Re: [Qemu-devel] [PATCH v2 2/4] qapi: Add passfd QMP command

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

On 06/13/2012 03:46 PM, Luiz Capitulino wrote:
> On Fri,  8 Jun 2012 11:42:57 -0400
> Corey Bryant <coreyb@linux.vnet.ibm.com> wrote:
>
>> This patch adds the passfd QMP command using the QAPI framework.
>> Like the getfd command, it is used to pass a file descriptor via
>> SCM_RIGHTS.  However, the passfd command also returns the received
>> file descriptor, which is a difference in behavior from the getfd
>> command, which returns nothing.
>
> Let's call it pass-fd instead.

Sure, that works for me.

>
> Also, getfd automatically closes a fd if an existing fdname is passed again.
> I don't think this is a good behavior, I think pass-fd should fail instead
> (note that we can't fix getfd though).
>

I agree.  It makes sense to fail rather than blindly closing the 
existing fd.  It can be closed explicitly with closefd if the user wants 
it closed.

>>
>> The closefd command can be used to close a file descriptor that was
>> passed with the passfd command.
>>
>> v2:
>>   -Introduce new QMP command to pass/return fd (lcapitulino@redhat.com)
>>   -Use passfd as command name (berrange@redhat.com)
>>
>> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
>> ---
>>   monitor.c        |   14 ++++++++++----
>>   qapi-schema.json |   15 +++++++++++++++
>>   qmp-commands.hx  |   27 +++++++++++++++++++++++++++
>>   3 files changed, 52 insertions(+), 4 deletions(-)
>>
>> diff --git a/monitor.c b/monitor.c
>> index 4c53cb6..980a226 100644
>> --- a/monitor.c
>> +++ b/monitor.c
>> @@ -2182,7 +2182,7 @@ static void do_inject_mce(Monitor *mon, const QDict *qdict)
>>   }
>>   #endif
>>
>> -void qmp_getfd(const char *fdname, Error **errp)
>> +int64_t qmp_passfd(const char *fdname, Error **errp)
>>   {
>>       mon_fd_t *monfd;
>>       int fd;
>> @@ -2190,13 +2190,13 @@ void qmp_getfd(const char *fdname, Error **errp)
>>       fd = qemu_chr_fe_get_msgfd(cur_mon->chr);
>>       if (fd == -1) {
>>           error_set(errp, QERR_FD_NOT_SUPPLIED);
>> -        return;
>> +        return -1;
>>       }
>>
>>       if (qemu_isdigit(fdname[0])) {
>>           error_set(errp, QERR_INVALID_PARAMETER_VALUE, "fdname",
>>                     "a name not starting with a digit");
>> -        return;
>> +        return -1;
>>       }
>>
>>       QLIST_FOREACH(monfd, &cur_mon->fds, next) {
>> @@ -2206,7 +2206,7 @@ void qmp_getfd(const char *fdname, Error **errp)
>>
>>           close(monfd->fd);
>>           monfd->fd = fd;
>> -        return;
>> +        return fd;
>>       }
>>
>>       monfd = g_malloc0(sizeof(mon_fd_t));
>> @@ -2214,6 +2214,12 @@ void qmp_getfd(const char *fdname, Error **errp)
>>       monfd->fd = fd;
>>
>>       QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
>> +    return fd;
>> +}
>> +
>> +void qmp_getfd(const char *fdname, Error **errp)
>> +{
>> +    qmp_passfd(fdname, errp);
>>       return;
>>   }
>>
>> diff --git a/qapi-schema.json b/qapi-schema.json
>> index 6be1d90..15da1b8 100644
>> --- a/qapi-schema.json
>> +++ b/qapi-schema.json
>> @@ -1864,6 +1864,21 @@
>>   { 'command': 'netdev_del', 'data': {'id': 'str'} }
>>
>>   ##
>> +# @passfd:
>> +#
>> +# Pass a file descriptor via SCM rights and assign it a name
>> +#
>> +# @fdname: file descriptor name
>> +#
>> +# Returns: The QEMU file descriptor that was received
>> +#          If file descriptor was not received, FdNotSupplied
>> +#          If @fdname is not valid, InvalidParameterType
>> +#
>> +# Since: 1.2.0
>> +##
>> +{ 'command': 'passfd', 'data': {'fdname': 'str'}, 'returns': 'int' }
>> +
>> +##
>>   # @getfd:
>>   #
>>   # Receive a file descriptor via SCM rights and assign it a name
>> diff --git a/qmp-commands.hx b/qmp-commands.hx
>> index f8c0f68..338a0b3 100644
>> --- a/qmp-commands.hx
>> +++ b/qmp-commands.hx
>> @@ -869,6 +869,33 @@ Example:
>>   EQMP
>>
>>       {
>> +        .name       = "passfd",
>> +        .args_type  = "fdname:s",
>> +        .params     = "passfd name",
>> +        .help       = "pass a file descriptor via SCM rights and assign it a name",
>> +        .mhandler.cmd_new = qmp_marshal_input_passfd,
>> +    },
>> +
>> +SQMP
>> +passfd
>> +------
>> +
>> +Pass a file descriptor via SCM rights and assign it a name.
>> +
>> +Arguments:
>> +
>> +- "fdname": file descriptor name (json-string)
>> +
>> +Return a json-int with the QEMU file descriptor that was received.
>> +
>> +Example:
>> +
>> +-> { "execute": "passfd", "arguments": { "fdname": "fd1" } }
>> +<- { "return": 42 }
>> +
>> +EQMP
>> +
>> +    {
>>           .name       = "getfd",
>>           .args_type  = "fdname:s",
>>           .params     = "getfd name",
>

-- 
Regards,
Corey