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

[Luiz Capitulino <lcapitulino@redhat.com>]

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.

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).

> 
> 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",