Re: [Qemu-devel] [PATCH 3/4] QAPI: Introduce memchar-read QMP command

[Luiz Capitulino]

On Fri, 26 Oct 2012 19:21:51 +0800
Lei Li <address@hidden> wrote:

> Signed-off-by: Lei Li <address@hidden>
> ---
>  hmp-commands.hx  |   19 ++++++++++++++++++
>  hmp.c            |   19 ++++++++++++++++++
>  hmp.h            |    1 +
>  qapi-schema.json |   27 ++++++++++++++++++++++++++
>  qemu-char.c      |   55 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qmp-commands.hx  |   40 +++++++++++++++++++++++++++++++++++++++
>  6 files changed, 161 insertions(+), 0 deletions(-)
> 
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index a37b8e9..df294eb 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -842,6 +842,25 @@ is full/empty, for now just assume a drop behaver in 
> these two commands.
>  ETEXI
>  
>      {
> +        .name       = "memchar_read",
> +        .args_type  = "chardev:s,size:i",
> +        .params     = "chardev size",
> +        .mhandler.cmd = hmp_memchar_read,
> +    },
> +
> +STEXI
> address@hidden memchar_read @var{chardev}
> address@hidden memchar_read
> +Provide read interface for CirMemCharDriver. Read from cirmemchr
> +char device and return @var{size} of the data.
> +
> address@hidden is the size of data want to read from. Refer to unencoded
> +size of the raw data, would adjust to the init size of the memchar
> +if the requested size is larger than it.
> +
> +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 082985b..ef85736 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -698,6 +698,25 @@ void hmp_memchar_write(Monitor *mon, const QDict *qdict)
>      hmp_handle_error(mon, &errp);
>  }
>  
> +void hmp_memchar_read(Monitor *mon, const QDict *qdict)
> +{
> +    uint32_t size = qdict_get_int(qdict, "size");
> +    const char *chardev = qdict_get_str(qdict, "chardev");
> +    char *data;
> +    enum DataFormat format;

You don't need this variable.

> +    Error *errp = NULL;
> +
> +    format = DATA_FORMAT_UTF8;
> +    data = qmp_memchar_read(chardev, size, true, format, &errp);
> +    if (errp) {
> +        monitor_printf(mon, "%s\n", error_get_pretty(errp));
> +        error_free(errp);
> +        return;
> +    }
> +
> +    monitor_printf(mon, "%s\n", data);
> +}
> +
>  static void hmp_cont_cb(void *opaque, int err)
>  {
>      if (!err) {
> diff --git a/hmp.h b/hmp.h
> index 406ebb1..a5a0cfe 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -44,6 +44,7 @@ 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_memchar_read(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 43ef6bc..a8c9430 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -372,6 +372,33 @@
>             '*format': 'DataFormat'} }
>  
>  ##
> +# @memchar-read:
> +#
> +# Provide read interface for memchardev. Read from memchar
> +# char device and return the data.
> +#
> +# @chardev: the name of the memchar char device.
> +#
> +# @size: the size to read in bytes.
> +#
> +# @format: #optional the format of the data want to read from
> +#          memchardev, by default is 'utf8'.
> +#
> +# Returns: The data read from memchar as string
> +#          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-read',
> +  'data': {'chardev': 'str', 'size': 'int', '*format': 'DataFormat'},
> +  'returns': 'str' }
> +
> +##
>  # @CommandInfo:
>  #
>  # Information about a QMP command
> diff --git a/qemu-char.c b/qemu-char.c
> index 6114e29..cf88f71 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -2761,6 +2761,61 @@ void qmp_memchar_write(const char *chardev, int64_t 
> size,
>      }
>  }
>  
> +char *qmp_memchar_read(const char *chardev, int64_t size,
> +                       bool has_format, enum DataFormat format,
> +                       Error **errp)
> +{
> +    CharDriverState *chr;
> +    guchar *read_data;
> +    char *data = NULL;
> +    int ret;
> +
> +    read_data = g_malloc0(size);

This is unsafe, as qmp clients could pass any value here. You should check
the number of available bytes and allocate only that.

> +
> +    chr = qemu_chr_find(chardev);
> +    if (!chr) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, chardev);
> +        goto fail;
> +    }
> +
> +    if (strcmp(chr->filename, "memchr") != 0) {
> +        error_setg(errp,"The %s is not memory char device\n", chardev);
> +        goto fail;
> +    }

The same comment I made for the write operation applies here.

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

Here too.

> +    if (cirmem_chr_is_empty(chr)) {
> +        error_setg(errp, "Failed to read from memchr %s", chardev);
> +        goto fail;
> +    }
> +
> +    if (size == 0) {
> +        size = CBUFF_SIZE;
> +    }

IMO, you should refuse size=0.

> +
> +    ret = cirmem_chr_read(chr, read_data, size);
> +
> +    if (ret < 0) {
> +        error_setg(errp, "Failed to read from memchr %s", chardev);
> +        goto fail;
> +    }
> +
> +    if (has_format && (format == DATA_FORMAT_BASE64)) {
> +       if (read_data) {
> +           data = g_base64_encode(read_data, (size_t)size);
> +       }
> +    } else {
> +        data = (char *)read_data;
> +    }
> +
> +    return data;
> +
> +fail:
> +    g_free(read_data);
> +    return NULL;
> +}
> +
>  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 7548b9b..7729fb0 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -500,6 +500,46 @@ Example:
>  EQMP
>  
>      {
> +        .name       = "memchar-read",
> +        .args_type  = "chardev:s,size:i,format:s?",
> +        .help       = "return the size of data from memchar chardev",
> +        .mhandler.cmd_new = qmp_marshal_input_memchar_read,
> +    },
> +
> +SQMP
> +memchar-read
> +-------------
> +
> +Provide read interface for memchardev. Read from memchar
> +char device and return the data.
> +
> +Arguments:
> +
> +- "chardev": the name of the char device, must be unique (json-string)
> +- "size": the memory size wanted to read in bytes(refer to unencoded
> +          size of the raw data), would adjust to the init size of the
> +          memchar if the requested size is larger than it. (json-int)
> +- "format": the data format write to memchardev, default is
> +            utf8. (json-string, optional)
> +          - Possible values: "utf8", "base64"
> +
> +Example:
> +
> +-> { "execute": "memchar-read",
> +                "arguments": { "chardev": foo,
> +                               "size": 1000,
> +                               "format": "utf8" } }
> +<- { "return": "data string..." }
> +
> +Notes:
> +
> +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.

Please drop this.

> +
> +EQMP
> +
> +    {
>          .name       = "xen-save-devices-state",
>          .args_type  = "filename:F",
>      .mhandler.cmd_new = qmp_marshal_input_xen_save_devices_state,