Re: [dpdk-dev] [PATCH v2 3/4] eal: add synchronous multi-process communication

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> 
> We need the synchronous way for multi-process communication,
> i.e., blockingly waiting for reply message when we send a request
> to the peer process.
> 
> We add two APIs rte_eal_mp_request() and rte_eal_mp_reply() for
> such use case. By invoking rte_eal_mp_request(), a request message
> is sent out, and then it waits there for a reply message. The
> timeout is hard-coded 5 Sec. And the replied message will be copied
> in the parameters of this API so that the caller can decide how
> to translate those information (including params and fds). Note
> if a primary process owns multiple secondary processes, this API
> will fail.
> 
> The API rte_eal_mp_reply() is always called by an mp action handler.
> Here we add another parameter for rte_eal_mp_t so that the action
> handler knows which peer address to reply.
> 
> We use mutex in rte_eal_mp_request() to guarantee that only one
> request is on the fly for one pair of processes.

You don't need to do things in such strange and restrictive way.
Instead you can do something like that:
1) Introduce new struct, list for it and mutex 
 struct sync_request {
      int reply_received;
      char dst[PATH_MAX];
      char reply[...];
      LIST_ENTRY(sync_request) next;
};

static struct  
    LIST_HEAD(list, sync_request);
    pthread_mutex_t lock;
   pthead_cond_t cond;
} sync_requests;

2) then at request() call:
  Grab sync_requests.lock
  Check do we already have a pending request for that destination,
  If yes - the release the lock and returns with error.
  - allocate and init new sync_request struct, set reply_received=0
  - do send_msg()
  -then in a cycle:
  pthread_cond_timed_wait(&sync_requests.cond, &sync_request.lock, &timespec);
  - at return from it check if sync_request.reply_received == 1, if not
check if timeout expired and either return a failure or go to the start of the cycle.

3) at mp_handler() if REPLY received - grab sync_request.lock, 
    search through sync_requests.list for dst[] ,
   if found, then set it's reply_received=1, copy the received message into reply
   and call pthread_cond_braodcast((&sync_requests.cond);
  
> 
> Suggested-by: Anatoly Burakov <anatoly.burakov@intel.com>
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
>  lib/librte_eal/common/eal_common_proc.c | 144 +++++++++++++++++++++++++++++---
>  lib/librte_eal/common/include/rte_eal.h |  73 +++++++++++++++-
>  lib/librte_eal/rte_eal_version.map      |   2 +
>  3 files changed, 206 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/librte_eal/common/eal_common_proc.c b/lib/librte_eal/common/eal_common_proc.c
> index 70519cc..f194a52 100644
> --- a/lib/librte_eal/common/eal_common_proc.c
> +++ b/lib/librte_eal/common/eal_common_proc.c
> @@ -32,6 +32,7 @@
>  static int mp_fd = -1;
>  static char *mp_sec_sockets[MAX_SECONDARY_PROCS];
>  static pthread_mutex_t mp_mutex_action = PTHREAD_MUTEX_INITIALIZER;
> +static pthread_mutex_t mp_mutex_request = PTHREAD_MUTEX_INITIALIZER;
> 
>  struct action_entry {
>  	TAILQ_ENTRY(action_entry) next;      /**< Next attached action entry */
> @@ -49,6 +50,10 @@ static struct action_entry_list action_entry_list =
> 
>  struct mp_msghdr {
>  	char action_name[MAX_ACTION_NAME_LEN];
> +#define MP_MSG	0 /* Share message with peers, will not block */
> +#define MP_REQ	1 /* Request for information, Will block for a reply */
> +#define MP_REP	2 /* Reply to previously-received request */

As a nit - please use enum {} instead for the above macros.


> +	int type;
>  	int fds_num;
>  	int len_params;
>  	char params[0];
> @@ -138,7 +143,8 @@ rte_eal_mp_action_unregister(const char *name)
>  }
> 
>  static int
> -read_msg(int fd, char *buf, int buflen, int *fds, int fds_num)
> +read_msg(int fd, char *buf, int buflen,
> +	 int *fds, int fds_num, struct sockaddr_un *s)
>  {
>  	int ret;
>  	struct iovec iov;
> @@ -151,6 +157,8 @@ read_msg(int fd, char *buf, int buflen, int *fds, int fds_num)
>  	iov.iov_base = buf;
>  	iov.iov_len  = buflen;
> 
> +	msgh.msg_name = s;
> +	msgh.msg_namelen = sizeof(*s);
>  	msgh.msg_iov = &iov;
>  	msgh.msg_iovlen = 1;
>  	msgh.msg_control = control;
> @@ -181,7 +189,7 @@ read_msg(int fd, char *buf, int buflen, int *fds, int fds_num)
>  }
> 
>  static int
> -process_msg(struct mp_msghdr *hdr, int len, int fds[])
> +process_msg(struct mp_msghdr *hdr, int len, int fds[], struct sockaddr_un *s)
>  {
>  	int ret;
>  	int params_len;
> @@ -199,10 +207,10 @@ process_msg(struct mp_msghdr *hdr, int len, int fds[])
>  	}
> 
>  	params_len = len - sizeof(struct mp_msghdr);
> -	ret = entry->action(hdr->params, params_len, fds, hdr->fds_num);
> +	ret = entry->action(hdr->params, params_len,
> +			    fds, hdr->fds_num, s->sun_path);
>  	pthread_mutex_unlock(&mp_mutex_action);
>  	return ret;
> -
>  }
> 
>  static void *
> @@ -211,11 +219,12 @@ mp_handle(void *arg __rte_unused)
>  	int len;
>  	int fds[SCM_MAX_FD];
>  	char buf[MAX_MSG_LENGTH];
> +	struct sockaddr_un sa;
> 
>  	while (1) {
> -		len = read_msg(mp_fd, buf, MAX_MSG_LENGTH, fds, SCM_MAX_FD);
> +		len = read_msg(mp_fd, buf, MAX_MSG_LENGTH, fds, SCM_MAX_FD, &sa);
>  		if (len > 0)
> -			process_msg((struct mp_msghdr *)buf, len, fds);
> +			process_msg((struct mp_msghdr *)buf, len, fds, &sa);
>  	}
> 
>  	return NULL;
> @@ -255,7 +264,8 @@ static int
>  mp_primary_proc(const void *params,
>  		int len __rte_unused,
>  		int fds[] __rte_unused,
> -		int fds_num __rte_unused)
> +		int fds_num __rte_unused,
> +		const void *peer __rte_unused)
>  {
>  	const struct proc_request *r = (const struct proc_request *)params;
> 
> @@ -362,7 +372,8 @@ rte_eal_mp_channel_init(void)
>  }
> 
>  static inline struct mp_msghdr *
> -format_msg(const char *act_name, const void *p, int len_params, int fds_num)
> +format_msg(const char *act_name, const void *p,
> +	   int len_params, int fds_num, int type)
>  {
>  	int len_msg;
>  	struct mp_msghdr *msg;
> @@ -384,6 +395,7 @@ format_msg(const char *act_name, const void *p, int len_params, int fds_num)
>  	strcpy(msg->action_name, act_name);
>  	msg->fds_num = fds_num;
>  	msg->len_params = len_params;
> +	msg->type = type;
>  	memcpy(msg->params, p, len_params);
>  	return msg;
>  }
> @@ -455,7 +467,9 @@ mp_send(const char *action_name,
>  	const void *params,
>  	int len_params,
>  	int fds[],
> -	int fds_num)
> +	int fds_num,
> +	int type,
> +	const void *peer)
>  {
>  	int i;
>  	int n = 0;
> @@ -468,7 +482,7 @@ mp_send(const char *action_name,
>  		return 0;
>  	}
> 
> -	msg = format_msg(action_name, params, len_params, fds_num);
> +	msg = format_msg(action_name, params, len_params, fds_num, type);
>  	if (msg == NULL)
>  		return 0;
> 
> @@ -477,6 +491,11 @@ mp_send(const char *action_name,
>  		return 0;
>  	}
> 
> +	if (peer) {
> +		n += send_msg(sockfd, peer, msg, fds);
> +		goto ret;
> +	}
> +
>  	if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
>  		/* broadcast to all secondaries */
>  		for (i = 0; i < MAX_SECONDARY_PROCS; ++i) {
> @@ -488,6 +507,7 @@ mp_send(const char *action_name,
>  	} else
>  		n += send_msg(sockfd, eal_mp_unix_path(), msg, fds);
> 
> +ret:
>  	free(msg);
>  	close(sockfd);
>  	return n;
> @@ -501,5 +521,107 @@ rte_eal_mp_sendmsg(const char *action_name,
>  		   int fds_num)
>  {
>  	RTE_LOG(DEBUG, EAL, "sendmsg: %s\n", action_name);
> -	return mp_send(action_name, params, len_params, fds, fds_num);
> +	return mp_send(action_name, params, len_params,
> +			fds, fds_num, MP_MSG, NULL);
> +}
> +
> +int
> +rte_eal_mp_request(const char *action_name,
> +		   void *params,
> +		   int len_p,
> +		   int fds[],
> +		   int fds_in,
> +		   int fds_out)
> +{
> +	int i, j;
> +	int sockfd;
> +	int nprocs;
> +	int ret = 0;
> +	struct mp_msghdr *req;
> +	struct timeval tv;
> +	char buf[MAX_MSG_LENGTH];
> +	struct mp_msghdr *hdr;
> +
> +	RTE_LOG(DEBUG, EAL, "request: %s\n", action_name);
> +
> +	if (fds_in > SCM_MAX_FD || fds_out > SCM_MAX_FD) {
> +		RTE_LOG(ERR, EAL, "Cannot send more than %d FDs\n", SCM_MAX_FD);
> +		rte_errno = -E2BIG;
> +		return 0;
> +	}
> +
> +	req = format_msg(action_name, params, len_p, fds_in, MP_REQ);
> +	if (req == NULL)
> +		return 0;
> +
> +	if ((sockfd = open_unix_fd(0)) < 0) {
> +		free(req);
> +		return 0;
> +	}
> +
> +	tv.tv_sec = 5;  /* 5 Secs Timeout */
> +	tv.tv_usec = 0;
> +	if (setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO,
> +			(const void *)&tv, sizeof(struct timeval)) < 0)
> +		RTE_LOG(INFO, EAL, "Failed to set recv timeout\n");
> +
> +	/* Only allow one req at a time */
> +	pthread_mutex_lock(&mp_mutex_request);
> +
> +	if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
> +		nprocs = 0;
> +		for (i = 0; i < MAX_SECONDARY_PROCS; ++i)
> +			if (!mp_sec_sockets[i]) {
> +				j = i;
> +				nprocs++;
> +			}
> +
> +		if (nprocs > 1) {
> +			RTE_LOG(ERR, EAL,
> +				"multi secondary processes not supported\n");
> +			goto free_and_ret;
> +		}
> +
> +		ret = send_msg(sockfd, mp_sec_sockets[j], req, fds);
> +	} else
> +		ret = send_msg(sockfd, eal_mp_unix_path(), req, fds);
> +
> +	if (ret == 0) {
> +		RTE_LOG(ERR, EAL, "failed to send request: %s\n", action_name);
> +		ret = -1;
> +		goto free_and_ret;
> +	}
> +
> +	ret = read_msg(sockfd, buf, MAX_MSG_LENGTH, fds, fds_out, NULL);
> +	if (ret > 0) {
> +		hdr = (struct mp_msghdr *)buf;
> +		if (hdr->len_params == len_p)
> +			memcpy(params, hdr->params, len_p);
> +		else {
> +			RTE_LOG(ERR, EAL, "invalid reply\n");
> +			ret = 0;
> +		}
> +	}
> +
> +free_and_ret:
> +	free(req);
> +	close(sockfd);
> +	pthread_mutex_unlock(&mp_mutex_request);
> +	return ret;
> +}
> +
> +int
> +rte_eal_mp_reply(const char *action_name,
> +		 const void *params,
> +		 int len_p,
> +		 int fds[],
> +		 int fds_in,
> +		 const void *peer)
> +{
> +	RTE_LOG(DEBUG, EAL, "reply: %s\n", action_name);
> +	if (peer == NULL) {
> +		RTE_LOG(ERR, EAL, "peer is not specified\n");
> +		return 0;
> +	}
> +	return mp_send(action_name, params, len_p, fds, fds_in, MP_REP, peer);
>  }
> diff --git a/lib/librte_eal/common/include/rte_eal.h b/lib/librte_eal/common/include/rte_eal.h
> index 9884c0b..2690a77 100644
> --- a/lib/librte_eal/common/include/rte_eal.h
> +++ b/lib/librte_eal/common/include/rte_eal.h
> @@ -192,7 +192,7 @@ int rte_eal_primary_proc_alive(const char *config_file_path);
>   * this function typedef to register action for coming messages.
>   */
>  typedef int (*rte_eal_mp_t)(const void *params, int len,
> -			    int fds[], int fds_num);
> +			    int fds[], int fds_num, const void *peer);
> 
>  /**
>   * Register an action function for primary/secondary communication.
> @@ -245,7 +245,7 @@ void rte_eal_mp_action_unregister(const char *name);
>   *   The fds argument is an array of fds sent with sendmsg.
>   *
>   * @param fds_num
> - *   The fds_num argument is number of fds to be sent with sendmsg.
> + *   The number of fds to be sent with sendmsg.
>   *
>   * @return
>   *  - Returns the number of messages being sent successfully.
> @@ -255,6 +255,75 @@ rte_eal_mp_sendmsg(const char *action_name, const void *params,
>  		   int len_params, int fds[], int fds_num);
> 
>  /**
> + * Send a request to the peer process and expect a reply.
> + *
> + * This function sends a request message to the peer process, and will
> + * block until receiving reply message from the peer process. Note:
> + * this does not work for the primary process sending requests to its
> + * multiple (>1) secondary processes.
> + *
> + * @param action_name
> + *   The action_name argument is used to identify which action will be used.
> + *
> + * @param params
> + *   The params argument contains the customized message; as the reply is
> + *   received, the replied params will be copied to this pointer.
> + *
> + * @param len_p
> + *   The length of the customized message.
> + *
> + * @param fds
> + *   The fds argument is an array of fds sent with sendmsg; as the reply
> + *   is received, the replied fds will be copied into this array.
> + *
> + * @param fds_in
> + *   The number of fds to be sent.
> + *
> + * @param fds_out
> + *   The number of fds to be received.
> + *
> + * @return
> + *  - (1) on success;
> + *  - (0) on sending request successfully but no valid reply received.
> + *  - (<0) on failing to sending request.
> + */
> +int
> +rte_eal_mp_request(const char *action_name, void *params,
> +		   int len_p, int fds[], int fds_in, int fds_out);
> +
> +/**
> + * Send a reply to the peer process.
> + *
> + * This function will send a reply message in response to a request message
> + * received previously.
> + *
> + * @param action_name
> + *   The action_name argument is used to identify which action will be used.
> + *
> + * @param params
> + *   The params argument contains the customized message.
> + *
> + * @param len_p
> + *   The length of the customized message.
> + *
> + * @param fds
> + *   The fds argument is an array of fds sent with sendmsg.
> + *
> + * @param fds_in
> + *   The number of fds to be sent with sendmsg.
> + *
> + * @param peer
> + *   The fds_num argument is number of fds to be sent with sendmsg.
> + *
> + * @return
> + *  - (1) on success;
> + *  - (0) on failure.
> + */
> +int
> +rte_eal_mp_reply(const char *action_name, const void *params,
> +		 int len_p, int fds[], int fds_in, const void *peer);
> +
> +/**
>   * Usage function typedef used by the application usage function.
>   *
>   * Use this function typedef to define and call rte_set_application_usage_hook()
> diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
> index 5dacde5..068ac0b 100644
> --- a/lib/librte_eal/rte_eal_version.map
> +++ b/lib/librte_eal/rte_eal_version.map
> @@ -243,5 +243,7 @@ DPDK_18.02 {
>  	rte_eal_mp_action_register;
>  	rte_eal_mp_action_unregister;
>  	rte_eal_mp_sendmsg;
> +	rte_eal_mp_request;
> +	rte_eal_mp_reply;
> 
>  } DPDK_17.11;
> --
> 2.7.4