[Qemu-devel] [PATCH 1/3] blockdev: Add read-only option to change-blockdev

[Max Reitz]

Add an option to qmp_change_blockdev() which allows changing the
read-only status of the block device to be changed.

Some drives do not have a inherently fixed read-only status; for
instance, floppy disks can be set read-only or writable independently of
the drive. Some users may find it useful to be able to therefore change
the read-only status of a block device when changing the medium.

Signed-off-by: Max Reitz <address@hidden>
---
 blockdev.c                | 41 ++++++++++++++++++++++++++++++++++++++---
 include/sysemu/blockdev.h |  3 ++-
 qapi-schema.json          | 20 ++++++++++++++++++++
 qmp.c                     |  3 ++-
 4 files changed, 62 insertions(+), 5 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index a52f205..4140a27 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1721,7 +1721,8 @@ static void qmp_bdrv_open_encrypted(BlockDriverState *bs, 
const char *filename,
 }
 
 void qmp_change_blockdev(const char *device, const char *filename,
-                         const char *format, Error **errp)
+                         const char *format,
+                         BlockdevChangeReadOnlyMode read_only, Error **errp)
 {
     BlockBackend *blk;
     BlockDriverState *bs;
@@ -1754,10 +1755,44 @@ void qmp_change_blockdev(const char *device, const char 
*filename,
         goto out;
     }
 
-    bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
+    switch (read_only) {
+        case BLOCKDEV_CHANGE_READ_ONLY_MODE_RETAIN:
+            bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
+            break;
+
+        case BLOCKDEV_CHANGE_READ_ONLY_MODE_RO:
+            bdrv_flags = 0;
+            break;
+
+        case BLOCKDEV_CHANGE_READ_ONLY_MODE_RW:
+            bdrv_flags = BDRV_O_RDWR;
+            break;
+
+        case BLOCKDEV_CHANGE_READ_ONLY_MODE_AUTO:
+            /* try RDWR first */
+            bdrv_flags = BDRV_O_RDWR;
+            break;
+
+        default:
+            abort();
+    }
+
     bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
 
-    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, drv, NULL, errp);
+    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, drv, NULL, &err);
+
+    if (err) {
+        if (read_only == BLOCKDEV_CHANGE_READ_ONLY_MODE_AUTO) {
+            error_free(err);
+            err = NULL;
+
+            /* RDWR did not work, try RO now */
+            bdrv_flags &= ~BDRV_O_RDWR;
+            qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, drv, NULL, errp);
+        } else {
+            error_propagate(errp, err);
+        }
+    }
 
 out:
     aio_context_release(aio_context);
diff --git a/include/sysemu/blockdev.h b/include/sysemu/blockdev.h
index 09d1e30..14b4dfb 100644
--- a/include/sysemu/blockdev.h
+++ b/include/sysemu/blockdev.h
@@ -66,7 +66,8 @@ DriveInfo *drive_new(QemuOpts *arg, BlockInterfaceType 
block_default_type);
 DriveInfo *add_init_drive(const char *opts);
 
 void qmp_change_blockdev(const char *device, const char *filename,
-                         const char *format, Error **errp);
+                         const char *format,
+                         BlockdevChangeReadOnlyMode read_only, Error **errp);
 void do_commit(Monitor *mon, const QDict *qdict);
 int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
 #endif
diff --git a/qapi-schema.json b/qapi-schema.json
index d0926d9..441e001 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1543,6 +1543,26 @@
 { 'command': 'change-vnc-password', 'data': {'password': 'str'} }
 
 ##
+# @BlockdevChangeReadOnlyMode:
+#
+# Specifies the new read-only mode of a block device subject to the @change
+# command.
+#
+# @retain:  Retains the current read-only mode
+#
+# @ro:      Makes the device read-only
+#
+# @rw:      Makes the device writable
+#
+# @auto:    If the file specified can be opened with write access, the block
+#           device will be writable; otherwise it will be read-only
+#
+# Since: 2.3
+##
+{ 'enum': 'BlockdevChangeReadOnlyMode',
+  'data': ['retain', 'ro', 'rw', 'auto'] }
+
+##
 # @change:
 #
 # This command is multiple commands multiplexed together.
diff --git a/qmp.c b/qmp.c
index 0b4f131..bd63cf4 100644
--- a/qmp.c
+++ b/qmp.c
@@ -402,7 +402,8 @@ void qmp_change(const char *device, const char *target,
     if (strcmp(device, "vnc") == 0) {
         qmp_change_vnc(target, has_arg, arg, errp);
     } else {
-        qmp_change_blockdev(device, target, arg, errp);
+        qmp_change_blockdev(device, target, arg,
+                            BLOCKDEV_CHANGE_READ_ONLY_MODE_RETAIN, errp);
     }
 }
 
-- 
1.9.3