On Thu, Jul 9, 2020 at 9:24 AM Gedare Bloom <ged...@rtems.org> wrote: > > On Wed, Jul 8, 2020 at 10:08 PM Utkarsh Rai <utkarsh.ra...@gmail.com> wrote: > > > > > > > > > > On Wed, Jul 8, 2020 at 6:56 PM Gedare Bloom <ged...@rtems.org> wrote: > >> > >> On Wed, Jul 8, 2020 at 6:53 AM Sebastian Huber > >> <sebastian.hu...@embedded-brains.de> wrote: > >> > > >> > On 08/07/2020 14:43, Utkarsh Rai wrote: > >> > > >> > > Hello, > >> > > For my GSoC project, I have to provide high-level APIs for sharing > >> > > isolated stacks. > >> > > The POSIX compliant high-level way of sharing stacks can be to create > >> > > a shared memory object of the stack to be shared through shm_open and > >> > > then mmap that to the address space of the current stack. My doubt is, > >> > > shm_open() takes the path-name of the shared memory object. Since this > >> > > is a high-level API, how does the user 'convert' the stack address to > >> > > a shared memory object name? > >> > Do we need any POSIX compatibility for this? What would you do in a > >> > POSIX environment? You first get some memory, then hand it over to > >> > shm_open() to get a file descriptor, then use the file descriptor in > >> > mmap(), then use this for pthread_attr_setstack() and whatever? > >> > >> Yes, but the way to name objects is not set by posix. > >> > >> We need to provide our own way of translating an address into a name. > >> > >> > > > >> > > Dr.Gedare mentioned that one way to deal with naming would be > >> > > something like Mr.Sebastian has been doing with specifications. From > >> > > what I could gather, it is a hierarchical way of representing > >> > > objects(Though, I am not very sure if I understand this accurately). > >> > > How can something like this be implemented for naming stack-addresses? > >> > I am not sure if the specification of RTEMS is helpful in this context. > >> > >> I should have provided a little bit more guidance. I was thinking out > >> loud in yesterday's IRC meeting. My thought was more along the lines > >> of looking at how UIDs/naming should be done, and that specs had to > >> solve a naming problem. However the static nature of specs is not a > >> great fit to this problem. > >> > >> Actually, what is a good model would be something like /proc or > >> Linux's sysfs. An IMFS filesystem that exports task information could > >> be used to name memory regions. (It could eventually supplant > >> task-based statistics reporting too.) > >> > >> Another idea I had though, which seems to have been lost in the > >> shuffle, is to look at how the object names work in RTEMS and see if > >> we can add some fixed relationships, e.g., task_name # stack. > >> > >> I think we should start by just treating the entire task stack as a > >> single named object; either it is all shared, or none of it is shared. > >> This will be easier to implement and also more widely supported by > >> simpler MPU/MMU hardware. Later on, we can consider extending the > >> namespace with 'offsets' /taskfs/IDLE/stack/00000A28 > >> could be a location at byte A28 offset from the start of the stack of > >> the IDLE task. > >> > > > > I have a few questions - > > > > > Users would get the stack address of the stack they want to share through > > > pthread_attr_getstack(). Now, when they get the address they want to > > > share, they would pass the appropriate name of this memory-region. What > > > we have to provide is a mechanism to 'convert' this address to an > > > appropriate name. Is this the accepted way or the other way round, i.e. > > > the user passes a name as per a specified convention, and that name is > > > 'converted' to a specific address? > > > We may want both to work. You definitely want to have the > address->name working though, at the very least with the base address > returned by pthread_attr_getstack, but you might also want to be able > to map any address in a task's stack to the stack's "name". I'm not > sure if that is needed yet, but keep it in mind as a possible > extension later to use an address interval instead of a fixed base > address. >
One more clarification, the "name to address" conversion should be done within the shm+mmap implementation. shm takes a name and returns a fd, mmap takes an fd and returns an address. > > > When you say "treating the entire task stack as a single named object" > > > does it mean that we assign a single name, say "task_stack" to the > > > complete stack address space? In that case, how do we deal we the > > > presence of multiple tasks that are allocated from the same pool of task > > > stack? I understand that on a simpler MPU/MMU hardware it would make > > > sense to specify names for each memory section (.txt- "text", .bss - > > > "bss" etc.) but in this case, where we are sharing only selected > > > thread-stacks, I suppose we will have to have a way to handle 'offsets' > > > right from the start? > > > > No, I'm thinking one name for each task's stack. If you have 10 tasks, > you'd have 10 names. > > Each allocated task stack is logically a separate region within the > pool. For simple MPU hardware, it may not be possible to share > arbitrary task stacks, but in that case the implementation can just > ignore the name and share the entire pool if that is preferred, or > return an error. (The behavior could be configurable, maybe.) > > >> > >> Gedare _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
