l1_size = sn->l1_size;
+    l1_size2 = s->l1_size * sizeof(uint64_t);
+    if (s->l1_table != NULL) {
+       qemu_free(s->l1_table);
+    }
+    s->l1_table_offset = sn->l1_table_offset;
+    s->l1_table = qemu_mallocz(
+            align_offset(l1_size2, 512));
+    /* copy the snapshot l1 table to the current l1 table */
+    if (bdrv_pread(bs->file, sn->l1_table_offset,
+                   s->l1_table, l1_size2) != l1_size2) {
+        return -1;
+    }
+    for(i = 0;i < s->l1_size; i++) {
+        be64_to_cpus(&s->l1_table[i]);
+    }
+    return 0;
+}
diff --git a/block/qcow2.c b/block/qcow2.c
index a53014d..da98a01 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1352,6 +1352,7 @@ static BlockDriver bdrv_qcow2 = {
     .bdrv_snapshot_goto     = qcow2_snapshot_goto,
     .bdrv_snapshot_delete   = qcow2_snapshot_delete,
     .bdrv_snapshot_list     = qcow2_snapshot_list,
+    .bdrv_snapshot_load     = qcow2_snapshot_load,
     .bdrv_get_info     = qcow_get_info,
 
     .bdrv_save_vmstate    = qcow_save_vmstate,
diff --git a/block/qcow2.h b/block/qcow2.h
index 3ff162e..cbbba48 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -211,6 +211,7 @@ int qcow2_snapshot_create(BlockDriverState *bs, 
QEMUSnapshotInfo *sn_info);
 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id);
 int qcow2_snapshot_delete(BlockDriverState *bs, const char *snapshot_id);
 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab);
+int qcow2_snapshot_load(BlockDriverState *bs, const char *snapshot_name);
 
 void qcow2_free_snapshots(BlockDriverState *bs);
 int qcow2_read_snapshots(BlockDriverState *bs);
diff --git a/block_int.h b/block_int.h
index e8e7156..93d5a1b 100644
--- a/block_int.h
+++ b/block_int.h
@@ -93,6 +93,8 @@ struct BlockDriver {
     int (*bdrv_snapshot_delete)(BlockDriverState *bs, const char *snapshot_id);
     int (*bdrv_snapshot_list)(BlockDriverState *bs,
                               QEMUSnapshotInfo **psn_info);
+    int (*bdrv_snapshot_load)(BlockDriverState *bs,
+                              const char *snapshot_name);
     int (*bdrv_get_info)(BlockDriverState *bs, BlockDriverInfo *bdi);
 
     int (*bdrv_save_vmstate)(BlockDriverState *bs, const uint8_t *buf,
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 6d3e5f8..6c7176f 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -28,9 +28,9 @@ STEXI
 ETEXI
 
 DEF("convert", img_convert,
-    "convert [-c] [-f fmt] [-O output_fmt] [-o options] filename [filename2 
[...]] output_filename")
+    "convert [-c] [-f fmt] [-O output_fmt] [-o options] [-s snapshot_name] 
filename [filename2 [...]] output_filename")
 STEXI
address@hidden convert [-c] [-f @var{fmt}] [-O @var{output_fmt}] [-o 
@var{options}] @var{filename} address@hidden [...]] @var{output_filename}
address@hidden convert [-c] [-f @var{fmt}] [-O @var{output_fmt}] [-o 
@var{options}] [-s @var{snapshot_name}] @var{filename} address@hidden [...]] 
@var{output_filename}
 ETEXI
 
 DEF("info", img_info,
diff --git a/qemu-img.c b/qemu-img.c
index 4e035e4..7ff015d 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -646,13 +646,14 @@ static int img_convert(int argc, char **argv)
     BlockDriverInfo bdi;
     QEMUOptionParameter *param = NULL, *create_options = NULL;
     char *options = NULL;
+    const char *snapshot_name = NULL;
 
     fmt = NULL;
     out_fmt = "raw";
     out_baseimg = NULL;
     flags = 0;
     for(;;) {
-        c = getopt(argc, argv, "f:O:B:hce6o:");
+        c = getopt(argc, argv, "f:O:B:s:hce6o:");
         if (c == -1)
             break;
         switch(c) {
@@ -680,6 +681,9 @@ static int img_convert(int argc, char **argv)
         case 'o':
             options = optarg;
             break;
+        case 's':
+            snapshot_name = optarg;
+            break;
         }
     }
 
@@ -711,6 +715,19 @@ static int img_convert(int argc, char **argv)
         total_sectors += bs_sectors;
     }
 
+    if (snapshot_name != NULL) {
+       if (bs_n > 1) {
+            error("No support for concatenating multiple snapshot\n");
+            ret = -1;
+            goto out;
+       }
+       if (bdrv_snapshot_load(bs[0], snapshot_name) < 0) {
+            error("Failed to load snapshot\n");
+            ret = -1;
+            goto out;
+       }
+    }
+
     /* Find driver and parse its options */
     drv = bdrv_find_format(out_fmt);
     if (!drv) {
-- 
1.7.2.2