Re: [Qemu-devel] [PATCH 3/5] QAPI: Introduce memchar-write QMP command

[Luiz Capitulino]

On Thu, 20 Sep 2012 15:42:30 +0800
Lei Li <address@hidden> wrote:

> On 09/20/2012 02:05 AM, Luiz Capitulino wrote:
> > On Wed, 12 Sep 2012 19:57:24 +0800
> > Lei Li <address@hidden> wrote:
> >
> >> Signed-off-by: Lei Li <address@hidden>
> >> ---
> >>   hmp-commands.hx  |   23 ++++++++++++++++++
> >>   hmp.c            |   19 +++++++++++++++
> >>   hmp.h            |    1 +
> >>   qapi-schema.json |   69 
> >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>   qemu-char.c      |   48 +++++++++++++++++++++++++++++++++++++
> >>   qmp-commands.hx  |   39 ++++++++++++++++++++++++++++++
> >>   6 files changed, 199 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/hmp-commands.hx b/hmp-commands.hx
> >> index ed67e99..fe11926 100644
> >> --- a/hmp-commands.hx
> >> +++ b/hmp-commands.hx
> >> @@ -796,6 +796,29 @@ Inject an NMI on the given CPU (x86 only).
> >>   ETEXI
> >>   
> >>       {
> >> +        .name       = "memchar_write",
> >> +        .args_type  = "chardev:s,size:i,data:s,format:s?,control:s?",
> >> +        .params     = "chardev size data [format] [control]",
> >> +        .help       = "Provide writing interface for CirMemCharDriver. 
> >> Write"
> >> +                      "'data' to it with size 'size'",
> >> +        .mhandler.cmd = hmp_memchar_write,
> >> +    },
> > That's a too low level command for hmp. I'd actually consider dropping
> > it in favor of the console command, but if you really want to have this
> > then I suggest making the following changes:
> >
> >   o drop 'size', as this can be calculated from the user input string
> >   o drop 'format', as base64 doesn't make much sense for hmp
> >   o turn 'control' into a flag, like -b for block and -d for drop
> >
> > Also applies for memchar_read.
> >
> >> +
> >> +STEXI
> >> address@hidden memchar_write @var{chardev} @var{size} @var{data} 
> >> address@hidden address@hidden
> >> address@hidden memchar_write
> >> +Provide writing interface for CirMemCharDriver. Write @var{data}
> >> +to cirmemchr char device with size @var{size}.
> >> +
> >> address@hidden is the format of the data write to CirMemCharDriver.
> >> +Support 'utf8' and 'base64', by default is 'utf8'.
> >> +
> >> address@hidden is option('block', 'drop') for read and write command
> >> +that specifies behavior when the queue is full/empty. By default is
> >> +'drop'. Note that the 'block' option is not supported now.
> >> +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 ba6fbd3..97f5058 100644
> >> --- a/hmp.c
> >> +++ b/hmp.c
> >> @@ -671,6 +671,25 @@ 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 = qdict_get_int(qdict, "size");
> >> +    const char *chardev = qdict_get_str(qdict, "chardev");
> >> +    const char *data = qdict_get_str(qdict, "data");
> >> +    int val = qdict_get_try_bool(qdict, "base64", 0);
> >> +    enum DataFormat format;
> >> +    int con = qdict_get_try_bool(qdict, "block", 0);
> >> +    enum CongestionControl control;
> >> +    Error *errp = NULL;
> >> +
> >> +    format = val ? DATA_FORMAT_BASE64 : DATA_FORMAT_UTF8;
> >> +    control = con ? CONGESTION_CONTROL_BLOCK : CONGESTION_CONTROL_DROP;
> >> +    qmp_memchar_write(chardev, size, data, true, format,
> >> +                      true, control, &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 48b9c59..44b6463 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 a9f465a..371239a 100644
> >> --- a/qapi-schema.json
> >> +++ b/qapi-schema.json
> >> @@ -236,6 +236,75 @@
> >>   { 'command': 'query-chardev', 'returns': ['ChardevInfo'] }
> >>   
> >>   ##
> >> +# @DataFormat:
> >> +#
> >> +# An enumeration of data format write to or read from
> >> +# memchardev. 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' ] }
> >> +
> >> +##
> >> +# @CongestionControl
> >> +#
> >> +# An enumeration of options for the read and write command that
> >> +# specifies behavior when the queue is full/empty. The default
> >> +# option would be dropped.
> >> +#
> >> +# @drop: Would result in reads returning empty strings and writes
> >> +#        dropping queued data.
> >> +#
> >> +# @block: Would make the session block until data was available
> >> +#         or the queue had space available.
> >> +#
> >> +# Note: 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.
> > That's not acceptable. We either, hold the inclusion of this series
> > until this is ready or we hardcode drop for now and add new commands
> > supporting @CongestionControl later.
> >
> >> +#
> >> +# Since: 1.3
> >> +##
> >> +{'enum': 'CongestionControl'
> >> + 'data': [ 'drop', 'block' ] }
> >> +
> >> +##
> >> +# @memchar-write:
> >> +#
> >> +# Provide writing interface for CirMemCharDriver. Write data to cirmemchar
> >> +# char device.
> >> +#
> >> +# @chardev: the name of the cirmemchar char device.
> >> +#
> >> +# @size: the size to write in bytes.
> >> +#
> >> +# @data: the source data write to cirmemchar.
> >> +#
> >> +# @format: #optional the format of the data write to cirmemchar, by
> >> +#          default is 'utf8'.
> >> +#
> >> +# @control: #optional options for read and write command that specifies
> >> +#           behavior when the queue is full/empty.
> >> +#
> >> +# Returns: Nothing on success
> >> +#          If @chardev is not a valid cirmemchr device, DeviceNotFound
> >> +#          If an I/O error occurs while writing, IOError
> > This last line can be dropped.
> >
> >> +#
> >> +# Since: 1.3
> >> +##
> >> +{ 'command': 'memchar-write',
> >> +  'data': {'chardev': 'str', 'size': 'int', 'data': 'str',
> >> +           '*format': 'DataFormat',
> > I don't think format should be optional.
> >
> >> +           '*control': 'CongestionControl'} }
> >> +
> >> +##
> >>   # @CommandInfo:
> >>   #
> >>   # Information about a QMP command
> >> diff --git a/qemu-char.c b/qemu-char.c
> >> index 6e84acc..be1d79a 100644
> >> --- a/qemu-char.c
> >> +++ b/qemu-char.c
> >> @@ -2700,6 +2700,54 @@ static CharDriverState 
> >> *qemu_chr_open_cirmemchr(QemuOpts *opts)
> >>       return chr;
> >>   }
> >>   
> >> +void qmp_memchar_write(const char *chardev, int64_t size,
> >> +                       const char *data, bool has_format,
> >> +                       enum DataFormat format, bool has_control,
> >> +                       enum CongestionControl control,
> >> +                       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;
> >> +    }
> >> +
> >> +    /* 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)) {
> >> +        if (has_control && (control == CONGESTION_CONTROL_BLOCK)) {
> >> +            g_free((char *)data);
> >> +            return;
> >> +        } else {
> >> +            g_free((char *)data);
> >> +            error_setg(errp, "Failed to write to memchr %s", chardev);
> >> +            return;
> >> +        }
> >> +    }
> > Why do you free data above?
> 
> Like the document motioned, we have two options { 'drop', 'block' } as 
> congestion
> mechanism suggested by Anthony, when set 'drop' would result in reads 
> returning
> empty strings and writes dropping queued data. Set 'block' then we could make 
> the
> session block until data was available or the queue had space available.
> Now free the data for option 'block' too since we lack such infrastructure 
> now,
> will act as 'block' later when we gain the necessary infrastructure 
> enhancement.

The qapi will free 'data' as soon as the command returns, you don't
have/need to do it by hand. You should have seen a double free while
testing this...

> 
> >> +
> >> +    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);
> >> +    }
> >> +
> >> +    g_free(write_data);
> >> +}
> >> +
> >>   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 6e21ddb..5a1b86b 100644
> >> --- a/qmp-commands.hx
> >> +++ b/qmp-commands.hx
> >> @@ -466,6 +466,45 @@ 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?",
> >> +        .mhandler.cmd_new = qmp_marshal_input_memchar_write,
> >> +    },
> >> +
> >> +SQMP
> >> +memchar-write
> >> +-------------
> >> +
> >> +Provide writing interface for CirMemCharDriver. Write data to cirmemchar
> >> +char device.
> >> +
> >> +Arguments:
> >> +
> >> +- "chardev": the name of the char device, must be unique (json-string)
> >> +- "size": the memory size, in bytes (json-int)
> >> +- "data": the source data writed to cirmemchar (json-string)
> >> +- "format": the data format write to CirMemCharDriver, default is
> >> +            utf8. (json-string, optional)
> >> +          - Possible values: "utf8", "base64"
> >> +
> >> +- "control": options for read and write command that specifies
> >> +             behavior when the queue is full/empty, default is
> >> +             drop. (json-string, optional)
> >> +          - Possible values: "drop", "block"
> >> +
> >> +Example:
> >> +
> >> +-> { "execute": "memchar-write",
> >> +                "arguments": { "chardev": foo,
> >> +                               "size": 7,
> >> +                               "data": "abcdefg",
> >> +                               "format": "utf8",
> >> +                               "control": "drop" } }
> >> +<- { "return": {} }
> >> +
> >> +EQMP
> >> +
> >> +    {
> >>           .name       = "xen-save-devices-state",
> >>           .args_type  = "filename:F",
> >>       .mhandler.cmd_new = qmp_marshal_input_xen_save_devices_state,
> >
> 
>