Patchwork [2/3] QAPI: Introduce memchar-write QMP command

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Submitter Lei Li
Date Jan. 22, 2013, 8:12 a.m.
Message ID <1358842372-16344-3-git-send-email-lilei@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/214459/
State New
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Comments

Lei Li - Jan. 22, 2013, 8:12 a.m.
Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 hmp-commands.hx  |   16 ++++++++++++++++
 hmp.c            |   13 +++++++++++++
 hmp.h            |    1 +
 qapi-schema.json |   41 +++++++++++++++++++++++++++++++++++++++++
 qemu-char.c      |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
 6 files changed, 153 insertions(+), 0 deletions(-)
Luiz Capitulino - Jan. 22, 2013, 4:27 p.m.
On Tue, 22 Jan 2013 16:12:51 +0800
Lei Li <lilei@linux.vnet.ibm.com> wrote:

> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> ---
>  hmp-commands.hx  |   16 ++++++++++++++++
>  hmp.c            |   13 +++++++++++++
>  hmp.h            |    1 +
>  qapi-schema.json |   41 +++++++++++++++++++++++++++++++++++++++++
>  qemu-char.c      |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
>  6 files changed, 153 insertions(+), 0 deletions(-)
> 
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 0934b9b..e546c76 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -837,6 +837,22 @@ STEXI
>  @item nmi @var{cpu}
>  @findex nmi
>  Inject an NMI on the given CPU (x86 only).
> +
> +ETEXI
> +
> +    {
> +        .name       = "memchar_write",
> +        .args_type  = "chardev:s,data:s",
> +        .params     = "chardev data",

This is missing .help. Please look at the other entries for examples.

> +        .mhandler.cmd = hmp_memchar_write,
> +    },
> +
> +STEXI
> +@item memchar_write @var{chardev} @var{data}
> +@findex memchar_write
> +Provide writing interface for CirMemCharDriver. Write @var{data}
> +to char device 'memory'.
> +
>  ETEXI
>  
>      {
> diff --git a/hmp.c b/hmp.c
> index c7b6ba0..546d687 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -684,6 +684,19 @@ void hmp_pmemsave(Monitor *mon, const QDict *qdict)
>      hmp_handle_error(mon, &errp);
>  }
>  
> +void hmp_memchar_write(Monitor *mon, const QDict *qdict)
> +{
> +    uint32_t size;
> +    const char *chardev = qdict_get_str(qdict, "chardev");
> +    const char *data = qdict_get_str(qdict, "data");
> +    Error *errp = NULL;
> +
> +    size = strlen(data);
> +    qmp_memchar_write(chardev, size, data, false, 0, &errp);
> +
> +    hmp_handle_error(mon, &errp);
> +}
> +
>  static void hmp_cont_cb(void *opaque, int err)
>  {
>      if (!err) {
> diff --git a/hmp.h b/hmp.h
> index 44be683..06d6ea2 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -43,6 +43,7 @@ void hmp_system_powerdown(Monitor *mon, const QDict *qdict);
>  void hmp_cpu(Monitor *mon, const QDict *qdict);
>  void hmp_memsave(Monitor *mon, const QDict *qdict);
>  void hmp_pmemsave(Monitor *mon, const QDict *qdict);
> +void hmp_memchar_write(Monitor *mon, const QDict *qdict);
>  void hmp_cont(Monitor *mon, const QDict *qdict);
>  void hmp_system_wakeup(Monitor *mon, const QDict *qdict);
>  void hmp_inject_nmi(Monitor *mon, const QDict *qdict);
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 6d7252b..c34e9ac 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -325,6 +325,47 @@
>  { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
>  
>  ##
> +# @DataFormat:
> +#
> +# An enumeration of data format.
> +#
> +# @utf8: The data format is 'utf8'.
> +#
> +# @base64: The data format is 'base64'.
> +#
> +# Since: 1.4
> +##
> +{ 'enum': 'DataFormat'
> +  'data': [ 'utf8', 'base64' ] }
> +
> +##
> +# @memchar-write:
> +#
> +# Provide writing interface for memchardev. Write data to char
> +# device 'memory'.
> +#
> +# @chardev: the name of the memory char device.

I wonder if this should be 'device' instead.

> +#
> +# @size: the size to write in bytes.
> +#
> +# @data: the source data write to memchar.
> +#
> +# @format: #optional the format of the data write to chardev 'memory',
> +#          by default is 'utf8'.
> +#
> +# Returns: Nothing on success
> +#          If @chardev is not a valid char device, DeviceNotFound
> +#
> +# Notes: For now assume 'drop' behaver, which would result in writes
> +#        dropping queued data.

I agree this is the desired interface, but it's not what it does, see
below.

> +#
> +# Since: 1.4
> +##
> +{ 'command': 'memchar-write',
> +  'data': {'chardev': 'str', 'size': 'int', 'data': 'str',
> +           '*format': 'DataFormat'} }
> +
> +##
>  # @CommandInfo:
>  #
>  # Information about a QMP command
> diff --git a/qemu-char.c b/qemu-char.c
> index b323e94..c3bb6ec 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -2754,6 +2754,54 @@ fail:
>      return NULL;
>  }
>  
> +static bool qemu_is_chr(const CharDriverState *chr, const char *filename)
> +{
> +    return strcmp(chr->filename, filename);
> +}
> +
> +void qmp_memchar_write(const char *chardev, int64_t size,
> +                       const char *data, bool has_format,
> +                       enum DataFormat format,
> +                       Error **errp)
> +{
> +    CharDriverState *chr;
> +    guchar *write_data;
> +    int ret;
> +    gsize write_count;
> +
> +    chr = qemu_chr_find(chardev);
> +    if (!chr) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, chardev);
> +        return;
> +    }
> +
> +    if (qemu_is_chr(chr, "memory")) {
> +        error_setg(errp,"%s is not memory char device\n", chardev);

Please, drop the trailing '\n'.

> +        return;
> +    }
> +
> +    /* XXX: Drop the coming data when the buffer is full. */
> +    if (cirmem_chr_is_full(chr)) {
> +        error_setg(errp, "Memory device %s is full", chardev);
> +        return;
> +    }

This is where the code contradicts the doc, and we can't fix this
later because we'd change the interface.

Why can't you just drop this check?

> +
> +    write_count = (gsize)size;
> +
> +    if (has_format && (format == DATA_FORMAT_BASE64)) {
> +        write_data = g_base64_decode(data, &write_count);
> +    } else {
> +        write_data = (uint8_t *)data;
> +    }
> +
> +    ret = cirmem_chr_write(chr, write_data, write_count);
> +
> +    if (ret < 0) {
> +        error_setg(errp, "Failed to write to device %s", chardev);
> +        return;
> +    }
> +}
> +
>  QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
>  {
>      char host[65], port[33], width[8], height[8];
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index cbf1280..8ad06d0 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -466,6 +466,40 @@ Note: inject-nmi fails when the guest doesn't support injecting.
>  EQMP
>  
>      {
> +        .name       = "memchar-write",
> +        .args_type  = "chardev:s,size:i,data:s,format:s?",
> +        .help       = "write size of data to memory chardev",

Please, drop .help. We only use it for hmp commands.

> +        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
> +    },
> +
> +SQMP
> +memchar-write
> +-------------
> +
> +Provide writing interface for CirMemCharDriver. Write data to memory
> +char device.
> +
> +Arguments:
> +
> +- "chardev": the name of the char device, must be unique (json-string)
> +- "size": the memory size, in bytes, should be power of 2 (json-int)
> +- "data": the source data write to memory (json-string)
> +- "format": the data format write to memory, default is
> +            utf8. (json-string, optional)
> +          - Possible values: "utf8", "base64"
> +
> +Example:
> +
> +-> { "execute": "memchar-write",
> +                "arguments": { "chardev": foo,
> +                               "size": 8,
> +                               "data": "abcdefgh",
> +                               "format": "utf8" } }
> +<- { "return": {} }
> +
> +EQMP
> +
> +    {
>          .name       = "xen-save-devices-state",
>          .args_type  = "filename:F",
>      .mhandler.cmd_new = qmp_marshal_input_xen_save_devices_state,
Lei Li - Jan. 23, 2013, 3:30 a.m.
On 01/23/2013 12:27 AM, Luiz Capitulino wrote:
> On Tue, 22 Jan 2013 16:12:51 +0800
> Lei Li <lilei@linux.vnet.ibm.com> wrote:
>
>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>> ---
>>   hmp-commands.hx  |   16 ++++++++++++++++
>>   hmp.c            |   13 +++++++++++++
>>   hmp.h            |    1 +
>>   qapi-schema.json |   41 +++++++++++++++++++++++++++++++++++++++++
>>   qemu-char.c      |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>>   qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
>>   6 files changed, 153 insertions(+), 0 deletions(-)
>>
>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>> index 0934b9b..e546c76 100644
>> --- a/hmp-commands.hx
>> +++ b/hmp-commands.hx
>> @@ -837,6 +837,22 @@ STEXI
>>   @item nmi @var{cpu}
>>   @findex nmi
>>   Inject an NMI on the given CPU (x86 only).
>> +
>> +ETEXI
>> +
>> +    {
>> +        .name       = "memchar_write",
>> +        .args_type  = "chardev:s,data:s",
>> +        .params     = "chardev data",
> This is missing .help. Please look at the other entries for examples.

Hmm, I did add .help here before version 5, and I get rid of them
based on your comments "Help doesn't make sense for HMP."...
So I guess it's misunderstanding here?

>
>> +        .mhandler.cmd = hmp_memchar_write,
>> +    },
>> +
>> +STEXI
>> +@item memchar_write @var{chardev} @var{data}
>> +@findex memchar_write
>> +Provide writing interface for CirMemCharDriver. Write @var{data}
>> +to char device 'memory'.
>> +
>>   ETEXI
>>   
>>       {
>> diff --git a/hmp.c b/hmp.c
>> index c7b6ba0..546d687 100644
>> --- a/hmp.c
>> +++ b/hmp.c
>> @@ -684,6 +684,19 @@ void hmp_pmemsave(Monitor *mon, const QDict *qdict)
>>       hmp_handle_error(mon, &errp);
>>   }
>>   
>> +void hmp_memchar_write(Monitor *mon, const QDict *qdict)
>> +{
>> +    uint32_t size;
>> +    const char *chardev = qdict_get_str(qdict, "chardev");
>> +    const char *data = qdict_get_str(qdict, "data");
>> +    Error *errp = NULL;
>> +
>> +    size = strlen(data);
>> +    qmp_memchar_write(chardev, size, data, false, 0, &errp);
>> +
>> +    hmp_handle_error(mon, &errp);
>> +}
>> +
>>   static void hmp_cont_cb(void *opaque, int err)
>>   {
>>       if (!err) {
>> diff --git a/hmp.h b/hmp.h
>> index 44be683..06d6ea2 100644
>> --- a/hmp.h
>> +++ b/hmp.h
>> @@ -43,6 +43,7 @@ void hmp_system_powerdown(Monitor *mon, const QDict *qdict);
>>   void hmp_cpu(Monitor *mon, const QDict *qdict);
>>   void hmp_memsave(Monitor *mon, const QDict *qdict);
>>   void hmp_pmemsave(Monitor *mon, const QDict *qdict);
>> +void hmp_memchar_write(Monitor *mon, const QDict *qdict);
>>   void hmp_cont(Monitor *mon, const QDict *qdict);
>>   void hmp_system_wakeup(Monitor *mon, const QDict *qdict);
>>   void hmp_inject_nmi(Monitor *mon, const QDict *qdict);
>> diff --git a/qapi-schema.json b/qapi-schema.json
>> index 6d7252b..c34e9ac 100644
>> --- a/qapi-schema.json
>> +++ b/qapi-schema.json
>> @@ -325,6 +325,47 @@
>>   { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
>>   
>>   ##
>> +# @DataFormat:
>> +#
>> +# An enumeration of data format.
>> +#
>> +# @utf8: The data format is 'utf8'.
>> +#
>> +# @base64: The data format is 'base64'.
>> +#
>> +# Since: 1.4
>> +##
>> +{ 'enum': 'DataFormat'
>> +  'data': [ 'utf8', 'base64' ] }
>> +
>> +##
>> +# @memchar-write:
>> +#
>> +# Provide writing interface for memchardev. Write data to char
>> +# device 'memory'.
>> +#
>> +# @chardev: the name of the memory char device.
> I wonder if this should be 'device' instead.

ok.

>> +#
>> +# @size: the size to write in bytes.
>> +#
>> +# @data: the source data write to memchar.
>> +#
>> +# @format: #optional the format of the data write to chardev 'memory',
>> +#          by default is 'utf8'.
>> +#
>> +# Returns: Nothing on success
>> +#          If @chardev is not a valid char device, DeviceNotFound
>> +#
>> +# Notes: For now assume 'drop' behaver, which would result in writes
>> +#        dropping queued data.
> I agree this is the desired interface, but it's not what it does, see
> below.
>
>> +#
>> +# Since: 1.4
>> +##
>> +{ 'command': 'memchar-write',
>> +  'data': {'chardev': 'str', 'size': 'int', 'data': 'str',
>> +           '*format': 'DataFormat'} }
>> +
>> +##
>>   # @CommandInfo:
>>   #
>>   # Information about a QMP command
>> diff --git a/qemu-char.c b/qemu-char.c
>> index b323e94..c3bb6ec 100644
>> --- a/qemu-char.c
>> +++ b/qemu-char.c
>> @@ -2754,6 +2754,54 @@ fail:
>>       return NULL;
>>   }
>>   
>> +static bool qemu_is_chr(const CharDriverState *chr, const char *filename)
>> +{
>> +    return strcmp(chr->filename, filename);
>> +}
>> +
>> +void qmp_memchar_write(const char *chardev, int64_t size,
>> +                       const char *data, bool has_format,
>> +                       enum DataFormat format,
>> +                       Error **errp)
>> +{
>> +    CharDriverState *chr;
>> +    guchar *write_data;
>> +    int ret;
>> +    gsize write_count;
>> +
>> +    chr = qemu_chr_find(chardev);
>> +    if (!chr) {
>> +        error_set(errp, QERR_DEVICE_NOT_FOUND, chardev);
>> +        return;
>> +    }
>> +
>> +    if (qemu_is_chr(chr, "memory")) {
>> +        error_setg(errp,"%s is not memory char device\n", chardev);
> Please, drop the trailing '\n'.
>
Ah, sorry for this..

>> +        return;
>> +    }
>> +
>> +    /* XXX: Drop the coming data when the buffer is full. */
>> +    if (cirmem_chr_is_full(chr)) {
>> +        error_setg(errp, "Memory device %s is full", chardev);
>> +        return;
>> +    }
> This is where the code contradicts the doc, and we can't fix this
> later because we'd change the interface.
>
> Why can't you just drop this check?
>
>> +
>> +    write_count = (gsize)size;
>> +
>> +    if (has_format && (format == DATA_FORMAT_BASE64)) {
>> +        write_data = g_base64_decode(data, &write_count);
>> +    } else {
>> +        write_data = (uint8_t *)data;
>> +    }
>> +
>> +    ret = cirmem_chr_write(chr, write_data, write_count);
>> +
>> +    if (ret < 0) {
>> +        error_setg(errp, "Failed to write to device %s", chardev);
>> +        return;
>> +    }
>> +}
>> +
>>   QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
>>   {
>>       char host[65], port[33], width[8], height[8];
>> diff --git a/qmp-commands.hx b/qmp-commands.hx
>> index cbf1280..8ad06d0 100644
>> --- a/qmp-commands.hx
>> +++ b/qmp-commands.hx
>> @@ -466,6 +466,40 @@ Note: inject-nmi fails when the guest doesn't support injecting.
>>   EQMP
>>   
>>       {
>> +        .name       = "memchar-write",
>> +        .args_type  = "chardev:s,size:i,data:s,format:s?",
>> +        .help       = "write size of data to memory chardev",
> Please, drop .help. We only use it for hmp commands.
>
>> +        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
>> +    },
>> +
>> +SQMP
>> +memchar-write
>> +-------------
>> +
>> +Provide writing interface for CirMemCharDriver. Write data to memory
>> +char device.
>> +
>> +Arguments:
>> +
>> +- "chardev": the name of the char device, must be unique (json-string)
>> +- "size": the memory size, in bytes, should be power of 2 (json-int)
>> +- "data": the source data write to memory (json-string)
>> +- "format": the data format write to memory, default is
>> +            utf8. (json-string, optional)
>> +          - Possible values: "utf8", "base64"
>> +
>> +Example:
>> +
>> +-> { "execute": "memchar-write",
>> +                "arguments": { "chardev": foo,
>> +                               "size": 8,
>> +                               "data": "abcdefgh",
>> +                               "format": "utf8" } }
>> +<- { "return": {} }
>> +
>> +EQMP
>> +
>> +    {
>>           .name       = "xen-save-devices-state",
>>           .args_type  = "filename:F",
>>       .mhandler.cmd_new = qmp_marshal_input_xen_save_devices_state,
>
Luiz Capitulino - Jan. 23, 2013, 3:39 p.m.
On Wed, 23 Jan 2013 11:30:23 +0800
Lei Li <lilei@linux.vnet.ibm.com> wrote:

> On 01/23/2013 12:27 AM, Luiz Capitulino wrote:
> > On Tue, 22 Jan 2013 16:12:51 +0800
> > Lei Li <lilei@linux.vnet.ibm.com> wrote:
> >
> >> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> >> ---
> >>   hmp-commands.hx  |   16 ++++++++++++++++
> >>   hmp.c            |   13 +++++++++++++
> >>   hmp.h            |    1 +
> >>   qapi-schema.json |   41 +++++++++++++++++++++++++++++++++++++++++
> >>   qemu-char.c      |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
> >>   qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
> >>   6 files changed, 153 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/hmp-commands.hx b/hmp-commands.hx
> >> index 0934b9b..e546c76 100644
> >> --- a/hmp-commands.hx
> >> +++ b/hmp-commands.hx
> >> @@ -837,6 +837,22 @@ STEXI
> >>   @item nmi @var{cpu}
> >>   @findex nmi
> >>   Inject an NMI on the given CPU (x86 only).
> >> +
> >> +ETEXI
> >> +
> >> +    {
> >> +        .name       = "memchar_write",
> >> +        .args_type  = "chardev:s,data:s",
> >> +        .params     = "chardev data",
> > This is missing .help. Please look at the other entries for examples.
> 
> Hmm, I did add .help here before version 5, and I get rid of them
> based on your comments "Help doesn't make sense for HMP."...

Did I really say that? The help text makes sense _only_ for HMP.

I may have quoted the wrong .hx file. If I did that I'm sorry, but it's
also just a matter of checking other entries in the file to see if
yours is correct.

Patch

diff --git a/hmp-commands.hx b/hmp-commands.hx
index 0934b9b..e546c76 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -837,6 +837,22 @@  STEXI
 @item nmi @var{cpu}
 @findex nmi
 Inject an NMI on the given CPU (x86 only).
+
+ETEXI
+
+    {
+        .name       = "memchar_write",
+        .args_type  = "chardev:s,data:s",
+        .params     = "chardev data",
+        .mhandler.cmd = hmp_memchar_write,
+    },
+
+STEXI
+@item memchar_write @var{chardev} @var{data}
+@findex memchar_write
+Provide writing interface for CirMemCharDriver. Write @var{data}
+to char device 'memory'.
+
 ETEXI
 
     {
diff --git a/hmp.c b/hmp.c
index c7b6ba0..546d687 100644
--- a/hmp.c
+++ b/hmp.c
@@ -684,6 +684,19 @@  void hmp_pmemsave(Monitor *mon, const QDict *qdict)
     hmp_handle_error(mon, &errp);
 }
 
+void hmp_memchar_write(Monitor *mon, const QDict *qdict)
+{
+    uint32_t size;
+    const char *chardev = qdict_get_str(qdict, "chardev");
+    const char *data = qdict_get_str(qdict, "data");
+    Error *errp = NULL;
+
+    size = strlen(data);
+    qmp_memchar_write(chardev, size, data, false, 0, &errp);
+
+    hmp_handle_error(mon, &errp);
+}
+
 static void hmp_cont_cb(void *opaque, int err)
 {
     if (!err) {
diff --git a/hmp.h b/hmp.h
index 44be683..06d6ea2 100644
--- a/hmp.h
+++ b/hmp.h
@@ -43,6 +43,7 @@  void hmp_system_powerdown(Monitor *mon, const QDict *qdict);
 void hmp_cpu(Monitor *mon, const QDict *qdict);
 void hmp_memsave(Monitor *mon, const QDict *qdict);
 void hmp_pmemsave(Monitor *mon, const QDict *qdict);
+void hmp_memchar_write(Monitor *mon, const QDict *qdict);
 void hmp_cont(Monitor *mon, const QDict *qdict);
 void hmp_system_wakeup(Monitor *mon, const QDict *qdict);
 void hmp_inject_nmi(Monitor *mon, const QDict *qdict);
diff --git a/qapi-schema.json b/qapi-schema.json
index 6d7252b..c34e9ac 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -325,6 +325,47 @@ 
 { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
 
 ##
+# @DataFormat:
+#
+# An enumeration of data format.
+#
+# @utf8: The data format is 'utf8'.
+#
+# @base64: The data format is 'base64'.
+#
+# Since: 1.4
+##
+{ 'enum': 'DataFormat'
+  'data': [ 'utf8', 'base64' ] }
+
+##
+# @memchar-write:
+#
+# Provide writing interface for memchardev. Write data to char
+# device 'memory'.
+#
+# @chardev: the name of the memory char device.
+#
+# @size: the size to write in bytes.
+#
+# @data: the source data write to memchar.
+#
+# @format: #optional the format of the data write to chardev 'memory',
+#          by default is 'utf8'.
+#
+# Returns: Nothing on success
+#          If @chardev is not a valid char device, DeviceNotFound
+#
+# Notes: For now assume 'drop' behaver, which would result in writes
+#        dropping queued data.
+#
+# Since: 1.4
+##
+{ 'command': 'memchar-write',
+  'data': {'chardev': 'str', 'size': 'int', 'data': 'str',
+           '*format': 'DataFormat'} }
+
+##
 # @CommandInfo:
 #
 # Information about a QMP command
diff --git a/qemu-char.c b/qemu-char.c
index b323e94..c3bb6ec 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2754,6 +2754,54 @@  fail:
     return NULL;
 }
 
+static bool qemu_is_chr(const CharDriverState *chr, const char *filename)
+{
+    return strcmp(chr->filename, filename);
+}
+
+void qmp_memchar_write(const char *chardev, int64_t size,
+                       const char *data, bool has_format,
+                       enum DataFormat format,
+                       Error **errp)
+{
+    CharDriverState *chr;
+    guchar *write_data;
+    int ret;
+    gsize write_count;
+
+    chr = qemu_chr_find(chardev);
+    if (!chr) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, chardev);
+        return;
+    }
+
+    if (qemu_is_chr(chr, "memory")) {
+        error_setg(errp,"%s is not memory char device\n", chardev);
+        return;
+    }
+
+    /* XXX: Drop the coming data when the buffer is full. */
+    if (cirmem_chr_is_full(chr)) {
+        error_setg(errp, "Memory device %s is full", chardev);
+        return;
+    }
+
+    write_count = (gsize)size;
+
+    if (has_format && (format == DATA_FORMAT_BASE64)) {
+        write_data = g_base64_decode(data, &write_count);
+    } else {
+        write_data = (uint8_t *)data;
+    }
+
+    ret = cirmem_chr_write(chr, write_data, write_count);
+
+    if (ret < 0) {
+        error_setg(errp, "Failed to write to device %s", chardev);
+        return;
+    }
+}
+
 QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
 {
     char host[65], port[33], width[8], height[8];
diff --git a/qmp-commands.hx b/qmp-commands.hx
index cbf1280..8ad06d0 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -466,6 +466,40 @@  Note: inject-nmi fails when the guest doesn't support injecting.
 EQMP
 
     {
+        .name       = "memchar-write",
+        .args_type  = "chardev:s,size:i,data:s,format:s?",
+        .help       = "write size of data to memory chardev",
+        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
+    },
+
+SQMP
+memchar-write
+-------------
+
+Provide writing interface for CirMemCharDriver. Write data to memory
+char device.
+
+Arguments:
+
+- "chardev": the name of the char device, must be unique (json-string)
+- "size": the memory size, in bytes, should be power of 2 (json-int)
+- "data": the source data write to memory (json-string)
+- "format": the data format write to memory, default is
+            utf8. (json-string, optional)
+          - Possible values: "utf8", "base64"
+
+Example:
+
+-> { "execute": "memchar-write",
+                "arguments": { "chardev": foo,
+                               "size": 8,
+                               "data": "abcdefgh",
+                               "format": "utf8" } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "xen-save-devices-state",
         .args_type  = "filename:F",
     .mhandler.cmd_new = qmp_marshal_input_xen_save_devices_state,