[Qemu-devel] [V5 Patch 3/4]Qemu: Command "block_set" for dynamic block params change

[Supriya Kannery]

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 parameter changes, can be 
integrated in similar lines.

Signed-off-by: Supriya Kannery <address@hidden>

---
 block.c         |   54 +++++++++++++++++++++++++++++++++++++++++++++++++
 block.h         |    2 +
 blockdev.c      |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 blockdev.h      |    1 
 hmp-commands.hx |   14 ++++++++++++
 qemu-config.c   |   13 +++++++++++
 qemu-option.c   |   25 ++++++++++++++++++++++
 qemu-option.h   |    2 +
 qmp-commands.hx |   28 +++++++++++++++++++++++++
 9 files changed, 200 insertions(+)

Index: qemu/block.c
===================================================================
--- qemu.orig/block.c
+++ qemu/block.c
@@ -651,6 +651,34 @@ unlink_and_fail:
     return ret;
 }
 
+int bdrv_reopen(BlockDriverState *bs, int bdrv_flags)
+{
+    BlockDriver *drv = bs->drv;
+    int ret = 0, open_flags;
+
+    /* Quiesce IO for the given block device */
+    qemu_aio_flush();
+    if (bdrv_flush(bs)) {
+        qerror_report(QERR_DATA_SYNC_FAILED, bs->device_name);
+        return ret;
+    }
+    open_flags = bs->open_flags;
+    bdrv_close(bs);
+
+    ret = bdrv_open(bs, bs->filename, bdrv_flags, drv);
+    if (ret < 0) {
+        /* Reopen failed. Try to open with original flags */
+        qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
+        ret = bdrv_open(bs, bs->filename, open_flags, drv);
+        if (ret < 0) {
+            /* Reopen failed with orig and modified flags */
+            abort();
+        }
+    }
+
+    return ret;
+}
+
 void bdrv_close(BlockDriverState *bs)
 {
     if (bs->drv) {
@@ -691,6 +719,32 @@ 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;
+    }
+
+    /* If no change in flags, no need to reopen */
+    if (bdrv_flags == bs->open_flags) {
+        return 0;
+    }
+
+    if (bdrv_is_inserted(bs)) {
+        /* Reopen file with changed set of flags */
+        return bdrv_reopen(bs, bdrv_flags);
+    } else {
+        /* Save hostcache change for future use */
+        bs->open_flags = bdrv_flags;
+        return 0;
+    }
+}
+
 /* 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);
@@ -97,6 +98,7 @@ 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.c
===================================================================
--- qemu.orig/blockdev.c
+++ qemu/blockdev.c
@@ -793,3 +793,64 @@ 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)
+{
+    BlockDriverState *bs = NULL;
+    QemuOpts *opts;
+    int enable;
+    const char *device, *driver;
+    int ret;
+    char usage[50];
+
+    /* Validate device */
+    device = qdict_get_str(qdict, "device");
+    bs = bdrv_find(device);
+    if (!bs) {
+        qerror_report(QERR_DEVICE_NOT_FOUND, device);
+        return -1;
+    }
+
+    opts = qemu_opts_from_qdict(qemu_find_opts("device"), qdict);
+    if (opts == NULL) {
+        return -1;
+    }
+
+    /* If input not in "param=value" format, display error */
+    driver = qemu_opt_get(opts, "driver");
+    if (driver != NULL) {
+        qerror_report(QERR_INVALID_PARAMETER, driver);
+        return -1;
+    }
+
+    /* Before validating parameters, remove "device" option */
+    ret = qemu_opt_delete(opts, "device");
+    if (ret == 1) {
+        strcpy(usage,"block_set device [prop=value][,...]");
+        qerror_report(QERR_INCORRECT_COMMAND_SYNTAX, usage);
+        return 0;
+    }
+
+    /* Validate parameters with "-drive" parameter list */
+    ret = qemu_validate_opts(opts, "drive");
+    if (ret == -1) {
+        return -1;
+    }
+
+    /* Check for 'hostcache' parameter */
+    enable = qemu_opt_get_bool(opts, "hostcache", -1);
+    if (enable != -1) {
+        return bdrv_change_hostcache(bs, enable);
+    } else {
+        qerror_report(QERR_INVALID_PARAMETER_VALUE, "hostcache","on/off");
+    }
+
+    return 0;
+
+}
+
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
Index: qemu/hmp-commands.hx
===================================================================
--- qemu.orig/hmp-commands.hx
+++ qemu/hmp-commands.hx
@@ -70,6 +70,20 @@ 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,device:O",
+        .params     = "device [prop=value][,...]",
+        .help       = "Change block device parameters [hostcache=on/off]",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_block_set,
+    },
+STEXI
address@hidden block_set @var{config}
address@hidden block_set
+Change block device parameters (eg: hostcache=on/off) while guest is running.
+ETEXI
+
 
     {
         .name       = "eject",
Index: qemu/qemu-config.c
===================================================================
--- qemu.orig/qemu-config.c
+++ qemu/qemu-config.c
@@ -517,6 +517,19 @@ QemuOptsList *qemu_find_opts(const char 
     return find_list(vm_config_groups, group);
 }
 
+/* Validate given opts list with that of defined vm_group */
+int qemu_validate_opts(QemuOpts *opts, const char *group)
+{
+    QemuOptsList *vm_group;
+
+    vm_group  = qemu_find_opts(group);
+    if (vm_group == NULL) {
+        return -1;
+    }
+
+    return qemu_opts_validate(opts, &vm_group->desc[0]);
+}
+
 void qemu_add_opts(QemuOptsList *list)
 {
     int entries, i;
Index: qemu/qemu-option.c
===================================================================
--- qemu.orig/qemu-option.c
+++ qemu/qemu-option.c
@@ -599,6 +599,31 @@ static void qemu_opt_del(QemuOpt *opt)
     qemu_free(opt);
 }
 
+/*
+ * Delete specified parameter with name "name" from opts
+ * Return
+ *     0 - Deletion Successful
+ *    -1 - Param doesn't exist in opts
+ *     1 - Deletion Successful and opts is empty.
+*/
+
+int qemu_opt_delete(QemuOpts *opts, const char *name)
+{
+    QemuOpt *opt = qemu_opt_find(opts, name);
+    if (opt == NULL) {
+        return -1;
+    }
+
+    qemu_opt_del(opt);
+
+    if ((&opts->head)->tqh_first == NULL) {
+        /* opt queue is empty */
+        return 1;
+    }
+
+    return 0;
+}
+
 int qemu_opt_set(QemuOpts *opts, const char *name, const char *value)
 {
     QemuOpt *opt;
Index: qemu/qemu-option.h
===================================================================
--- qemu.orig/qemu-option.h
+++ qemu/qemu-option.h
@@ -121,6 +121,7 @@ int qemu_opts_set(QemuOptsList *list, co
                   const char *name, const char *value);
 const char *qemu_opts_id(QemuOpts *opts);
 void qemu_opts_del(QemuOpts *opts);
+int qemu_opt_delete(QemuOpts *opts, const char *name);
 int qemu_opts_validate(QemuOpts *opts, const QemuOptDesc *desc);
 int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char 
*firstname);
 QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params, int 
permit_abbrev);
@@ -131,5 +132,6 @@ typedef int (*qemu_opts_loopfunc)(QemuOp
 int qemu_opts_print(QemuOpts *opts, void *dummy);
 int qemu_opts_foreach(QemuOptsList *list, qemu_opts_loopfunc func, void 
*opaque,
                       int abort_on_failure);
+int qemu_validate_opts(QemuOpts *opts, const char *id);
 
 #endif
Index: qemu/qmp-commands.hx
===================================================================
--- qemu.orig/qmp-commands.hx
+++ qemu/qmp-commands.hx
@@ -727,7 +727,35 @@ Example:
 
 EQMP
 
+
     {
+        .name       = "block_set",
+        .args_type  = "device:B,device:O",
+        .params     = "device [prop=value][,...]",
+        .help       = "Change block device parameters [hostcache=on/off]",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_block_set,
+    },
+
+SQMP
+block_set
+---------
+
+Change various block device parameters (eg: hostcache=on/off)
+
+Arguments:
+
+- "device": the device's ID, must be unique (json-string)
+- device parameters to be changed (eg: "hostcache": "off")
+
+Example:
+
+-> { "execute": "block_set", "arguments": { "device": "ide0-hd0", "hostcache": 
"off"} }
+<- { "return": {} }
+
+EQMP
+
+       {
         .name       = "balloon",
         .args_type  = "value:M",
         .params     = "target",