At the end I tried the pidfd_getfd syscall that is working really fine and giving me back a "clone" fd of an fd in that was opened from another process. I tested it opening a text file in the first process and after cloning the fd , I could really read the file also in the second process.Now the weird thing:1) In the first process I allocate- a huge page, then get the fd2) In the second process I get my "clone" fd and do an mmap, it works but if I write on that memory, the first process cannot see what I wroteint second_process(int remote_pid, int remote_mem_fd) {printf("remote_pid %d remote_mem_fd %d\n", remote_pid, remote_mem_fd);
int pidfd = syscall(__NR_pidfd_open, remote_pid, 0);
int my_mem_fd = syscall(438, pidfd, remote_mem_fd, 0);
printf("my_mem_fd %d\n", my_mem_fd); // This is nice
int flags = MAP_SHARED | MAP_HUGETLB | (30 << MAP_HUGE_SHIFT);
uint64_t* addr = (uint64_t*) mmap(NULL, 1024 * 1024 * 1024, PROT_READ|PROT_WRITE, flags, my_mem_fd, 0);
if (addr == -1)
perror("mmap");
*addr = 0x0101010102020202;}Il giorno gio 14 apr 2022 alle ore 21:51 Antonio Di Bacco <a.dibacco.ks@gmail.com> ha scritto:Il giorno gio 14 apr 2022 alle ore 21:01 Dmitry Kozlyuk <dmitry.kozliuk@gmail.com> ha scritto:2022-04-14 10:20 (UTC+0200), Antonio Di Bacco:
[...]
> Ok, after having a look to memif I managed to exchange the fd between the
> two processes and it works.
> Anyway the procedure seems a little bit clunky and I think I'm going to use
> the new SYSCALL pidfd_getfd
> to achieve the same result. In your opinion this method (getfd_pidfd)
> could also work if the two DPDK processes
> are inside different docker containers?
Honestly, I've just learned about pidfd_getfd() from you.
But I know that containers use PID namespaces, so there's a question
how you will obtain the pidfd of a process in another container.
In general, any method of sharing FD will work.
Remember that you also need offset and size.
Given that some channel is required to share those,
I think Unix domain socket is still the preferred way.
> Or is there another mechanims like using handles to hugepages present in
> the filesystem to share between two
> different containers?
FD is needed for mmap().
You need to either pass the FD or open() the same hugepage file by path.
I advise against using paths because they are not a part of DPDK API contract.Thank you very much Dmitry, your answers are always enlightening.I'm going to ask a different question on the dpdk.org about the best practice to share memory between two dpdk processes running in different containers.