Indirect IPC or direct IPC

Marcus Voelp voelp at
Wed Jan 10 09:12:18 CET 2007


chenggh wrote:
> Hi:
> 	Today I read the DICE Manual 3.1.0 and it talks about something about 
> indirect IPC and direct IPC.
> 	According to my understanding it seems like this:
> 	indirect IPC: sender - > message buffer -> receiver
> 	direct IPC: sender ->sender buffer -> receive buffer ->receiver.
I assume you refer to the sections on indirect parts IPC. In the L4.V2 
interface strings can be transmitted either directly or indirectly. In 
the direct transmission one string can be located immediately after the 
message descriptor. See the L4.V2 Ref Man in Section 2.2.4 on Messages. 
The first message contains a set of dwords (dword0, 1, ...). In 
addition, L4.V2 allows to copy strings in place. In this case 
descriptors (string dope) point to the string to be transmitted.

In L4.V4 data can only be transmitted in the UTCBs (up to 64 words) or 
as indirect strings referred to by String Items.

Best regards

Marcus Völp

Technische Universität Dresden
Department of Computer Science
Institute for System Architecture 

Tel: +49 (351) 463 38350
Fax: +49 (351) 463 38284

Email: voelp at

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