Re: [PATCH 1/1] tidbits: net-udp: solicit new client for server mode

Am 01.06.26 um 11:10 schrieb Philippe Gerum:
> Philippe Gerum <[email protected]> writes:
> 
>> Hannes Diethelm <[email protected]> writes:
>>
>>> This fixes random EINPROGRESS at init or during runtime.
>>>
>>> Also correct whitespaces and make stdout more consistent.
>>>
>>> Signed-off-by: Hannes Diethelm <[email protected]>
>>> ---
>>>   tidbits/oob-net-udp.c | 58 +++++++++++++++++++++++++++++++++++++------
>>>   1 file changed, 50 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/tidbits/oob-net-udp.c b/tidbits/oob-net-udp.c
>>> index 11b8459..7af834f 100644
>>> --- a/tidbits/oob-net-udp.c
>>> +++ b/tidbits/oob-net-udp.c
>>> @@ -50,12 +50,12 @@ static void usage(void)
>>>   }
>>>   
>>>   static void print_addr(char* text, struct sockaddr_in *addr){
>>> -    char ip_str[INET_ADDRSTRLEN+1];
>>> -    inet_ntop(AF_INET, &(addr->sin_addr), ip_str, sizeof(ip_str));
>>> -    evl_printf("%s--------\n", text);
>>> -    evl_printf("IP-Address: %s\n", ip_str);
>>> -    evl_printf("Port:       %d\n", ntohs(addr->sin_port));
>>> -    evl_printf("Family:     %d\n", addr->sin_family);
>>> +	char ip_str[INET_ADDRSTRLEN+1];
>>> +	inet_ntop(AF_INET, &(addr->sin_addr), ip_str, sizeof(ip_str));
>>> +	evl_printf("== %s\n", text);
>>> +	evl_printf("   ip-address: %s\n", ip_str);
>>> +	evl_printf("   port:       %d\n", ntohs(addr->sin_port));
>>> +	evl_printf("   family:     %d\n", addr->sin_family);
>>>   }
>>>   
>>>   static void sender(int s, const char *text, int mcount,
>>> @@ -226,6 +226,8 @@ static void client(int s, const char *text, int mcount,
>>>   	free(tbuf);
>>>   }
>>>   
>>> +#define SERVER_ADDR_LIST_SIZE 64
>>> +
>>>   static void server(int s, const char *text, int mcount,
>>>   		struct sockaddr_in *addr, int iter)
>>>   {
>>> @@ -236,6 +238,9 @@ static void server(int s, const char *text, int mcount,
>>>   	ssize_t ret;
>>>   	char *tbuf;
>>>   	char rbuf[16384];
>>> +	in_addr_t addr_list[SERVER_ADDR_LIST_SIZE]={};
>>                                                    ^ missing whitespaces
>>> +	size_t addr_list_fill=0;
>>> +	bool solicit_done;
>>>   
>>>   	tlen = (strlen(text) + 1) * mcount;
>>>   	tbuf = malloc(tlen);
>>> @@ -276,6 +281,39 @@ static void server(int s, const char *text, int mcount,
>>>   			evl_printf(" (TRUNCATED)");
>>>   		evl_printf(": %.*s\n", (int)ret, rbuf);
>>>   
>>> +		/*
>>> +		 * We need to call evl_net_solicit for each new
>>> +		 * client once before sending data. This will break
>>> +		 * realtime for the first response.
>>> +		 * If this is not done and the ARP address is not
>>> +		 * yet in cache or garbage-collected, oob_sendmsg
>>> +		 * will return EINPROGRESS on start or during runtime.
>>> +		 */
>>
>> We can happily send redundant solicit requests to the core, no need to
>> filter out cached addresses, evl_net_solicit() will do the right thing.
>>
> 
> Except that doing so would always demote the caller to the in-band
> stage, which may not be what you want. The fact that we'd need to
> maintain a cache in apps in order to figure out whether solicitation
> should be done shows a shortcoming in the core, users should not have to
> do this dance.
> 
> We should have an oob call for probing the route+arp caches with
> ipv4. I'll look into this asap.
> 

Yes, this is the reason I do it this way and print out a message if
this happens.

I think server mode with multiple clients in real time is not something you
can just easily do without careful considerations what happens when multiple
clients send a message at the same time or TDMA behind. My intent in this example
is mostly to show that it is possible.

A real application would need one of these options:
- A thread only for solicitation so the main thread doesn't get blocked
- evl_net_solicit() with a flag like MSG_DONTWAIT and then poll in the main loop if
   the client is ready
- Know the clients in advance
- A warm up phase during clients can connect
- ...

However, a way for probing and reading the arp would shurely help. It would also be
nice to have an "evl net" command to list the entry's. I tried the normal arp command
but it doesn't behave nicely with evl.

No hurry from my side, I have linuxcnc already running well with evl oob networking,
I only need client mode and i know the IP in advance, so all good there.

Sorry about the whitespace issues, switching between projects... I sent a patch v2. Feel
free to merge this already and I can create a separate patch when probing ARP is here
or wait and I create a patch v3.