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

[Lei Li <lilei@linux.vnet.ibm.com>]

On 10/29/2012 09:17 PM, Luiz Capitulino wrote:
> On Mon, 29 Oct 2012 12:09:38 +0800
> Lei Li <lilei@linux.vnet.ibm.com> wrote:
>
>> On 10/27/2012 01:39 AM, Luiz Capitulino wrote:
>>> On Fri, 26 Oct 2012 19:21:51 +0800
>>> Lei Li <lilei@linux.vnet.ibm.com> wrote:
>>>
>>>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>>>> ---
>>>>    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
>>>> +@item memchar_read @var{chardev}
>>>> +@findex memchar_read
>>>> +Provide read interface for CirMemCharDriver. Read from cirmemchr
>>>> +char device and return @var{size} of the data.
>>>> +
>>>> +@var{size} 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.
>> ok.
>>
>>>> +    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.
>> ok.
>>
>>>> +#
>>>> +# 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.
>> This size is not the init size of ring buffer, it's the size user want to read
>> from the cirmem backend.
> Yes, it's a temporary buffer and you allocate the exact value passed
> by the user. What if s/he passes 2G?
>
> My suggestion is to limit it to the amount of bytes available in the
> circular buffer.

Done.

>> And it'll be checked within cirmem_chr_write.
> Not sure I get what you mean.
>
>>>> +
>>>> +    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.
>> Do you think it's better to refuse it than giving a default size?
> Down QMP yes.

OK, done.

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


-- 
Lei