[Qemu-devel] [PATCH] Fix -snapshot deleting CDROM images

[Blue Swirl]

Command line flag '-snapshot' was setting the drive flag 'snapshot'
for all drives. Therefore also CDROM devices were incorrectly marked
with BDRV_O_SNAPSHOT. Thus the backing images were accidentally deleted
at bdrv_open time, for example when changing the image with monitor
'change' command.

Fix by adding a separate 'global_snapshot' drive flag for use when the
command line flag '-snapshot' is used. Also add some extra checks
and suppress a kraxelian notation.

Signed-off-by: Blue Swirl <address@hidden>
---
 blockdev.c    |   12 +++++++++++-
 qemu-config.c |    3 +++
 vl.c          |    5 +++--
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 0a9dec3..1272a0f 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -150,7 +150,7 @@ DriveInfo *drive_init(QemuOpts *opts, int
default_to_scsi, int *fatal_error)
     int on_read_error, on_write_error;
     const char *devaddr;
     DriveInfo *dinfo;
-    int snapshot = 0;
+    int snapshot = 0, global_snapshot = 0;
     int ret;

     *fatal_error = 1;
@@ -178,6 +178,7 @@ DriveInfo *drive_init(QemuOpts *opts, int
default_to_scsi, int *fatal_error)
     secs  = qemu_opt_get_number(opts, "secs", 0);

     snapshot = qemu_opt_get_bool(opts, "snapshot", 0);
+    global_snapshot = qemu_opt_get_bool(opts, "global_snapshot", 0);
     ro = qemu_opt_get_bool(opts, "readonly", 0);

     file = qemu_opt_get(opts, "file");
@@ -268,6 +269,15 @@ DriveInfo *drive_init(QemuOpts *opts, int
default_to_scsi, int *fatal_error)
        }
     }

+    if (media == MEDIA_CDROM && snapshot) {
+        /* Can't support snapshots */
+        fprintf(stderr, "qemu: '%s' invalid media for snapshot\n", devname);
+        return NULL;
+    }
+    if (media != MEDIA_CDROM && global_snapshot) {
+        /* Can't support snapshots: ignore -snapshot for CDROMs */
+        snapshot = global_snapshot;
+    }
     if ((buf = qemu_opt_get(opts, "cache")) != NULL) {
         if (!strcmp(buf, "off") || !strcmp(buf, "none")) {
             bdrv_flags |= BDRV_O_NOCACHE;
diff --git a/qemu-config.c b/qemu-config.c
index 95abe61..e8ecec8 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -48,6 +48,9 @@ QemuOptsList qemu_drive_opts = {
             .name = "snapshot",
             .type = QEMU_OPT_BOOL,
         },{
+            .name = "global_snapshot",
+            .type = QEMU_OPT_BOOL,
+        },{
             .name = "file",
             .type = QEMU_OPT_STRING,
             .help = "disk image",
diff --git a/vl.c b/vl.c
index ba6ee11..2804855 100644
--- a/vl.c
+++ b/vl.c
@@ -646,8 +646,9 @@ static int drive_init_func(QemuOpts *opts, void *opaque)

 static int drive_enable_snapshot(QemuOpts *opts, void *opaque)
 {
-    if (NULL == qemu_opt_get(opts, "snapshot")) {
-        qemu_opt_set(opts, "snapshot", "on");
+    if (qemu_opt_get(opts, "snapshot") == NULL &&
+        qemu_opt_get(opts, "global_snapshot") == NULL) {
+        qemu_opt_set(opts, "global_snapshot", "on");
     }
     return 0;
 }
-- 
1.6.2.4