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

[Luiz Capitulino]

On Mon, 29 Oct 2012 12:09:38 +0800
Lei Li <address@hidden> wrote:

> On 10/27/2012 01:39 AM, Luiz Capitulino wrote:
> > 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.
> 
> 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.

> 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.

> 
> >
> >> +
> >> +    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,
> >
> 
>