[Qemu-devel] [PATCH v4 35/38] blockdev: read-only-mode for blockdev-change-medium

[Max Reitz <mreitz@redhat.com>]

Add an option to qmp_blockdev_change_medium() which allows changing the
read-only status of the block device whose medium is 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 <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 blockdev.c           | 25 ++++++++++++++++++++++++-
 hmp.c                |  2 +-
 qapi/block-core.json | 24 +++++++++++++++++++++++-
 qmp-commands.hx      | 24 +++++++++++++++++++++++-
 qmp.c                |  3 ++-
 5 files changed, 73 insertions(+), 5 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 0f18c92..77e47da 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2104,6 +2104,8 @@ void qmp_blockdev_insert_medium(const char *device, const char *node_name,
 
 void qmp_blockdev_change_medium(const char *device, const char *filename,
                                 bool has_format, const char *format,
+                                bool has_read_only,
+                                BlockdevChangeReadOnlyMode read_only,
                                 Error **errp)
 {
     BlockBackend *blk;
@@ -2125,7 +2127,28 @@ void qmp_blockdev_change_medium(const char *device, const char *filename,
     }
 
     blk_rs = blk_get_root_state(blk);
-    bdrv_flags = blk_rs->read_only ? 0 : BDRV_O_RDWR;
+
+    if (!has_read_only) {
+        read_only = BLOCKDEV_CHANGE_READ_ONLY_MODE_RETAIN;
+    }
+
+    switch (read_only) {
+    case BLOCKDEV_CHANGE_READ_ONLY_MODE_RETAIN:
+        bdrv_flags = blk_rs->read_only ? 0 : BDRV_O_RDWR;
+        break;
+
+    case BLOCKDEV_CHANGE_READ_ONLY_MODE_READ_ONLY:
+        bdrv_flags = 0;
+        break;
+
+    case BLOCKDEV_CHANGE_READ_ONLY_MODE_READ_WRITE:
+        bdrv_flags = BDRV_O_RDWR;
+        break;
+
+    default:
+        abort();
+    }
+
     bdrv_flags |= blk_rs->open_flags & ~BDRV_O_RDWR;
 
     if (has_format) {
diff --git a/hmp.c b/hmp.c
index 1a201a9..a4f3634 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1327,7 +1327,7 @@ void hmp_change(Monitor *mon, const QDict *qdict)
         }
         qmp_change("vnc", target, !!arg, arg, &err);
     } else {
-        qmp_blockdev_change_medium(device, target, !!arg, arg, &err);
+        qmp_blockdev_change_medium(device, target, !!arg, arg, false, 0, &err);
         if (err &&
             error_get_class(err) == ERROR_CLASS_DEVICE_ENCRYPTED) {
             error_free(err);
diff --git a/qapi/block-core.json b/qapi/block-core.json
index bc56625..cb99cad 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1944,6 +1944,24 @@
 
 
 ##
+# @BlockdevChangeReadOnlyMode:
+#
+# Specifies the new read-only mode of a block device subject to the
+# @blockdev-change-medium command.
+#
+# @retain:      Retains the current read-only mode
+#
+# @read-only:   Makes the device read-only
+#
+# @read-write:  Makes the device writable
+#
+# Since: 2.3
+##
+{ 'enum': 'BlockdevChangeReadOnlyMode',
+  'data': ['retain', 'read-only', 'read-write'] }
+
+
+##
 # @blockdev-change-medium:
 #
 # Changes the medium inserted into a block device by ejecting the current medium
@@ -1958,12 +1976,16 @@
 # @format:          #optional, format to open the new image with (defaults to
 #                   the probed format)
 #
+# @read-only-mode:  #optional, change the read-only mode of the device; defaults
+#                   to 'retain'
+#
 # Since: 2.5
 ##
 { 'command': 'blockdev-change-medium',
   'data': { 'device': 'str',
             'filename': 'str',
-            '*format': 'str' } }
+            '*format': 'str',
+            '*read-only-mode': 'BlockdevChangeReadOnlyMode' } }
 
 
 ##
diff --git a/qmp-commands.hx b/qmp-commands.hx
index ce8516b..5936b24 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -4091,7 +4091,7 @@ EQMP
 
     {
         .name       = "blockdev-change-medium",
-        .args_type  = "device:B,filename:F,format:s?",
+        .args_type  = "device:B,filename:F,format:s?,read-only-mode:s?",
         .mhandler.cmd_new = qmp_marshal_input_blockdev_change_medium,
     },
 
@@ -4107,6 +4107,8 @@ Arguments:
 - "device": device name (json-string)
 - "filename": filename of the new image (json-string)
 - "format": format of the new image (json-string, optional)
+- "read-only-mode": new read-only mode (json-string, optional)
+          - Possible values: "retain" (default), "read-only", "read-write"
 
 Examples:
 
@@ -4118,6 +4120,26 @@ Examples:
                             "format": "raw" } }
 <- { "return": {} }
 
+2. Load a read-only medium into a writable drive
+
+-> { "execute": "blockdev-change-medium",
+             "arguments": { "device": "isa-fd0",
+                            "filename": "/srv/images/ro.img",
+                            "format": "raw",
+                            "read-only-mode": "retain" } }
+
+<- { "error":
+     { "class": "GenericError",
+       "desc": "Could not open '/srv/images/ro.img': Permission denied" } }
+
+-> { "execute": "blockdev-change-medium",
+             "arguments": { "device": "isa-fd0",
+                            "filename": "/srv/images/ro.img",
+                            "format": "raw",
+                            "read-only-mode": "read-only" } }
+
+<- { "return": {} }
+
 EQMP
 
     {
diff --git a/qmp.c b/qmp.c
index 55f006c..3493b3b 100644
--- a/qmp.c
+++ b/qmp.c
@@ -413,7 +413,8 @@ void qmp_change(const char *device, const char *target,
     if (strcmp(device, "vnc") == 0) {
         qmp_change_vnc(target, has_arg, arg, errp);
     } else {
-        qmp_blockdev_change_medium(device, target, has_arg, arg, errp);
+        qmp_blockdev_change_medium(device, target, has_arg, arg, false, 0,
+                                   errp);
     }
 }
 
-- 
2.4.6