Implement POSIX Shared Memory Objects

[Gedare Bloom]

POSIX Shared Memory is a widely used API for inter-process communication. The functions in the API include:

• ​shm_open
• ​ftruncate
• ​mmap
• ​munmap
• ​shm_unlink
• ​close
• ​fstat
• ​fchown
• ​fchmod

[Gedare Bloom]

ba77628250ae7158db363fc0d7886ebd43e9cb69

[Sebastian Huber <sebastian.huber@…>]

In 7cb7454f9321f9d68ad79c7bc21458755a4a6b46/rtems:

psxtests: Relax shared memory tests

There is currently no proper mmap() implementation.

Update #2859.

[Gedare Bloom <gedare@…>]

In 87de70a2/rtems:

posix/mman: add mmap support for shm objects

Update #2859.

[Kevin Kirspel <kevin-kirspel@…>]

In 1549beb/rtems:

psxtests: Add a mmap dedicated test case

Updates #2859

[Sebastian Huber]

Test psxmmap01 fails with RTEMS_DEBUG:

*** BEGIN OF TEST PSX MMAP01 ***
Init: mmap - map at zero

Breakpoint 1, __assert_func (file=file@entry=0x2027fc8 "../../cpukit/../../../erc32/lib/include/rtems/score/chainimpl.h", line=line@entry=686, func=func@entry=0x2029198 <__func__.2359> "_Chain_Append_unprotected", failedexpr=failedexpr@entry=0x20286e0 "_Chain_Is_node_off_chain( the_node )") at ../../../../../../rtems/c/src/../../cpukit/libcsupport/src/__assert.c:37
37      {
(gdb) bt
#0  __assert_func (file=file@entry=0x2027fc8 "../../cpukit/../../../erc32/lib/include/rtems/score/chainimpl.h", line=line@entry=686, func=func@entry=0x2029198 <__func__.2359> "_Chain_Append_unprotected", failedexpr=failedexpr@entry=0x20286e0 "_Chain_Is_node_off_chain( the_node )") at ../../../../../../rtems/c/src/../../cpukit/libcsupport/src/__assert.c:37
#1  0x0200d688 in _Chain_Append_unprotected (the_node=0x2039450, the_chain=0x202f650 <mmap_mappings>) at ../../cpukit/../../../erc32/lib/include/rtems/score/chainimpl.h:686
#2  0x0200d720 in _Chain_Append_unprotected (the_node=0x2039450, the_chain=0x202f650 <mmap_mappings>) at ../../../../../../rtems/c/src/../../cpukit/sapi/src/chainprotected.c:74
#3  rtems_chain_append (chain=chain@entry=0x202f650 <mmap_mappings>, node=node@entry=0x2039450) at ../../../../../../rtems/c/src/../../cpukit/sapi/src/chainprotected.c:72
#4  0x0200a634 in mmap (addr=addr@entry=0xfffff000, len=len@entry=4096, prot=prot@entry=7, flags=<optimized out>, flags@entry=4114, fildes=fildes@entry=-1, off=<optimized out>) at ../../../../../../rtems/c/src/../../cpukit/posix/src/mmap.c:373
#5  0x020014cc in mmap_map_at_zero () at ../../../../../../../rtems/c/src/../../testsuites/psxtests/psxmmap01/init.c:100
#6  POSIX_Init (argument=<optimized out>) at ../../../../../../../rtems/c/src/../../testsuites/psxtests/psxmmap01/init.c:324
#7  0x0201be58 in _Thread_Entry_adaptor_pointer (executing=0x20318d8) at ../../../../../../rtems/c/src/../../cpukit/score/src/threadentryadaptorpointer.c:25
#8  0x0201bed4 in _Thread_Handler () at ../../../../../../rtems/c/src/../../cpukit/score/src/threadhandler.c:88
#9  0x0201be6c in _Thread_Handler () at ../../../../../../rtems/c/src/../../cpukit/score/src/threadhandler.c:38
(gdb) frame 3
#3  rtems_chain_append (chain=chain@entry=0x202f650 <mmap_mappings>, node=node@entry=0x2039450) at ../../../../../../rtems/c/src/../../cpukit/sapi/src/chainprotected.c:72
72        _Chain_Append_unprotected( chain, node );
(gdb) p *node
$1 = {
  next = 0x202f654 <mmap_mappings+4>, 
  previous = 0x202f650 <mmap_mappings>
}

[Kevin Kirspel <kevin-kirspel@…>]

In bb01a36/rtems:

Fixed issue with searching mapped addresses

The loop that checks if the current address is already mapped uses
the same local variable for the chanin node as the newly allocated
chain node so the allocated chain node gets over written.

Added a new local variable for the loop that checks the address

Updates #2859.

[Sebastian Huber <sebastian.huber@…>]

In b965f461/rtems:

posix: Use unprotected chain operations

Operarations are already protected by mmap_mappings_lock.

Updates #2859.

[Sebastian Huber]

The mmap_mappings_lock attributes don't create a mutex:

#define RTEMS_MUTEX_ATTRIBS \

(RTEMS_PRIORITY | RTEMS_SIMPLE_BINARY_SEMAPHORE | \

RTEMS_NO_INHERIT_PRIORITY | RTEMS_NO_PRIORITY_CEILING | RTEMS_LOCAL)

I suggest to use the libio mutex and keep the specialized lock/unlock functions. Mutex lock/unlock should not return a status code to simplify the error handling.

[Gedare Bloom <gedare@…>]

In b264998/rtems:

posix: replace mmap mappings lock with libio lock

Use the libio mutex lock instead of the mmap mappings lock.

Updates #2859.

[Gedare Bloom <gedare@…>]

In c6d897e5/rtems:

posix: fix warnings with mmap from heap/wkspace

Avoid void pointer arithmetic.

Updates #2859.

[Sebastian Huber <sebastian.huber@…>]

In 77cbb2a/rtems:

psxtests/psxmmap01: Fix warning

Update #2859.

[Gedare Bloom <gedare@…>]

In 1ab6d59/rtems-docs:

memory_management: update mmap, munmap, shm_open, shm_unlink

Close #2859.

[Gedare Bloom]

I consider this basically complete. Open new tickets against any bugs or added features.

[Sebastian Huber <sebastian.huber@…>]

In 694e946/rtems:

libio: Remove special-case reference count

The top-level IO library structures should contain no special-case data.

Update #2859.

[Sebastian Huber]

Milestone renamed