Questions about Capability model
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? Thanks -Dan
On 21 Sep 2016, at 3:29 , Daniel Wang <danielwang.ksu@gmail.com> 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
Thank you for your quick response. by producer-consumer I mean if a message is sent to an EP and is received by another thread, is it gonna be consumed? Is there a way to send broadcast message to multiple receiver to the same EP? Thanks -Dan
On Sep 20, 2016, at 6:46 PM, Gernot.Heiser@data61.csiro.au wrote:
On 21 Sep 2016, at 3:29 , Daniel Wang <danielwang.ksu@gmail.com> 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 _______________________________________________ Devel mailing list Devel@sel4.systems https://sel4.systems/lists/listinfo/devel
On 21 Sep 2016, at 9:07 , Daniel Wang <danielwang.ksu@gmail.com> wrote:
Thank you for your quick response. by producer-consumer I mean if a message is sent to an EP and is received by another thread, is it gonna be consumed? Is there a way to send broadcast message to multiple receiver to the same EP?
the IPC model is rendez-vous, synchronous message transfer. Broadcast a higher-level abstraction that has no place in a minimal microkernel. See also https://www.cse.unsw.edu.au/~cs9242/16/lectures/01-intro.pdf Gernot
On 21.09.2016, at 09:16, Gernot.Heiser@data61.csiro.au wrote:
On 21 Sep 2016, at 9:07 , Daniel Wang <danielwang.ksu@gmail.com> wrote:
Thank you for your quick response. by producer-consumer I mean if a message is sent to an EP and is received by another thread, is it gonna be consumed? Is there a way to send broadcast message to multiple receiver to the same EP?
the IPC model is rendez-vous, synchronous message transfer. Broadcast a higher-level abstraction that has no place in a minimal microkernel. See also https://www.cse.unsw.edu.au/~cs9242/16/lectures/01-intro.pdf
What Gernot is saying in charming ways ;-) is that yes, it is consumed, that broadcast can be implemented on top of the existing mechanisms, and that it is therefore not inside the kernel (for the reasons in the slides). Depending on the requirements of your system, shared memory + notifications might make sense to implement broadcast without copying, or if messages are tiny, maybe some other combination. Cheers, Gerwin
participants (3)
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Daniel Wang -
Gernot.Heiser＠data61.csiro.au -
Gerwin.Klein＠data61.csiro.au