Re: [seL4] How to get a capability of a virtual address

The first process is special and gets certain capabilities from the kernel which are documented in the kernel specification and guide. See section 8.1 "Initial Thread's Environment" of http://sel4.systems/Docs/seL4-manual.pdf. After this point your OS can keep track of whichever capabilities it creates and assigns to other processes in whatever manner it chooses. On Fri, Oct 17, 2014 at 8:03 AM, Yuxin Ren wrote:

Hi Kevin,

First, thank you for your reply very much. But I cannot understand those very well. Generally speaking, how does the OS personality get and know all caps for its own? More accurate, take the init process for example(which I am focusing on), how does it know which cap it has? I think it has to resort to the kernel, as the init process is created by the kernel, and I assume the kernel will set up caps for it.

Thanks again. Yuxin

On Fri, Oct 17, 2014 at 1:36 AM, Kevin Elphinstone wrote:

...

In general, seL4 provides low-level mechanisms, not high-level abstractions.

The vm model and process model are high-level abstractions of an OS personality on seL4, and as such, the OS personality is expected to keep the information required to implement those abstractions.

So I would expect the OS personality running on seL4 to keep track of the frame caps used to create VM objects/address-spaces, which threads are in what processes, etc..

There are some libraries that ease building OS personalities, which are the ones you are using. Those libraries walk a thin line between helpful libraries to aid the construction of OS personalities, and largely defining the OS personality.

We make no claims as to the line striking the right balance, this is evolving over time, with tension pulling the line in either direction.

So if my understanding of the current support libraries is correct, what you’re after is part of the book-keeping you should be managing when creating your OS personality on seL4 – it is not provide by the libraries nor seL4.

- Kevin

From: Devel [mailto:devel-bounces@sel4.systems] On Behalf Of Yuxin Ren Sent: Friday, 17 October 2014 5:21 AM To: devel@sel4.systems Subject: [seL4] How to get a capability of a virtual address

Hi All,

In sel4, how can a process/thread get the capability of its virtual address?

I know there is function

vspace_get_cap(vspace_t *vspace, void *vaddr)

But how can I know the current vspace the process/thread is in?

Thank you very much.

Yuxin

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