[dpdk-dev] [PATCH v6 1/2] eal: add channel for multi-process communication

[Tan, Jianfeng]

Hi Anatoly,

> -----Original Message-----
> From: Burakov, Anatoly
> Sent: Friday, January 26, 2018 6:26 PM
> To: Tan, Jianfeng; dev at dpdk.org
> Cc: Richardson, Bruce; Ananyev, Konstantin; thomas at monjalon.net
> Subject: Re: [PATCH v6 1/2] eal: add channel for multi-process
> communication
> 
> On 26-Jan-18 3:41 AM, Jianfeng Tan wrote:
> > Previouly, there are three channels for multi-process
> > (i.e., primary/secondary) communication.
> >    1. Config-file based channel, in which, the primary process writes
> >       info into a pre-defined config file, and the secondary process
> >       reads the info out.
> >    2. vfio submodule has its own channel based on unix socket for the
> >       secondary process to get container fd and group fd from the
> >       primary process.
> >    3. pdump submodule also has its own channel based on unix socket for
> >       packet dump.
> >
> > It'd be good to have a generic communication channel for multi-process
> > communication to accommodate the requirements including:
> >    a. Secondary wants to send info to primary, for example, secondary
> >       would like to send request (about some specific vdev to primary).
> >    b. Sending info at any time, instead of just initialization time.
> >    c. Share FDs with the other side, for vdev like vhost, related FDs
> >       (memory region, kick) should be shared.
> >    d. A send message request needs the other side to response immediately.
> >
> > This patch proposes to create a communication channel, based on
> datagram
> > unix socket, for above requirements. Each process will block on a unix
> > socket waiting for messages from the peers.
> >
> > Three new APIs are added:
> >
> >    1. rte_eal_mp_action_register() is used to register an action,
> >       indexed by a string, when a component at receiver side would like
> >       to response the messages from the peer processe.
> >    2. rte_eal_mp_action_unregister() is used to unregister the action
> >       if the calling component does not want to response the messages.
> >    3. rte_eal_mp_sendmsg() is used to send a message, and returns
> >       immediately. If there are n secondary processes, the primary
> >       process will send n messages.
> >
> > Suggested-by: Konstantin Ananyev <konstantin.ananyev at intel.com>
> > Signed-off-by: Jianfeng Tan <jianfeng.tan at intel.com>
> > Reviewed-by: Anatoly Burakov <anatoly.burakov at intel.com>
> > Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>
> > ---
> 
> <snip>
> 
> > +
> > +static int
> > +mp_send(struct rte_mp_msg *msg)
> > +{
> > +	int ret = 0;
> > +	DIR *mp_dir;
> > +	struct dirent *ent;
> > +
> > +	if (rte_eal_process_type() == RTE_PROC_SECONDARY) {
> > +		if (send_msg(eal_mp_socket_path(), msg) < 0)
> > +			return -1;
> > +		else
> > +			return 0;
> > +	}
> > +
> > +	/* broadcast to all secondary processes */
> > +	mp_dir = opendir(mp_dir_path);
> > +	if (!mp_dir) {
> > +		RTE_LOG(ERR, EAL, "Unable to open directory %s\n",
> > +				mp_dir_path);
> > +		rte_errno = errno;
> > +		return -1;
> > +	}
> > +	while ((ent = readdir(mp_dir))) {
> > +		if (fnmatch(mp_filter, ent->d_name, 0) != 0)
> > +			continue;
> > +
> > +		if (send_msg(ent->d_name, msg) < 0)
> > +			ret = -1;

Here ret is assigned to -1.

> > +	}
> > +	closedir(mp_dir);
> > +
> > +	return ret;
> 
> Nitpick: you probably don't need ret here, just return 0 as in other places.

We cannot just return 0 as it could be -1 as above comment shows.
The ret variable was introduced to avoid two "closedir()".

Thanks,
Jianfeng