Prototype of the proposal I made at https://lore.kernel.org/io-uring/20200211223235.GA25104@localhost/ . See also the discussion at https://twitter.com/josh_triplett/status/1235004009502494721 . The first patch is independent of the other two; it allows reserving file descriptors below a certain minimum for userspace-selected fd allocation only. The second patch implements userspace-selected fd allocation for openat2, introducing a new O_SPECIFIC_FD flag and an fd field in struct open_how. In io_uring, this allows sequences like openat2/read/close without waiting for the openat2 to complete. Multiple such sequences can overlap, as long as each uses a distinct file descriptor. The third patch adds userspace-selected fd allocation to pipe2 as well. I did this partly as a demonstration of how simple it is to wire up O_SPECIFIC_FD support for a new fd-allocating system call, and partly in the hopes that this may make it more useful to wire up io_uring support for pipe2 in the future. Josh Triplett (3): fs: Support setting a minimum fd for "lowest available fd" allocation fs: openat2: Extend open_how to allow userspace-selected fds fs: pipe2: Support O_SPECIFIC_FD fs/fcntl.c | 2 +- fs/file.c | 62 ++++++++++++++++++++++++++++---- fs/io_uring.c | 2 +- fs/open.c | 6 ++-- fs/pipe.c | 15 +++++--- include/linux/fcntl.h | 5 +-- include/linux/fdtable.h | 1 + include/linux/file.h | 3 ++ include/uapi/asm-generic/fcntl.h | 4 +++ include/uapi/linux/openat2.h | 2 ++ include/uapi/linux/prctl.h | 4 +++ kernel/sys.c | 10 ++++++ 12 files changed, 100 insertions(+), 16 deletions(-) -- 2.25.1
