These patches add support for IORING_OP_GETDENTS, which is a new io_uring opcode that more or less does an lseek(sqe->fd, sqe->off, SEEK_SET) followed by a getdents64(sqe->fd, (void *)sqe->addr, sqe->len). A dumb test program for IORING_OP_GETDENTS is available here: https://krautbox.wantstofly.org/~buytenh/uringfind-v2.c This test program does something along the lines of what find(1) does: it scans recursively through a directory tree and prints the names of all directories and files it encounters along the way -- but then using io_uring. (The io_uring version prints the names of encountered files and directories in an order that's determined by SQE completion order, which is somewhat nondeterministic and likely to differ between runs.) On a directory tree with 14-odd million files in it that's on a six-drive (spinning disk) btrfs raid, find(1) takes: # echo 3 > /proc/sys/vm/drop_caches # time find /mnt/repo > /dev/null real 24m7.815s user 0m15.015s sys 0m48.340s # And the io_uring version takes: # echo 3 > /proc/sys/vm/drop_caches # time ./uringfind /mnt/repo > /dev/null real 10m29.064s user 0m4.347s sys 0m1.677s # The fully cached case also shows some speedup. find(1): # time find /mnt/repo > /dev/null real 0m5.223s user 0m1.926s sys 0m3.268s # Versus the io_uring version: # time ./uringfind /mnt/repo > /dev/null real 0m3.604s user 0m2.417s sys 0m0.793s # That said, the point of this patch isn't primarily to enable lightning-fast find(1) or du(1), but more to complete the set of filesystem I/O primitives available via io_uring, so that applications can do all of their filesystem I/O using the same mechanism, without having to manually punt some of their work out to worker threads -- and indeed, an object storage backend server that I wrote a while ago can run with a pure io_uring based event loop with this patch. Changes since v2 RFC: - Rebase onto io_uring-2021-02-17 plus a manually applied version of the mkdirat patch. The latter is needed because userland (liburing) has already merged the opcode for IORING_OP_MKDIRAT (in commit "io_uring.h: 5.12 pending kernel sync") while this opcode isn't in the kernel yet (as of io_uring-2021-02-17), and this means that this can't be merged until IORING_OP_MKDIRAT is merged. - Adapt to changes made in "io_uring: replace force_nonblock with flags" that are in io_uring-2021-02-17. Changes since v1 RFC: - Drop the trailing '64' from IORING_OP_GETDENTS64 (suggested by Matthew Wilcox). - Instead of requiring that sqe->off be zero, use this field to pass in a directory offset to start reading from. For the first IORING_OP_GETDENTS call on a directory, this can be set to zero, and for subsequent calls, it can be set to the ->d_off field of the last struct linux_dirent64 returned by the previous call. Lennert Buytenhek (2): readdir: split the core of getdents64(2) out into vfs_getdents() io_uring: add support for IORING_OP_GETDENTS fs/io_uring.c | 73 ++++++++++++++++++++++++++++++++++++++++++ fs/readdir.c | 25 +++++++++----- include/linux/fs.h | 4 ++ include/uapi/linux/io_uring.h | 1 4 files changed, 95 insertions(+), 8 deletions(-)
