Re: [seL4] Questions about Capability model

On 21 Sep 2016, at 3:29 , Daniel Wang wrote:

Hi all,

I’m new to the capability concept of seL4. Please correct me if I’m wrong. My understand of the capability is that it is a reference to a chunk of memory that allocated for specific purpose. Say if I want to do IPC between two threads A and B, I will need to apply an chunk of memory as endpoint, which give me a capability that I can pass from thread A to thread B is that correct? Also it is ok to assume the message passing mechanism in IPC is a producer-consumer model?

The reason I ask it because I’m thinking is it possible for three (or more) threads that need to communicate with each other using the same endpoint, or it has to be paired for each two of those threads to use an endpoint?

Caps are object references with implied access rights. They get produced by the kernel when some Untyped memory is retyped into a specific object type (eg a TCB or an array of endpoints). Not sure what you mean with producer-consumer. Anyone who holds a cap with send rights can send to the EP, anyone with a cap with receive rights can receive. There can be any number of senders or receivers. Gernot