[Qemu-devel] [PATCH] qemu: new option for snapshot_blkdev to avoid image creation

[Federico Simoncelli]

Add the new option [-n] for snapshot_blkdev to avoid the image creation.
The file provided as [new-image-file] is considered as already initialized
and will be used after passing a check for the backing file.

Signed-off-by: Federico Simoncelli <address@hidden>
---
 blockdev.c      |   54 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 hmp-commands.hx |    7 ++++---
 qmp-commands.hx |    4 ++--
 3 files changed, 58 insertions(+), 7 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 0827bf7..bd46808 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -550,8 +550,53 @@ void do_commit(Monitor *mon, const QDict *qdict)
     }
 }
 
+static int check_snapshot_file(const char *filename, const char *oldfilename,
+                               int flags, BlockDriver *drv)
+{
+    BlockDriverState *bs;
+    char bak_filename[1024], *abs_filename;
+    int ret = 0;
+
+    bs = bdrv_new("");
+    if (!bs) {
+        return -1;
+    }
+
+    ret = bdrv_open(bs, filename, flags, drv);
+    if (ret) {
+        qerror_report(QERR_OPEN_FILE_FAILED, filename);
+        goto err0;
+    }
+
+    if (bs->backing_file) {
+        path_combine(bak_filename, sizeof(bak_filename),
+                     filename, bs->backing_file);
+
+        abs_filename = realpath(bak_filename, NULL);
+        if (!abs_filename) {
+            ret = -1;
+            goto err1;
+        }
+
+        if (strcmp(abs_filename, oldfilename)) {
+            qerror_report(QERR_OPEN_FILE_FAILED, filename);
+            ret = -1;
+        }
+
+        free(abs_filename);
+    }
+
+err1:
+    bdrv_close(bs);
+
+err0:
+    bdrv_delete(bs);
+    return ret;
+}
+
 int do_snapshot_blkdev(Monitor *mon, const QDict *qdict, QObject **ret_data)
 {
+    const int nocreate = qdict_get_try_bool(qdict, "nocreate", 0);
     const char *device = qdict_get_str(qdict, "device");
     const char *filename = qdict_get_try_str(qdict, "snapshot-file");
     const char *format = qdict_get_try_str(qdict, "format");
@@ -597,8 +642,13 @@ int do_snapshot_blkdev(Monitor *mon, const QDict *qdict, 
QObject **ret_data)
         goto out;
     }
 
-    ret = bdrv_img_create(filename, format, bs->filename,
-                          bs->drv->format_name, NULL, -1, flags);
+    if (nocreate) {
+        ret = check_snapshot_file(filename, bs->filename, flags, drv);
+    } else {
+        ret = bdrv_img_create(filename, format, bs->filename,
+                              bs->drv->format_name, NULL, -1, flags);
+    }
+
     if (ret) {
         goto out;
     }
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 9e1cca8..eb9fcd4 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -840,11 +840,12 @@ ETEXI
 
     {
         .name       = "snapshot_blkdev",
-        .args_type  = "device:B,snapshot-file:s?,format:s?",
-        .params     = "device [new-image-file] [format]",
+        .args_type  = "nocreate:-n,device:B,snapshot-file:s?,format:s?",
+        .params     = "[-n] device [new-image-file] [format]",
         .help       = "initiates a live snapshot\n\t\t\t"
                       "of device. If a new image file is specified, 
the\n\t\t\t"
-                      "new image file will become the new root image.\n\t\t\t"
+                      "new image file will be created (unless -n is\n\t\t\t"
+                      "specified) and will become the new root image.\n\t\t\t"
                       "If format is specified, the snapshot file will\n\t\t\t"
                       "be created in that format. Otherwise the\n\t\t\t"
                       "snapshot will be internal! (currently unsupported)",
diff --git a/qmp-commands.hx b/qmp-commands.hx
index d83bce5..7af36d8 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -695,8 +695,8 @@ EQMP
 
     {
         .name       = "blockdev-snapshot-sync",
-        .args_type  = "device:B,snapshot-file:s?,format:s?",
-        .params     = "device [new-image-file] [format]",
+        .args_type  = "nocreate:-n,device:B,snapshot-file:s?,format:s?",
+        .params     = "[-n] device [new-image-file] [format]",
         .user_print = monitor_user_noop,
         .mhandler.cmd_new = do_snapshot_blkdev,
     },
-- 
1.7.1