Patchwork [2/4] QAPI: Introduce memchar-write QMP command

login
register
mail settings
Submitter Lei Li
Date Oct. 26, 2012, 11:21 a.m.
Message ID <1351250512-6386-3-git-send-email-lilei@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/194442/
State New
Headers show

Comments

Lei Li - Oct. 26, 2012, 11:21 a.m.
Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 hmp-commands.hx  |   17 +++++++++++++++++
 hmp.c            |   15 +++++++++++++++
 hmp.h            |    1 +
 qapi-schema.json |   47 +++++++++++++++++++++++++++++++++++++++++++++++
 qemu-char.c      |   44 ++++++++++++++++++++++++++++++++++++++++++++
 qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
 6 files changed, 158 insertions(+), 0 deletions(-)
Luiz Capitulino - Oct. 26, 2012, 5:17 p.m.
On Fri, 26 Oct 2012 19:21:50 +0800
Lei Li <lilei@linux.vnet.ibm.com> wrote:

> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> ---
>  hmp-commands.hx  |   17 +++++++++++++++++
>  hmp.c            |   15 +++++++++++++++
>  hmp.h            |    1 +
>  qapi-schema.json |   47 +++++++++++++++++++++++++++++++++++++++++++++++
>  qemu-char.c      |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
>  6 files changed, 158 insertions(+), 0 deletions(-)
> 
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index e0b537d..a37b8e9 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -825,6 +825,23 @@ 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 cirmemchr char device. Note that we  will add 'control' options
> +for read and write command that specifies behavior when the queue
> +is full/empty, for now just assume a drop behaver in these two commands.

You can drop everything after "Note".

> +
> +ETEXI
> +
> +    {
>          .name       = "migrate",
>          .args_type  = "detach:-d,blk:-b,inc:-i,uri:s",
>          .params     = "[-d] [-b] [-i] uri",
> diff --git a/hmp.c b/hmp.c
> index 2b97982..082985b 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -683,6 +683,21 @@ 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");
> +    enum DataFormat format;

Why do you need this variable?

> +    Error *errp = NULL;
> +
> +    size = strlen(data);
> +    format = DATA_FORMAT_UTF8;
> +    qmp_memchar_write(chardev, size, data, true, format, &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 71ea384..406ebb1 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 c615ee2..43ef6bc 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -325,6 +325,53 @@
>  { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
>  
>  ##
> +# @DataFormat:
> +#
> +# An enumeration of data format. The default value would
> +# be utf8.

Please, remove the "default value" part. This is decided by the command
using this type.

> +#
> +# @utf8: The data format is 'utf8'.
> +#
> +# @base64: The data format is 'base64'.
> +#
> +# Note: The data format start with 'utf8' and 'base64',
> +#       will support other data format as well.

Please, drop this note. It's not needed.

> +#
> +# Since: 1.3
> +##
> +{ 'enum': 'DataFormat'
> +  'data': [ 'utf8', 'base64' ] }
> +
> +##
> +# @memchar-write:
> +#
> +# Provide writing interface for memchardev. Write data to memchar
> +# char device.
> +#
> +# @chardev: the name of the memchar char device.
> +#
> +# @size: the size to write in bytes. Should be power of 2.
> +#
> +# @data: the source data write to memchar.
> +#
> +# @format: #optional the format of the data write to memchardev, by
> +#          default is 'utf8'.
> +#
> +# Returns: Nothing on success
> +#          If @chardev is not a valid memchr device, DeviceNotFound
> +#
> +# Notes: The option 'block' is not supported now due to the miss
> +#        feature in qmp. Will add it later when we gain the necessary
> +#        infrastructure enhancement. For now just assume 'drop' behaver
> +#        for this command.

Please, replace this note with an explanation of the current behavior. No
need to talk about the future.

> +#
> +# Since: 1.3
> +##
> +{ '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 c3ec43d..6114e29 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -2717,6 +2717,50 @@ fail:
>      return NULL;
>  }
>  
> +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 (strcmp(chr->filename, "memchr") != 0) {
> +        error_setg(errp,"%s is not memory char device\n", chardev);
> +        return;
> +    }

This is wrong, as it's unreliable. A hackish (but hopefully correct) way
of doing this would be to check chr->init against the circmem init function.
But please, put this behind a function because it's ugly.

> +
> +    /* XXX: For the sync command as 'block', waiting for the qmp
> +     * to support necessary feature. Now just act as 'drop' */

Please, replace this note with an explanation of the current behavior.

> +    if (cirmem_chr_is_full(chr)) {
> +        error_setg(errp, "Failed to write to memchr %s", 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);

IIRC circmem_chr_write() doesn't check if write_count if a power of two,
what happens if it isn't?

> +
> +    if (ret < 0) {
> +        error_setg(errp, "Failed to write to memchr %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 5ba8c48..7548b9b 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?,control:s?",

You've dropped 'control', haven't you?

> +        .help       = "write size of data to memchar chardev",
> +        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
> +    },
> +
> +SQMP
> +memchar-write
> +-------------
> +
> +Provide writing interface for memchardev. Write data to memchar
> +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 writed to memchar (json-string)
> +- "format": the data format write to memchardev, 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 - Oct. 29, 2012, 4:10 a.m.
On 10/27/2012 01:17 AM, Luiz Capitulino wrote:
> On Fri, 26 Oct 2012 19:21:50 +0800
> Lei Li <lilei@linux.vnet.ibm.com> wrote:
>
>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>> ---
>>   hmp-commands.hx  |   17 +++++++++++++++++
>>   hmp.c            |   15 +++++++++++++++
>>   hmp.h            |    1 +
>>   qapi-schema.json |   47 +++++++++++++++++++++++++++++++++++++++++++++++
>>   qemu-char.c      |   44 ++++++++++++++++++++++++++++++++++++++++++++
>>   qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
>>   6 files changed, 158 insertions(+), 0 deletions(-)
>>
>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>> index e0b537d..a37b8e9 100644
>> --- a/hmp-commands.hx
>> +++ b/hmp-commands.hx
>> @@ -825,6 +825,23 @@ 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 cirmemchr char device. Note that we  will add 'control' options
>> +for read and write command that specifies behavior when the queue
>> +is full/empty, for now just assume a drop behaver in these two commands.
> You can drop everything after "Note".
>
ok

>> +
>> +ETEXI
>> +
>> +    {
>>           .name       = "migrate",
>>           .args_type  = "detach:-d,blk:-b,inc:-i,uri:s",
>>           .params     = "[-d] [-b] [-i] uri",
>> diff --git a/hmp.c b/hmp.c
>> index 2b97982..082985b 100644
>> --- a/hmp.c
>> +++ b/hmp.c
>> @@ -683,6 +683,21 @@ 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");
>> +    enum DataFormat format;
> Why do you need this variable?

Sure, I will drop this.

>> +    Error *errp = NULL;
>> +
>> +    size = strlen(data);
>> +    format = DATA_FORMAT_UTF8;
>> +    qmp_memchar_write(chardev, size, data, true, format, &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 71ea384..406ebb1 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 c615ee2..43ef6bc 100644
>> --- a/qapi-schema.json
>> +++ b/qapi-schema.json
>> @@ -325,6 +325,53 @@
>>   { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
>>   
>>   ##
>> +# @DataFormat:
>> +#
>> +# An enumeration of data format. The default value would
>> +# be utf8.
> Please, remove the "default value" part. This is decided by the command
> using this type.

Now the option format is optional, if it's not set then default by 'utf8'.
I think it's a reasonable behaver. :)

>> +#
>> +# @utf8: The data format is 'utf8'.
>> +#
>> +# @base64: The data format is 'base64'.
>> +#
>> +# Note: The data format start with 'utf8' and 'base64',
>> +#       will support other data format as well.
> Please, drop this note. It's not needed.
>
ok

>> +#
>> +# Since: 1.3
>> +##
>> +{ 'enum': 'DataFormat'
>> +  'data': [ 'utf8', 'base64' ] }
>> +
>> +##
>> +# @memchar-write:
>> +#
>> +# Provide writing interface for memchardev. Write data to memchar
>> +# char device.
>> +#
>> +# @chardev: the name of the memchar char device.
>> +#
>> +# @size: the size to write in bytes. Should be power of 2.
>> +#
>> +# @data: the source data write to memchar.
>> +#
>> +# @format: #optional the format of the data write to memchardev, by
>> +#          default is 'utf8'.
>> +#
>> +# Returns: Nothing on success
>> +#          If @chardev is not a valid memchr device, DeviceNotFound
>> +#
>> +# Notes: The option 'block' is not supported now due to the miss
>> +#        feature in qmp. Will add it later when we gain the necessary
>> +#        infrastructure enhancement. For now just assume 'drop' behaver
>> +#        for this command.
> Please, replace this note with an explanation of the current behavior. No
> need to talk about the future.

Sure.

>> +#
>> +# Since: 1.3
>> +##
>> +{ '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 c3ec43d..6114e29 100644
>> --- a/qemu-char.c
>> +++ b/qemu-char.c
>> @@ -2717,6 +2717,50 @@ fail:
>>       return NULL;
>>   }
>>   
>> +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 (strcmp(chr->filename, "memchr") != 0) {
>> +        error_setg(errp,"%s is not memory char device\n", chardev);
>> +        return;
>> +    }
> This is wrong, as it's unreliable. A hackish (but hopefully correct) way
> of doing this would be to check chr->init against the circmem init function.
> But please, put this behind a function because it's ugly.

Hmm, I guess it's because the chr->filename could be NULL. but we can still
get it since CharDriverState keeps the inited type of backend. I am not sure
that check chr->init against the cirmem init funciton could work, I'll have
a try.

>
>> +
>> +    /* XXX: For the sync command as 'block', waiting for the qmp
>> +     * to support necessary feature. Now just act as 'drop' */
> Please, replace this note with an explanation of the current behavior.

ok.

>> +    if (cirmem_chr_is_full(chr)) {
>> +        error_setg(errp, "Failed to write to memchr %s", 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);
> IIRC circmem_chr_write() doesn't check if write_count if a power of two,
> what happens if it isn't?

I have considered your suggestion on this in v4. The reason why I did not
add the assert is that I think we have already check with this when cirmem
init, so there is no need to check it again. Correct me if I am wrong. :)

>> +
>> +    if (ret < 0) {
>> +        error_setg(errp, "Failed to write to memchr %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 5ba8c48..7548b9b 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?,control:s?",
> You've dropped 'control', haven't you?

Yes, sorry I forgot to drop here.. :(

>
>> +        .help       = "write size of data to memchar chardev",
>> +        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
>> +    },
>> +
>> +SQMP
>> +memchar-write
>> +-------------
>> +
>> +Provide writing interface for memchardev. Write data to memchar
>> +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 writed to memchar (json-string)
>> +- "format": the data format write to memchardev, 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 - Oct. 29, 2012, 1:23 p.m.
On Mon, 29 Oct 2012 12:10:24 +0800
Lei Li <lilei@linux.vnet.ibm.com> wrote:

> On 10/27/2012 01:17 AM, Luiz Capitulino wrote:
> > On Fri, 26 Oct 2012 19:21:50 +0800
> > Lei Li <lilei@linux.vnet.ibm.com> wrote:
> >
> >> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> >> ---
> >>   hmp-commands.hx  |   17 +++++++++++++++++
> >>   hmp.c            |   15 +++++++++++++++
> >>   hmp.h            |    1 +
> >>   qapi-schema.json |   47 +++++++++++++++++++++++++++++++++++++++++++++++
> >>   qemu-char.c      |   44 ++++++++++++++++++++++++++++++++++++++++++++
> >>   qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
> >>   6 files changed, 158 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/hmp-commands.hx b/hmp-commands.hx
> >> index e0b537d..a37b8e9 100644
> >> --- a/hmp-commands.hx
> >> +++ b/hmp-commands.hx
> >> @@ -825,6 +825,23 @@ 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 cirmemchr char device. Note that we  will add 'control' options
> >> +for read and write command that specifies behavior when the queue
> >> +is full/empty, for now just assume a drop behaver in these two commands.
> > You can drop everything after "Note".
> >
> ok
> 
> >> +
> >> +ETEXI
> >> +
> >> +    {
> >>           .name       = "migrate",
> >>           .args_type  = "detach:-d,blk:-b,inc:-i,uri:s",
> >>           .params     = "[-d] [-b] [-i] uri",
> >> diff --git a/hmp.c b/hmp.c
> >> index 2b97982..082985b 100644
> >> --- a/hmp.c
> >> +++ b/hmp.c
> >> @@ -683,6 +683,21 @@ 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");
> >> +    enum DataFormat format;
> > Why do you need this variable?
> 
> Sure, I will drop this.
> 
> >> +    Error *errp = NULL;
> >> +
> >> +    size = strlen(data);
> >> +    format = DATA_FORMAT_UTF8;
> >> +    qmp_memchar_write(chardev, size, data, true, format, &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 71ea384..406ebb1 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 c615ee2..43ef6bc 100644
> >> --- a/qapi-schema.json
> >> +++ b/qapi-schema.json
> >> @@ -325,6 +325,53 @@
> >>   { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
> >>   
> >>   ##
> >> +# @DataFormat:
> >> +#
> >> +# An enumeration of data format. The default value would
> >> +# be utf8.
> > Please, remove the "default value" part. This is decided by the command
> > using this type.
> 
> Now the option format is optional, if it's not set then default by 'utf8'.
> I think it's a reasonable behaver. :)

What I meant is that the right place to say what the value is is in
the command documentation, not in @DataFormat doc. Here, only having
"An enumeration of data encodings" is fine.

> >> +#
> >> +# @utf8: The data format is 'utf8'.
> >> +#
> >> +# @base64: The data format is 'base64'.
> >> +#
> >> +# Note: The data format start with 'utf8' and 'base64',
> >> +#       will support other data format as well.
> > Please, drop this note. It's not needed.
> >
> ok
> 
> >> +#
> >> +# Since: 1.3
> >> +##
> >> +{ 'enum': 'DataFormat'
> >> +  'data': [ 'utf8', 'base64' ] }
> >> +
> >> +##
> >> +# @memchar-write:
> >> +#
> >> +# Provide writing interface for memchardev. Write data to memchar
> >> +# char device.
> >> +#
> >> +# @chardev: the name of the memchar char device.
> >> +#
> >> +# @size: the size to write in bytes. Should be power of 2.
> >> +#
> >> +# @data: the source data write to memchar.
> >> +#
> >> +# @format: #optional the format of the data write to memchardev, by
> >> +#          default is 'utf8'.
> >> +#
> >> +# Returns: Nothing on success
> >> +#          If @chardev is not a valid memchr device, DeviceNotFound
> >> +#
> >> +# Notes: The option 'block' is not supported now due to the miss
> >> +#        feature in qmp. Will add it later when we gain the necessary
> >> +#        infrastructure enhancement. For now just assume 'drop' behaver
> >> +#        for this command.
> > Please, replace this note with an explanation of the current behavior. No
> > need to talk about the future.
> 
> Sure.
> 
> >> +#
> >> +# Since: 1.3
> >> +##
> >> +{ '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 c3ec43d..6114e29 100644
> >> --- a/qemu-char.c
> >> +++ b/qemu-char.c
> >> @@ -2717,6 +2717,50 @@ fail:
> >>       return NULL;
> >>   }
> >>   
> >> +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 (strcmp(chr->filename, "memchr") != 0) {
> >> +        error_setg(errp,"%s is not memory char device\n", chardev);
> >> +        return;
> >> +    }
> > This is wrong, as it's unreliable. A hackish (but hopefully correct) way
> > of doing this would be to check chr->init against the circmem init function.
> > But please, put this behind a function because it's ugly.
> 
> Hmm, I guess it's because the chr->filename could be NULL. but we can still
> get it since CharDriverState keeps the inited type of backend. I am not sure
> that check chr->init against the cirmem init funciton could work, I'll have
> a try.
> 
> >
> >> +
> >> +    /* XXX: For the sync command as 'block', waiting for the qmp
> >> +     * to support necessary feature. Now just act as 'drop' */
> > Please, replace this note with an explanation of the current behavior.
> 
> ok.
> 
> >> +    if (cirmem_chr_is_full(chr)) {
> >> +        error_setg(errp, "Failed to write to memchr %s", 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);
> > IIRC circmem_chr_write() doesn't check if write_count if a power of two,
> > what happens if it isn't?
> 
> I have considered your suggestion on this in v4. The reason why I did not
> add the assert is that I think we have already check with this when cirmem
> init, so there is no need to check it again. Correct me if I am wrong. :)

I was actually asking an honest question: does cirmem_chr_write() assume
that len is a power of two? If yes, what if the user doesn't pass a
power of two value to qmp_memchar_write()?

> 
> >> +
> >> +    if (ret < 0) {
> >> +        error_setg(errp, "Failed to write to memchr %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 5ba8c48..7548b9b 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?,control:s?",
> > You've dropped 'control', haven't you?
> 
> Yes, sorry I forgot to drop here.. :(
> 
> >
> >> +        .help       = "write size of data to memchar chardev",
> >> +        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
> >> +    },
> >> +
> >> +SQMP
> >> +memchar-write
> >> +-------------
> >> +
> >> +Provide writing interface for memchardev. Write data to memchar
> >> +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 writed to memchar (json-string)
> >> +- "format": the data format write to memchardev, 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 - Oct. 30, 2012, 10:22 a.m.
On 10/29/2012 09:23 PM, Luiz Capitulino wrote:
> On Mon, 29 Oct 2012 12:10:24 +0800
> Lei Li <lilei@linux.vnet.ibm.com> wrote:
>
>> On 10/27/2012 01:17 AM, Luiz Capitulino wrote:
>>> On Fri, 26 Oct 2012 19:21:50 +0800
>>> Lei Li <lilei@linux.vnet.ibm.com> wrote:
>>>
>>>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>>>> ---
>>>>    hmp-commands.hx  |   17 +++++++++++++++++
>>>>    hmp.c            |   15 +++++++++++++++
>>>>    hmp.h            |    1 +
>>>>    qapi-schema.json |   47 +++++++++++++++++++++++++++++++++++++++++++++++
>>>>    qemu-char.c      |   44 ++++++++++++++++++++++++++++++++++++++++++++
>>>>    qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++++
>>>>    6 files changed, 158 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>>>> index e0b537d..a37b8e9 100644
>>>> --- a/hmp-commands.hx
>>>> +++ b/hmp-commands.hx
>>>> @@ -825,6 +825,23 @@ 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 cirmemchr char device. Note that we  will add 'control' options
>>>> +for read and write command that specifies behavior when the queue
>>>> +is full/empty, for now just assume a drop behaver in these two commands.
>>> You can drop everything after "Note".
>>>
>> ok
>>
>>>> +
>>>> +ETEXI
>>>> +
>>>> +    {
>>>>            .name       = "migrate",
>>>>            .args_type  = "detach:-d,blk:-b,inc:-i,uri:s",
>>>>            .params     = "[-d] [-b] [-i] uri",
>>>> diff --git a/hmp.c b/hmp.c
>>>> index 2b97982..082985b 100644
>>>> --- a/hmp.c
>>>> +++ b/hmp.c
>>>> @@ -683,6 +683,21 @@ 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");
>>>> +    enum DataFormat format;
>>> Why do you need this variable?
>> Sure, I will drop this.
>>
>>>> +    Error *errp = NULL;
>>>> +
>>>> +    size = strlen(data);
>>>> +    format = DATA_FORMAT_UTF8;
>>>> +    qmp_memchar_write(chardev, size, data, true, format, &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 71ea384..406ebb1 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 c615ee2..43ef6bc 100644
>>>> --- a/qapi-schema.json
>>>> +++ b/qapi-schema.json
>>>> @@ -325,6 +325,53 @@
>>>>    { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
>>>>    
>>>>    ##
>>>> +# @DataFormat:
>>>> +#
>>>> +# An enumeration of data format. The default value would
>>>> +# be utf8.
>>> Please, remove the "default value" part. This is decided by the command
>>> using this type.
>> Now the option format is optional, if it's not set then default by 'utf8'.
>> I think it's a reasonable behaver. :)
> What I meant is that the right place to say what the value is is in
> the command documentation, not in @DataFormat doc. Here, only having
> "An enumeration of data encodings" is fine.

OK, done.

>>>> +#
>>>> +# @utf8: The data format is 'utf8'.
>>>> +#
>>>> +# @base64: The data format is 'base64'.
>>>> +#
>>>> +# Note: The data format start with 'utf8' and 'base64',
>>>> +#       will support other data format as well.
>>> Please, drop this note. It's not needed.
>>>
>> ok
>>
>>>> +#
>>>> +# Since: 1.3
>>>> +##
>>>> +{ 'enum': 'DataFormat'
>>>> +  'data': [ 'utf8', 'base64' ] }
>>>> +
>>>> +##
>>>> +# @memchar-write:
>>>> +#
>>>> +# Provide writing interface for memchardev. Write data to memchar
>>>> +# char device.
>>>> +#
>>>> +# @chardev: the name of the memchar char device.
>>>> +#
>>>> +# @size: the size to write in bytes. Should be power of 2.
>>>> +#
>>>> +# @data: the source data write to memchar.
>>>> +#
>>>> +# @format: #optional the format of the data write to memchardev, by
>>>> +#          default is 'utf8'.
>>>> +#
>>>> +# Returns: Nothing on success
>>>> +#          If @chardev is not a valid memchr device, DeviceNotFound
>>>> +#
>>>> +# Notes: The option 'block' is not supported now due to the miss
>>>> +#        feature in qmp. Will add it later when we gain the necessary
>>>> +#        infrastructure enhancement. For now just assume 'drop' behaver
>>>> +#        for this command.
>>> Please, replace this note with an explanation of the current behavior. No
>>> need to talk about the future.
>> Sure.
>>
>>>> +#
>>>> +# Since: 1.3
>>>> +##
>>>> +{ '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 c3ec43d..6114e29 100644
>>>> --- a/qemu-char.c
>>>> +++ b/qemu-char.c
>>>> @@ -2717,6 +2717,50 @@ fail:
>>>>        return NULL;
>>>>    }
>>>>    
>>>> +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 (strcmp(chr->filename, "memchr") != 0) {
>>>> +        error_setg(errp,"%s is not memory char device\n", chardev);
>>>> +        return;
>>>> +    }
>>> This is wrong, as it's unreliable. A hackish (but hopefully correct) way
>>> of doing this would be to check chr->init against the circmem init function.
>>> But please, put this behind a function because it's ugly.
>> Hmm, I guess it's because the chr->filename could be NULL. but we can still
>> get it since CharDriverState keeps the inited type of backend. I am not sure
>> that check chr->init against the cirmem init funciton could work, I'll have
>> a try.
>>
>>>> +
>>>> +    /* XXX: For the sync command as 'block', waiting for the qmp
>>>> +     * to support necessary feature. Now just act as 'drop' */
>>> Please, replace this note with an explanation of the current behavior.
>> ok.
>>
>>>> +    if (cirmem_chr_is_full(chr)) {
>>>> +        error_setg(errp, "Failed to write to memchr %s", 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);
>>> IIRC circmem_chr_write() doesn't check if write_count if a power of two,
>>> what happens if it isn't?
>> I have considered your suggestion on this in v4. The reason why I did not
>> add the assert is that I think we have already check with this when cirmem
>> init, so there is no need to check it again. Correct me if I am wrong. :)
> I was actually asking an honest question: does cirmem_chr_write() assume
> that len is a power of two? If yes, what if the user doesn't pass a
> power of two value to qmp_memchar_write()?

Ah, there must be some misunderstanding here... :) We let the size of ring
buffer inited as power of 2, not the write_count. And it has already been
checked when we init the CirMemCharDriver. That's why I did not
add the assert in the function cirmem_chr_write.

>
>>>> +
>>>> +    if (ret < 0) {
>>>> +        error_setg(errp, "Failed to write to memchr %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 5ba8c48..7548b9b 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?,control:s?",
>>> You've dropped 'control', haven't you?
>> Yes, sorry I forgot to drop here.. :(
>>
>>>> +        .help       = "write size of data to memchar chardev",
>>>> +        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
>>>> +    },
>>>> +
>>>> +SQMP
>>>> +memchar-write
>>>> +-------------
>>>> +
>>>> +Provide writing interface for memchardev. Write data to memchar
>>>> +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 writed to memchar (json-string)
>>>> +- "format": the data format write to memchardev, 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,
>>

Patch

diff --git a/hmp-commands.hx b/hmp-commands.hx
index e0b537d..a37b8e9 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -825,6 +825,23 @@  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 cirmemchr char device. Note that we  will add 'control' options
+for read and write command that specifies behavior when the queue
+is full/empty, for now just assume a drop behaver in these two commands.
+
+ETEXI
+
+    {
         .name       = "migrate",
         .args_type  = "detach:-d,blk:-b,inc:-i,uri:s",
         .params     = "[-d] [-b] [-i] uri",
diff --git a/hmp.c b/hmp.c
index 2b97982..082985b 100644
--- a/hmp.c
+++ b/hmp.c
@@ -683,6 +683,21 @@  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");
+    enum DataFormat format;
+    Error *errp = NULL;
+
+    size = strlen(data);
+    format = DATA_FORMAT_UTF8;
+    qmp_memchar_write(chardev, size, data, true, format, &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 71ea384..406ebb1 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 c615ee2..43ef6bc 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -325,6 +325,53 @@ 
 { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
 
 ##
+# @DataFormat:
+#
+# An enumeration of data format. The default value would
+# be utf8.
+#
+# @utf8: The data format is 'utf8'.
+#
+# @base64: The data format is 'base64'.
+#
+# Note: The data format start with 'utf8' and 'base64',
+#       will support other data format as well.
+#
+# Since: 1.3
+##
+{ 'enum': 'DataFormat'
+  'data': [ 'utf8', 'base64' ] }
+
+##
+# @memchar-write:
+#
+# Provide writing interface for memchardev. Write data to memchar
+# char device.
+#
+# @chardev: the name of the memchar char device.
+#
+# @size: the size to write in bytes. Should be power of 2.
+#
+# @data: the source data write to memchar.
+#
+# @format: #optional the format of the data write to memchardev, by
+#          default is 'utf8'.
+#
+# Returns: Nothing on success
+#          If @chardev is not a valid memchr device, DeviceNotFound
+#
+# Notes: The option 'block' is not supported now due to the miss
+#        feature in qmp. Will add it later when we gain the necessary
+#        infrastructure enhancement. For now just assume 'drop' behaver
+#        for this command.
+#
+# Since: 1.3
+##
+{ '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 c3ec43d..6114e29 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2717,6 +2717,50 @@  fail:
     return NULL;
 }
 
+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 (strcmp(chr->filename, "memchr") != 0) {
+        error_setg(errp,"%s is not memory char device\n", chardev);
+        return;
+    }
+
+    /* XXX: For the sync command as 'block', waiting for the qmp
+     * to support necessary feature. Now just act as 'drop' */
+    if (cirmem_chr_is_full(chr)) {
+        error_setg(errp, "Failed to write to memchr %s", 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 memchr %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 5ba8c48..7548b9b 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?,control:s?",
+        .help       = "write size of data to memchar chardev",
+        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
+    },
+
+SQMP
+memchar-write
+-------------
+
+Provide writing interface for memchardev. Write data to memchar
+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 writed to memchar (json-string)
+- "format": the data format write to memchardev, 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,