Subject: Re: detect IP/UDP destination address - msg#00033

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Re: detect IP/UDP destination address

On 12/18/06, Kieran Mansley <kieran-1e/NZYDlv+odnm+yROfE0A@xxxxxxxxxxxxxxxx> wrote: On Mon, 2006-12-18 at 10:54 +0100, beach.dk-Re5JQEeQqe8AvxtiuMwx3w@xxxxxxxxxxxxxxxx wrote: > Hi, > > I have set up an UDP-server using the raw API > > upcb= udp_new(); > udp_recv( upcb, callback_recv, get_nic_netif() ); > udp_bind( upcb, IP_ADDR_ANY, 1234 ); > > In my callback_recv function I can see the IP address of the UDP-client > so I can reply to it. > > But........ I would like to detect if the client sent the incoming UDP > packet using unicast or broadcast (so I can respond with a > corresponding unicats/broacast packet). > > Is this possible? Someone may correct me, as I'm not sure about this, but unicast/broadcast is a rather Ethernet specific concept, and so I'd be surprised if it was visible at the higher layers as these have to interoperate on many different physical networks. Kieran Maybe I was a bit careless with my vocabulary if unicast/broadcast is only related to the ethernet layer. It's the destination adress at the IP-layer (not ethernet layer) I'm interested in. /Beach/

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Race condition with lwip_select (and potential fix)

Hi all, I've been noticing occasional crashes within lwip when using select(). I think I've tracked the problem down to a race condition hidden in the interaction between lwip_select() and event_callback() (both in sockets.c). The failure case is as follows: User Thread: Calls lwip_select(): - Creates a select_cb on the stack. - Creates select_cb.sem. - Takes selectsem. - Inserts the select_cb into select_cb_list. - Releases selectsem. - Waits for select_cb.sem to be signalled (or timeout to expire). LwIP Thread: Data arrives, so calls event_callback(): - Takes selectsem. - select_cb_list is examined and scb stores a pointer to the select_cb. - Releases selectsem. User Thread: Timeout expires, so resumes execution of lwip_select(): - Takes selectsem. - Removes the select_cb from select_cb_list. - Releases selectsem. - Frees select_cb.sem. LwIP Thread: Resumes execution of event_callback(): - Tries to signal scb->sem, but select_cb and/or sem no longer exist. Based on the above analysis, the fix would appear to be to swap the order in which event_callback() signals the two semaphores. I've tried this and so far it appears to work. I'd appreciate any thoughts from other LwIP users though! Regards, Chris.

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Re: detect IP/UDP destination address

On 12/18/06, Kieran Mansley <kieran-1e/NZYDlv+odnm+yROfE0A@xxxxxxxxxxxxxxxx> wrote: On Mon, 2006-12-18 at 10:54 +0100, beach.dk-Re5JQEeQqe8AvxtiuMwx3w@xxxxxxxxxxxxxxxx wrote: > Hi, > > I have set up an UDP-server using the raw API > > upcb= udp_new(); > udp_recv( upcb, callback_recv, get_nic_netif() ); > udp_bind( upcb, IP_ADDR_ANY, 1234 ); > > In my callback_recv function I can see the IP address of the UDP-client > so I can reply to it. > > But........ I would like to detect if the client sent the incoming UDP > packet using unicast or broadcast (so I can respond with a > corresponding unicats/broacast packet). > > Is this possible? Someone may correct me, as I'm not sure about this, but unicast/broadcast is a rather Ethernet specific concept, and so I'd be surprised if it was visible at the higher layers as these have to interoperate on many different physical networks. Kieran Maybe I was a bit careless with my vocabulary if unicast/broadcast is only related to the ethernet layer. It's the destination adress at the IP-layer (not ethernet layer) I'm interested in. /Beach/

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Race condition with lwip_select (and potential fix)

Hi all, I've been noticing occasional crashes within lwip when using select(). I think I've tracked the problem down to a race condition hidden in the interaction between lwip_select() and event_callback() (both in sockets.c). The failure case is as follows: User Thread: Calls lwip_select(): - Creates a select_cb on the stack. - Creates select_cb.sem. - Takes selectsem. - Inserts the select_cb into select_cb_list. - Releases selectsem. - Waits for select_cb.sem to be signalled (or timeout to expire). LwIP Thread: Data arrives, so calls event_callback(): - Takes selectsem. - select_cb_list is examined and scb stores a pointer to the select_cb. - Releases selectsem. User Thread: Timeout expires, so resumes execution of lwip_select(): - Takes selectsem. - Removes the select_cb from select_cb_list. - Releases selectsem. - Frees select_cb.sem. LwIP Thread: Resumes execution of event_callback(): - Tries to signal scb->sem, but select_cb and/or sem no longer exist. Based on the above analysis, the fix would appear to be to swap the order in which event_callback() signals the two semaphores. I've tried this and so far it appears to work. I'd appreciate any thoughts from other LwIP users though! Regards, Chris.