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())
is seems to be a problem for SUID applications, which we like to
prevent as much as possible.
PR: docs/39530
Submitted by: Soren Spies <sspies at apple dot com>
MFC After: 3 days
a module was loaded might make the pathname inaccurate.
I wonder if an inode reference should be stored with the pathname
to allow a validity check?
Suggested by: rwatson@
for kldstat(2).
This allows libdtrace to determine the exact file from which
a kernel module was loaded without having to guess.
The kldstat(2) API is versioned with the size of the
kld_file_stat structure, so this change creates version 2.
Add the pathname to the verbose output of kldstat(8) too.
MFC: 3 days
call the pad-less versions of the corresponding syscalls if the running
kernel supports it. Check kern.osreldate once per program and cache the
result to select the appropriate syscall. This maintains userland
compatability with kernel.old's from quite a while back.
Approved by: re (kensmith)
syscalls, unless WITHOUT_SYSCALL_COMPAT is defined. The default case
will have the .c wrappers still. If you define WITHOUT_SYSCALL_COMPAT,
the .c wrappers will go away and libc will make direct syscalls.
After 7-stable starts, the direct syscall method will be default.
Approved by: re (kensmith)
Add IMPLEMENTATION NOTES section explaining in detail the effect this
system call has in common use cases involving PF_INET and PF_INET6 sockets.
PR: kern/84761
MFC after: 2 days
effective group ID (and any of our group) doesn't match the group ID of the
file, we get EPERM. This doesn't conform POSIX. POSIX requires that we should
return 0, but silently clear the set-gid bit.
- O_NONBLOCK flag has to be set, if it is not set, open(2) will wait for
another process opening the fifo for reading,
- Use O_WRONLY which implies that the file has to be opened _only_ for write.
