Comment by king_geedorah
11 hours ago
io_uring supports submitting openat requests, which sounds like what you want. Open the dirfd, extract all the names via readdir and then submit openat SQEs all at once. Admittedly I have not used the io uring api myself so I can't speak to edge cases in doing so, but it's "on the happy path" as it were.
https://man7.org/linux/man-pages/man3/io_uring_prep_open.3.h...
https://man7.org/linux/man-pages/man2/readdir.2.html
Note that the prep open man page is a (3) page. You could of course construct the SQEs yourself.
You have a limit of 1k simultaneous open files per process - not sure what overhead exists in the kernel that made them impose this, but I guess it exists for a reason. You might run into trouble if you open too many files at ones (either the kernel kills your process, or you run into some internal kernel bottleneck that makes the whole endeavor not so worthwhile)
That's mainly for historical reasons (select syscall can only handle fds<1024), modern programs can just set their soft limit to their hard limit and not worry about it anymore: https://0pointer.net/blog/file-descriptor-limits.html