Re: POSIX shared memory (shm_open)

There's some support for sharing memory segments in segattach(2) and
between unrelated processes with segment(3).

On Wed, 24 Apr 2019 at 16:23, Lassi Kortela <[email protected]> wrote:

> Hello,
>
> Can the POSIX shared memory API be emulated on Plan 9 with reasonable
> effort? I didn't find any mention of 'shm_open' in Plan 9 source.
>
> To recap, the API works as follows:
>
> - shm_open(path) to open or create an shm object, get a file descriptor
> - shm_unlink(path) to remove the shm object from the path namespace
> - ftruncate(fd) to actually allocate n bytes for the shm object
> - fstat(fd) returns the size of the object in the st_size field
> - mmap(fd) to get a pointer to use the shared memory
>
> The shm fd works like other Unix fds (can be sent to an unrelated
> process over a Unix-domain socket, persists over fork(), and can persist
> over exec() if the close-on-exec flag is cleared). The kernel garbage
> collects the shm object after the last fd pointing to it is closed.
>
> I made the shim <https://github.com/lassik/shm_open_anon> to provide a
> "shm_open() without a pathname" on various Unix flavors. I'm wondering
> if Plan 9 support could be easily added.
>
> I should mention that I have never used Plan 9, just read some of the
> source and documentation.
>
> Regards,
> Lassi
>
>