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

[Corey Bryant]

On 06/13/2012 03:46 PM, Luiz Capitulino wrote:
> On Fri,  8 Jun 2012 11:42:57 -0400
> Corey Bryant <address@hidden> 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 (address@hidden)
> >   -Use passfd as command name (address@hidden)
> >
> > Signed-off-by: Corey Bryant <address@hidden>
> > ---
> >   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