Capabilities will be shared among collection of threads. A pager
will have a right to share its own capabilities with its space,
its thread group and its container.
Currently sharing is possible with only all of the caps. Next,
it will be support for cap splitting, granting, and partial sharing
and granting.
Added support for pagers that fault to suspend and become zombies
along with all the threads that they manage. Zombie killing is to
be done at a later time, from this special zombie queue.
The implementation works same as a suspension, with the added action
that the thread is moved to a queue in kernel container.
Issues:
- A page-faulting thread suspends if receives -1 from pager page fault ipc.
This is fine if pager is about to delete the thread, but it is not if
it is a buggy pager.
- Need to find a way to completely get rid of suspended pager.
- A method of deleting suspended tasks could remedy both cases above.
Removed dependency on hard-coded pager id. Pager id is now passed
as an environment string `pagerid' to tasks. Alternatively, this
could take space in the utcb of each task.
Any thread that touches a utcb inside the kernel now properly checks
whether the utcb is mapped on its owner, and whether the mapped physical
address matches that of the current thread's tables. If not the tables
are updated.
This way, even though page tables become incoherent on utcb address
change situations (such as fork() exit(), execve()) they get updated
as they are referenced.
Since mappings are added only conditionally, caches are flushed only
when an update is necessary.
Added UTCB functions for full ipc that copy buffer or string payloads
in secondary message registers.
Some posix syscalls now use these utcb functions to copy pathnames.
It makes more sense to have a scheduler (or runqueue pair) per-cpu
rather than per-container. This provides more flexible global scheduling
policy that is also simpler due to all scheduling details being controlled
from a single point.
Status:
- Capability initialization is a bit hacky with dummy current etc.
- All container caps belong to the pager
- Tasks refer to their pager's capabilities for mutex allocation - Hacky.
- Kernel container keeps quantitative caps and memory caps in separate lists - Hacky.
These will all evolve and get fixed.
- removed (%d) Sleeping print from contended kernel mutexes.
- removed (%d) Waiting print from WAIT_EVENT used by the pager for suspending tasks.
- removed prints from the mutex_control syscall and user mutex test.
- Fixed a wrong instruction in mutex.S user library
- Added support for blocking lock/unlock
- Divided waiting into wait_on_prepare and wait_on_prepared_wait
so that mutex_control lock is released after getting in the waitqueue.
- Declaring waitqueue on the stack should be done outside wait_on_prepare
Issues:
- Tests can be simplified for atomic data access instead of producer/consumer.
- kmalloc variable sized memory caches are not freed properly. Currently only the
last slot can be freed, occupied correctly. it should be done in any slot, i.e.
1, 2, 3, 4 instead of just 5.
- Need to add a mutex to kmalloc.
- Mutex test added. Forked tasks demonstrate produce/consumer using a
shared mmap'ed page.
- Added l4lib assembler syscall
- Added forgotten SWI to mutex control offset in syscall page.
- Added mutex head initialization
- Contended child successfully sleeps in a waitqueue.
Issues:
- Somehow the child's produced page buffer is altered at about [4020] offset.
Parent fails to validate buffer therefore.
- Need to add syncing to test so that parent does not unlock and lock again
before child has a chance to lock buffer and produce.
- Compiles and Codezero runs as normal without touching mutex implementation
- Mutex implementation needs testing.
The mutex control syscall allows userspace programs to declare any virtual
address as a mutex lock and ask for help from the kernel syscall
for resolving locking contentions.
Previously during ipc copy, only the currently active task flags were
checked. This means the flags of whoever doing the actual copy was used
in the ipc. Now flags are stored in the ktcb and checked by the copy routine.
Current use of the flags is to determine short/full/extended ipc.
Benefits & Facts:
- Messages up to 2 kilobytes may be sent.
- Both parties may use non-disjoint user buffers. E.g. any userspace address.
- Userspace buffers can page fault.
- Page faults punish timeslice of only the faulting thread.
- Any number of extended ipcs can take place at any one time, since
only ktcbs of ipc parties are engaged. No global buffer is used.
- This also provides smp-safety benefit.
Disadvantages:
- There is triple copying penalty. This has to be done:
- Sender buffer to sender ktcb
- Sender ktcb to receiver ktcb
- Receiver ktcb to receiver buffer.
This is due to the fact that buffers can be on non-disjoint userspace addresses.
If you want to avoid disadvantages and lose some of the benefits,
(e.g. address freedom, shorter copy size) use FULL IPC.
