[Qemu-devel] [V2 3/3] Command "block_set" for dynamic block params change

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

New command "block_set" added for dynamically changing any of the block 
device parameters. For now, dynamic setting of hostcache params using this 
command is implemented. Other block device parameters, can be integrated 
in similar lines.

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

---
 block.c         |   41 +++++++++++++++++++++++++++++++++++++++++
 block.h         |    2 ++
 blockdev.c      |   32 ++++++++++++++++++++++++++++++++
 blockdev.h      |    1 +
 hmp-commands.hx |   15 +++++++++++++++
 qmp-commands.hx |   30 +++++++++++++++++++++++++++++-
 6 files changed, 120 insertions(+), 1 deletion(-)

Index: qemu/hmp-commands.hx
===================================================================
--- qemu.orig/hmp-commands.hx
+++ qemu/hmp-commands.hx
@@ -70,6 +70,21 @@ but should be used with extreme caution.
 resizes image files, it can not resize block devices like LVM volumes.
 ETEXI
 
+	{
+		.name       = "block_set",
+		.args_type  = "device:B,paramname:s,enable:b",
+		.params     = "device paramname enable",
+		.help       = "On/Off block device parameters like hostcache",
+		.user_print = monitor_user_noop,
+		.mhandler.cmd_new = do_block_set,
+	},
+
+STEXI
+@item block_set
+@findex block_set
+Change block device params (eg:"hostcache"=on/off) while guest is running.
+ETEXI
+
 
     {
         .name       = "eject",
Index: qemu/qmp-commands.hx
===================================================================
--- qemu.orig/qmp-commands.hx
+++ qemu/qmp-commands.hx
@@ -693,7 +693,35 @@ Example:
 
 EQMP
 
-    {
+	{
+		.name       = "block_set",
+		.args_type  = "device:B,name:s,enable:b",
+		.params     = "device name enable",
+		.help       = "Enable/Disable block device params like hostcache",
+		.user_print = monitor_user_noop,
+		.mhandler.cmd_new = do_block_set,
+	},
+
+SQMP
+block_set
+---------
+
+Change various block device parameters like hostcache.
+
+Arguments:
+
+- "device": the device's ID, must be unique (json-string)
+- "name": name of the parameter to be changed" (json-string)
+- "enable": value to be set for the parameter, 'true' or 'false' (json-bool)
+
+Example:
+
+-> { "execute": "block_set", "arguments": { "device": "ide0-hd0", "name": "hostcache", "enable": true } }
+<- { "return": {} }
+
+EQMP
+
+	{
         .name       = "balloon",
         .args_type  = "value:M",
         .params     = "target",
Index: qemu/blockdev.c
===================================================================
--- qemu.orig/blockdev.c
+++ qemu/blockdev.c
@@ -797,3 +797,35 @@ int do_block_resize(Monitor *mon, const 
 
     return 0;
 }
+
+
+/*
+ * Handle changes to block device settings, like hostcache,
+ * while guest is running.
+*/
+int do_block_set(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+	const char *device = qdict_get_str(qdict, "device");
+	const char *name = qdict_get_str(qdict, "name");
+	int enable = qdict_get_bool(qdict, "enable");
+	BlockDriverState *bs;
+
+	bs = bdrv_find(device);
+	if (!bs) {
+		qerror_report(QERR_DEVICE_NOT_FOUND, device);
+		return -1;
+	}
+
+	if (!(strcmp(name, "hostcache"))) {
+		if (bdrv_is_inserted(bs)) {
+			/* cache change applicable only if device inserted */
+			return bdrv_change_hostcache(bs, enable);
+		} else {
+			qerror_report(QERR_DEVICE_NOT_INSERTED, device);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
Index: qemu/block.c
===================================================================
--- qemu.orig/block.c
+++ qemu/block.c
@@ -651,6 +651,33 @@ unlink_and_fail:
     return ret;
 }
 
+int bdrv_reopen(BlockDriverState *bs, int bdrv_flags)
+{
+	BlockDriver *drv = bs->drv;
+	int ret = 0;
+
+	/* No need to reopen as no change in flags */
+	if (bdrv_flags == bs->open_flags)
+		return 0;
+
+	/* Quiesce IO for the given block device */
+	qemu_aio_flush();
+	bdrv_flush(bs);
+
+	bdrv_close(bs);
+	ret = bdrv_open(bs, bs->filename, bdrv_flags, drv);
+
+	/*
+	* A failed attempt to reopen the image file must lead to 'abort()'
+	*/
+	if (ret != 0) {
+		qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
+		abort();
+	}
+
+	return ret;
+}
+
 void bdrv_close(BlockDriverState *bs)
 {
     if (bs->drv) {
@@ -691,6 +718,20 @@ void bdrv_close_all(void)
     }
 }
 
+int bdrv_change_hostcache(BlockDriverState *bs, bool enable_host_cache)
+{
+	int bdrv_flags = bs->open_flags;
+
+	/* set hostcache flags (without changing WCE/flush bits) */
+	if (enable_host_cache)
+		bdrv_flags &= ~BDRV_O_NOCACHE;
+	else
+		bdrv_flags |= BDRV_O_NOCACHE;
+
+	/* Reopen file with changed set of flags */
+	return bdrv_reopen(bs, bdrv_flags);
+}
+
 /* make a BlockDriverState anonymous by removing from bdrv_state list.
    Also, NULL terminate the device_name to prevent double remove */
 void bdrv_make_anon(BlockDriverState *bs)
Index: qemu/block.h
===================================================================
--- qemu.orig/block.h
+++ qemu/block.h
@@ -71,6 +71,7 @@ void bdrv_delete(BlockDriverState *bs);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags);
 int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
               BlockDriver *drv);
+int bdrv_reopen(BlockDriverState *bs, int bdrv_flags);
 void bdrv_close(BlockDriverState *bs);
 int bdrv_attach(BlockDriverState *bs, DeviceState *qdev);
 void bdrv_detach(BlockDriverState *bs, DeviceState *qdev);
@@ -96,6 +97,7 @@ void bdrv_commit_all(void);
 int bdrv_change_backing_file(BlockDriverState *bs,
     const char *backing_file, const char *backing_fmt);
 void bdrv_register(BlockDriver *bdrv);
+int bdrv_change_hostcache(BlockDriverState *bs, bool enable_host_cache);
 
 
 typedef struct BdrvCheckResult {
Index: qemu/blockdev.h
===================================================================
--- qemu.orig/blockdev.h
+++ qemu/blockdev.h
@@ -65,5 +65,6 @@ int do_change_block(Monitor *mon, const 
 int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
 int do_snapshot_blkdev(Monitor *mon, const QDict *qdict, QObject **ret_data);
 int do_block_resize(Monitor *mon, const QDict *qdict, QObject **ret_data);
+int do_block_set(Monitor *mon, const QDict *qdict, QObject **ret_data);
 
 #endif