Add a new file descriptor type for IPC shared memory objects and use it to

implement shm_open(2) and shm_unlink(2) in the kernel:
- Each shared memory file descriptor is associated with a swap-backed vm
  object which provides the backing store.  Each descriptor starts off with
  a size of zero, but the size can be altered via ftruncate(2).  The shared
  memory file descriptors also support fstat(2).  read(2), write(2),
  ioctl(2), select(2), poll(2), and kevent(2) are not supported on shared
  memory file descriptors.
- shm_open(2) and shm_unlink(2) are now implemented as system calls that
  manage shared memory file descriptors.  The virtual namespace that maps
  pathnames to shared memory file descriptors is implemented as a hash
  table where the hash key is generated via the 32-bit Fowler/Noll/Vo hash
  of the pathname.
- As an extension, the constant 'SHM_ANON' may be specified in place of the
  path argument to shm_open(2).  In this case, an unnamed shared memory
  file descriptor will be created similar to the IPC_PRIVATE key for
  shmget(2).  Note that the shared memory object can still be shared among
  processes by sharing the file descriptor via fork(2) or sendmsg(2), but
  it is unnamed.  This effectively serves to implement the getmemfd() idea
  bandied about the lists several times over the years.
- The backing store for shared memory file descriptors are garbage
  collected when they are not referenced by any open file descriptors or
  the shm_open(2) virtual namespace.

Submitted by:	dillon, peter (previous versions)
Submitted by:	rwatson (I based this on his version)
Reviewed by:	alc (suggested converting getmemfd() to shm_open())

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/kern/syscalls.master b/sys/kern/syscalls.master
index 9538e4f..e51d7b1 100644
--- a/sys/kern/syscalls.master
+++ b/sys/kern/syscalls.master
@@ -847,5 +847,8 @@
 479	AUE_TRUNCATE	STD	{ int truncate(char *path, off_t length); }
 480	AUE_FTRUNCATE	STD	{ int ftruncate(int fd, off_t length); }
 481	AUE_KILL	STD	{ int thr_kill2(pid_t pid, long id, int sig); }
+482	AUE_NULL	STD	{ int shm_open(const char *path, int flags, \
+				    mode_t mode); }
+483	AUE_NULL	STD	{ int shm_unlink(const char *path); }
 ; Please copy any additions and changes to the following compatability tables:
 ; sys/compat/freebsd32/syscalls.master