[Qemu-devel] [v2 Patch 8/9]block: Cmd "block_set_hostcache" for dynamic cache change

[Supriya Kannery <supriyak@linux.vnet.ibm.com>]

New command "block_set_hostcache" added for dynamically changing
host pagecache setting of a block device.

Usage:
 block_set_hostcache  <device> <option>
   <device> = block device
   <option> = on/off

Example:
 (qemu) block_set_hostcache ide0-hd0 off

Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>

---
Index: qemu/block.c
===================================================================
--- qemu.orig/block.c
+++ qemu/block.c
@@ -970,6 +970,30 @@ void bdrv_close_all(void)
     }
 }
 
+void bdrv_change_hostcache(BlockDriverState *bs, bool enable, Error **errp)
+{
+    int bdrv_flags = bs->open_flags;
+
+    /* set hostcache flags (without changing WCE/flush bits) */
+    if (enable) {
+        bdrv_flags &= ~BDRV_O_NOCACHE;
+    } else {
+        bdrv_flags |= BDRV_O_NOCACHE;
+    }
+
+    /* If no change in flags, no need to reopen */
+    if (bdrv_flags != bs->open_flags) {
+        if (bdrv_is_inserted(bs)) {
+            /* Reopen file with changed set of flags */
+            bdrv_flags &= ~BDRV_O_CACHE_WB;
+            bdrv_reopen(bs, bdrv_flags, errp);
+        } else {
+            /* Save hostcache change for future use */
+            bs->open_flags = bdrv_flags;
+        }
+    }
+}
+
 /*
  * Wait for pending requests to complete across all BlockDriverStates
  *
Index: qemu/blockdev.c
===================================================================
--- qemu.orig/blockdev.c
+++ qemu/blockdev.c
@@ -1191,3 +1191,22 @@ BlockJobInfoList *qmp_query_block_jobs(E
     bdrv_iterate(do_qmp_query_block_jobs_one, &prev);
     return dummy.next;
 }
+
+/*
+ * Change host page cache setting while guest is running.
+*/
+void qmp_block_set_hostcache(const char *device, bool enable,
+                             Error **errp)
+{
+    BlockDriverState *bs = NULL;
+
+    /* Validate device */
+    bs = bdrv_find(device);
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return;
+    }
+
+    bdrv_change_hostcache(bs, enable, errp);
+    return;
+}
Index: qemu/hmp-commands.hx
===================================================================
--- qemu.orig/hmp-commands.hx
+++ qemu/hmp-commands.hx
@@ -1344,6 +1344,21 @@ passed since 1970, i.e. unix epoch.
 ETEXI
 
     {
+        .name       = "block_set_hostcache",
+        .args_type  = "device:B,option:b",
+        .params     = "device on|off",
+        .help       = "Change setting of host pagecache",
+        .mhandler.cmd = hmp_block_set_hostcache,
+    },
+
+STEXI
+@item block_set_hostcache @var{device} @var{option}
+@findex block_set_hostcache
+Change host pagecache setting of a block device while guest is running.
+ETEXI
+
+
+    {
         .name       = "info",
         .args_type  = "item:s?",
         .params     = "[subcommand]",
Index: qemu/qmp-commands.hx
===================================================================
--- qemu.orig/qmp-commands.hx
+++ qemu/qmp-commands.hx
@@ -987,6 +987,30 @@ Example:
 EQMP
 
     {
+        .name       = "block_set_hostcache",
+        .args_type  = "device:B,option:b",
+        .mhandler.cmd_new = qmp_marshal_input_block_set_hostcache,
+    },
+
+SQMP
+block_set_hostcache
+-------------------
+
+Change host pagecache setting of a block device
+
+Arguments:
+
+- "device": the device's ID, must be unique (json-string)
+- "option": hostcache setting (json-bool)
+
+Example:
+-> { +"execute": "block_set_hostcache", "arguments": { "device": "ide0-hd0", "option": false } }
+<- { "return": {} }
+
+EQMP
+
+
+    {
         .name       = "set_password",
         .args_type  = "protocol:s,password:s,connected:s?",
         .mhandler.cmd_new = qmp_marshal_input_set_password,
Index: qemu/qapi-schema.json
===================================================================
--- qemu.orig/qapi-schema.json
+++ qemu/qapi-schema.json
@@ -1604,6 +1604,23 @@
             'iops': 'int', 'iops_rd': 'int', 'iops_wr': 'int' } }
 
 ##
+# @block_set_hostcache:
+#
+# Change host pagecache setting of a block device
+#
+# @device: name of the block device
+#
+# @option: hostcache setting (true/false)
+#
+# Returns: Nothing on success
+#          If @device is not a valid block device, DeviceNotFound
+#
+# Since: 1.2
+##
+{ 'command': 'block_set_hostcache',
+  'data': { 'device': 'str', 'option': 'bool' } }
+
+##
 # @block-stream:
 #
 # Copy data from a backing file into a block device.
Index: qemu/hmp.c
===================================================================
--- qemu.orig/hmp.c
+++ qemu/hmp.c
@@ -837,6 +837,15 @@ void hmp_block_set_io_throttle(Monitor *
     hmp_handle_error(mon, &err);
 }
 
+void hmp_block_set_hostcache(Monitor *mon, const QDict *qdict)
+{
+    Error *err = NULL;
+
+    qmp_block_set_hostcache(qdict_get_str(qdict, "device"),
+                              qdict_get_bool(qdict, "option"), &err);
+    hmp_handle_error(mon, &err);
+}
+
 void hmp_block_stream(Monitor *mon, const QDict *qdict)
 {
     Error *error = NULL;
Index: qemu/hmp.h
===================================================================
--- qemu.orig/hmp.h
+++ qemu/hmp.h
@@ -66,5 +66,6 @@ void hmp_netdev_add(Monitor *mon, const 
 void hmp_netdev_del(Monitor *mon, const QDict *qdict);
 void hmp_getfd(Monitor *mon, const QDict *qdict);
 void hmp_closefd(Monitor *mon, const QDict *qdict);
+void hmp_block_set_hostcache(Monitor *mon, const QDict *qdict);
 
 #endif
Index: qemu/block.h
===================================================================
--- qemu.orig/block.h
+++ qemu/block.h
@@ -187,6 +187,7 @@ int bdrv_commit_all(void);
 int bdrv_change_backing_file(BlockDriverState *bs,
     const char *backing_file, const char *backing_fmt);
 void bdrv_register(BlockDriver *bdrv);
+void bdrv_change_hostcache(BlockDriverState *bs, bool enable, Error **errp);
 
 
 typedef struct BdrvCheckResult {