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-----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRAhzRXHqcMeLMyaSiRxhvAZXjcogUCX4a4sAAKCRCRxhvAZXjc ohdRAP9fclgrRkTl3o4cgaK0PUMt8BZ5QCg/SPQrVT58AQlfSwEAsNtWAeo6U2z1 FLGuCoPBEW1Zghkj1lMbIhj5zyVaEQ8= =Z7Q0 -----END PGP SIGNATURE----- Merge tag 'threads-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux Pull pidfd updates from Christian Brauner: "This introduces a new extension to the pidfd_open() syscall. Users can now raise the new PIDFD_NONBLOCK flag to support non-blocking pidfd file descriptors. This has been requested for uses in async process management libraries such as async-pidfd in Rust. Ever since the introduction of pidfds and more advanced async io various programming languages such as Rust have grown support for async event libraries. These libraries are created to help build epoll-based event loops around file descriptors. A common pattern is to automatically make all file descriptors they manage to O_NONBLOCK. For such libraries the EAGAIN error code is treated specially. When a function is called that returns EAGAIN the function isn't called again until the event loop indicates the the file descriptor is ready. Supporting EAGAIN when waiting on pidfds makes such libraries just work with little effort. This introduces a new flag PIDFD_NONBLOCK that is equivalent to O_NONBLOCK. This follows the same patterns we have for other (anon inode) file descriptors such as EFD_NONBLOCK, IN_NONBLOCK, SFD_NONBLOCK, TFD_NONBLOCK and the same for close-on-exec flags. Passing a non-blocking pidfd to waitid() currently has no effect, i.e. is not supported. There are users which would like to use waitid() on pidfds that are O_NONBLOCK and mix it with pidfds that are blocking and both pass them to waitid(). The expected behavior is to have waitid() return -EAGAIN for non-blocking pidfds and to block for blocking pidfds without needing to perform any additional checks for flags set on the pidfd before passing it to waitid(). Non-blocking pidfds will return EAGAIN from waitid() when no child process is ready yet. Returning -EAGAIN for non-blocking pidfds makes it easier for event loops that handle EAGAIN specially. It also makes the API more consistent and uniform. In essence, waitid() is treated like a read on a non-blocking pidfd or a recvmsg() on a non-blocking socket. With the addition of support for non-blocking pidfds we support the same functionality that sockets do. For sockets() recvmsg() supports MSG_DONTWAIT for pidfds waitid() supports WNOHANG. Both flags are per-call options. In contrast non-blocking pidfds and non-blocking sockets are a setting on an open file description affecting all threads in the calling process as well as other processes that hold file descriptors referring to the same open file description. Both behaviors, per call and per open file description, have genuine use-cases. The interaction with the WNOHANG flag is documented as follows: - If a non-blocking pidfd is passed and WNOHANG is not raised we simply raise the WNOHANG flag internally. When do_wait() returns indicating that there are eligible child processes but none have exited yet we set EAGAIN. If no child process exists we continue returning ECHILD. - If a non-blocking pidfd is passed and WNOHANG is raised waitid() will continue returning 0, i.e. it will not set EAGAIN. This ensure backwards compatibility with applications passing WNOHANG explicitly with pidfds" * tag 'threads-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: tests: remove O_NONBLOCK before waiting for WSTOPPED tests: add waitid() tests for non-blocking pidfds tests: port pidfd_wait to kselftest harness pidfd: support PIDFD_NONBLOCK in pidfd_open() exit: support non-blocking pidfds |
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.. | ||
.gitignore | ||
config | ||
Makefile | ||
pidfd_fdinfo_test.c | ||
pidfd_getfd_test.c | ||
pidfd_open_test.c | ||
pidfd_poll_test.c | ||
pidfd_setns_test.c | ||
pidfd_test.c | ||
pidfd_wait.c | ||
pidfd.h |