[Qemu-devel] [PATCH 13/15] qapi: introduce drive-change (v2)

[Anthony Liguori <aliguori@us.ibm.com>]

A new QMP only command to change the blockdev associated with a block device.
The semantics of change right now are just plain scary.  This command introduces
sane semantics.  For more details, see the documentation in the schema file.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
v1 -> v2
 - Rename command to drive-change (Kevin)
---
 blockdev.c       |  108 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 qapi-schema.json |   30 +++++++++++++++
 qmp-commands.hx  |    8 ++++
 3 files changed, 140 insertions(+), 6 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 07eafce..cd338ed 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -688,12 +688,101 @@ void qmp_block_passwd(const char *device, const char *password, Error **err)
     qmp_set_blockdev_password(device, password, err);
 }
 
+static void qmp_bdrv_open_encrypted(BlockDriverState *bs, const char *filename,
+                                    int bdrv_flags, BlockDriver *drv,
+                                    const char *password, Error **errp)
+{
+    if (bdrv_open(bs, filename, bdrv_flags, drv) < 0) {
+        error_set(errp, QERR_OPEN_FILE_FAILED, filename);
+        return;
+    }
+
+    if (bdrv_key_required(bs)) {
+        if (password) {
+            if (bdrv_set_key(bs, password) < 0) {
+                error_set(errp, QERR_INVALID_PASSWORD);
+            }
+        } else {
+            error_set(errp, QERR_DEVICE_ENCRYPTED, bdrv_get_device_name(bs),
+                      bdrv_get_encrypted_filename(bs));
+        }
+    } else if (password) {
+        error_set(errp, QERR_DEVICE_NOT_ENCRYPTED, bdrv_get_device_name(bs));
+    }
+}
+
+void qmp_drive_change(const char *device, const char *filename,
+                      bool has_format, const char *format,
+                      bool has_password, const char *password,
+                      Error **errp)
+{
+    BlockDriverState *bs, *bs1;
+    BlockDriver *drv = NULL;
+    int bdrv_flags;
+    Error *err = NULL;
+    bool probed_raw = false;
+
+    bs = bdrv_find(device);
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return;
+    }
+
+    if (has_format) {
+        drv = bdrv_find_whitelisted_format(format);
+        if (!drv) {
+            error_set(errp, QERR_INVALID_BLOCK_FORMAT, format);
+            return;
+        }
+    }
+
+    bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
+    bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
+
+    if (!has_password) {
+        password = NULL;
+    }
+
+    /* Try to open once with a temporary block device to make sure that
+     * the disk isn't encrypted and we lack a key.  This also helps keep
+     * this operation as a transaction.  That is, if we fail, we try very
+     * hard to make sure that the state is the same as before the operation
+     * was started.
+     */
+    bs1 = bdrv_new("");
+    qmp_bdrv_open_encrypted(bs1, filename, bdrv_flags, drv, password, &err);
+    if (!has_format && bs1->drv->unsafe_probe) {
+        probed_raw = true;
+    }
+    bdrv_delete(bs1);
+
+    if (err) {
+        error_propagate(errp, err);
+        return;
+    }
+
+    if (probed_raw) {
+        /* We will not auto probe raw files. */
+        error_set(errp, QERR_MISSING_PARAMETER, "format");
+        return;
+    }
+
+    eject_device(bs, 0, &err);
+    if (err) {
+        error_propagate(errp, err);
+        return;
+    }
+
+    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, drv, password, errp);
+}
+
 int do_change_block(Monitor *mon, const char *device,
                     const char *filename, const char *fmt)
 {
     BlockDriverState *bs;
     BlockDriver *drv = NULL;
     int bdrv_flags;
+    Error *err = NULL;
 
     bs = bdrv_find(device);
     if (!bs) {
@@ -707,16 +796,23 @@ int do_change_block(Monitor *mon, const char *device,
             return -1;
         }
     }
-    if (eject_device(bs, 0, NULL) < 0) {
-        return -1;
-    }
+
     bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
     bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
-    if (bdrv_open(bs, filename, bdrv_flags, drv) < 0) {
-        qerror_report(QERR_OPEN_FILE_FAILED, filename);
+
+    eject_device(bs, 0, &err);
+    if (err) {
+        qerror_report_err(err);
+        return -1;
+    }
+
+    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, drv, NULL, &err);
+    if (err) {
+        qerror_report_err(err);
         return -1;
     }
-    return monitor_read_bdrv_key_start(mon, bs, NULL, NULL);
+
+    return 0;
 }
 
 int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
diff --git a/qapi-schema.json b/qapi-schema.json
index 0c6c9b8..cbb5bf1 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -124,3 +124,33 @@
 #         settings may change after executing this command.
 ##
 { 'command': 'change-vnc-listen', 'data': {'target': 'str'} }
+
+##
+# @drive-change:
+#
+# This is the preferred interface for changing a block device.
+#
+# @device:   The block device name.
+#
+# @filename: The new filename for the block device.  This may contain options
+#            encoded in a format specified by @format.
+#
+# @format:   #optional The format to use open the block device
+#
+# @password: #optional The password to use if the block device is encrypted
+#
+# Returns:  Nothing on success.
+#          If @device is not a valid block device, DeviceNotFound
+#          If @format is not a valid block format, InvalidBlockFormat
+#          If @filename is encrypted and @password isn't supplied,
+#            DeviceEncrypted.  The call should be repeated with @password
+#            supplied.
+#          If @format is not specified and @filename is a format that cannot
+#            be safely probed, MissingParameter.
+#          If @filename cannot be opened, OpenFileFailed
+#
+# Since: 1.0
+##
+{ 'command': 'drive-change',
+  'data': {'device': 'str', 'filename': 'str', '*format': 'str',
+           '*password': 'str'} }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 5cab212..623f158 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -121,6 +121,14 @@ EQMP
         .mhandler.cmd_new = do_change,
     },
 
+    {
+        .name       = "drive-change",
+        .args_type  = "device:B,filename:F,format:s?password:s?",
+        .params     = "device filename [format] [password]",
+        .help       = "change a removable medium, optional format",
+        .mhandler.cmd_new = qmp_marshal_input_drive_change,
+    },
+
 SQMP
 change
 ------
-- 
1.7.4.1