RE: [lwip-devel] [task #6683] Document lwIPs thread safety requirements

[Pettinato, Jim]

Simon,

Yes, this can really work... and the NO_SYS with SYS_LIGHTWEIGHT_PROT is not 
limited to the DMA/pbuf_ref scenario you describe. I think most users of your 
scenario #2 are using the protection scheme for allocating pbufs from the pool 
upon receiving an incoming packet interrupt... (you're right though, the 
ethernet driver ISR can only set a flag to inform a task-level routine there 
are packet(s) to process/pass to netif_input). It is very efficient though for 
the ISR reciever and the stack to share a buffer pool.

AFAIK, this is how the stack was designed to work originally (I'm sure Adam can 
expound on his original architecture if he still peeks in here at all)... 
Multitasking OS support was added later on in the development.

Speaking of uIP and lwIP's origins, I was waxing nostalgic and poking through 
some of the original uIP project code and rediscovered the uIP support for DNS 
client functionality  (resolv.c;.h). Don't suppose anyone knows why this didn't 
get ported to lwIP? (Or if it has, where I can find it? ;))

Jim



-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Simon Goldschmidt
Sent: Monday, April 16, 2007 11:33 AM
To: Kieran Mansley; Jonathan Larmour; Simon Goldschmidt; Frédéric Bernon; 
address@hidden
Subject: [lwip-devel] [task #6683] Document lwIPs thread safety requirements



Follow-up Comment #9, task #6683 (project lwip):

Forgot to say in the last comment:
I think it should be well documented that lwIP is designed to work when 
receiving packets from interrupt context but that the OS layer must support 
this!

re my own comment #6:
>First, there are 3 different scenarios:

regarding scenario 2):
>Raw-API only (NO_SYS=1), network interfaces work with interrupts

Can this really work? netif->input may not be called from interrupt context, 
since this might re.enter functions which are not re-entrant (tcp!). So the 
only thing we can do would be freeing pbufs after sending (e.g. with a 
DMA-ethernetif that calls pbuf_ref() before sending).

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