mmap() with MAP_ANON | MAP_SHARED is used for creating shared
memory mappings that can be shared among a process and its descendants
(think fork())
Currently shmget/at creates shared virtual files on the fly and calls
do_mmap to create anonymous shared mappings. Now sys_mmap uses this
interface to create virtual files on the fly and call do_mmap on those
files.
In the future a common shared virtual file creation method should be
added and commonly used by both interfaces.
- 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.
Upon fork, child was created in a new space but as a copy of any
cloned thread in the parent space. This was due to the search of forker thread
by its space id (which is shared among many cloned threads).
Now fixed.
modified: src/api/thread.c
modified: tasks/mm0/src/task.c
- Test0 has a full ipc mr read/write test.
- A full ipc occurs for definite only if both parties use the FULL IPC flag.
Otherwise the thread that makes the ipc copy rules on whether it was a short
or a full copy.
- Added a full ipc send/recv test
- Removed non-zero value checking in r2 for ipc that was there
to catch inadvertent full ipc calls.
- Added correct hanlding for read/write mrs for current status of utcb.
TODO:
- Add mapping of every utcb to every task for privileged access so that
the kernel can access every utcb without switching spaces.
- Removal of same mappings
- Upon thread creation need to copy page tables accordingly i.e.
each task will have its own utcb mapped with USER access, but every
other utcb as kernel access only. Need to handle this case upon page
table copying.
- Added ARM register ipc usage explanation to glue/arm/message.h
- In the current design, the unused r2 register is a system register
that kernel checks for ipc flags such as:
- IPC type: e.g. full or extended.
- In extended IPC, MR index containing message buffer ptr.
- In extended IPC, message size
- During execve/map_stack when setting up the environment and argument stack,
the stack map size was in bytes instead of pfns.
- Can now execve 16 forked tasks with success.
- Only the topmost parent prints pass messages. Any failed child can print fail message.
- Added testing of 16 forked threads doing file create/read/write/close and
16 forked x 4 cloned = 64 threads spawning/exiting
- Proper releasing of user pmd and pgds when a space is not used.
- Proper releasing of task, space ids.
- At occasions a starting thread gets bogus SPSR, this needs investigating.
- At a very rare occasion arch_setup_new_thread() had a kernel data abort during
register copying from one task to another. Needs investigating.
- Fixed potential concurrency bugs due to preemption being enabled.
- Introduced a new address space structure to better account for
address spaces and page tables.
- Currently executes fine up to forking. Will investigate.
