io_uring can currently open/close regular files or fixed/direct descriptors. Or you can instantiate a fixed descriptor from a regular one, and then close the regular descriptor. But you currently can't turn a purely fixed/direct descriptor into a regular file descriptor. IORING_OP_FIXED_FD_INSTALL adds support for installing a direct descriptor into the normal file table, just like receiving a file descriptor or opening a new file would do. This is all nicely abstracted into receive_fd(), and hence adding support for this is truly trivial. Since direct descriptors are only usable within io_uring itself, it can be useful to turn them into real file descriptors if they ever need to be accessed via normal syscalls. This can either be a transitory thing, or just a permanent transition for a given direct descriptor. By default, new fds are installed with O_CLOEXEC set. The application can disable O_CLOEXEC by setting IORING_FIXED_FD_NO_CLOEXEC in the sqe->install_fd_flags member. Suggested-by: Christian Brauner <brauner@xxxxxxxxxx> Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> --- v2: - add reviewed/suggested-by - default to O_CLOEXEC - pull in vfs.misc to get new receive_fd() Also see expanded test case here: https://git.kernel.dk/cgit/liburing/tree/test/fd-install.c include/uapi/linux/io_uring.h | 9 +++++++ io_uring/opdef.c | 9 +++++++ io_uring/openclose.c | 46 +++++++++++++++++++++++++++++++++++ io_uring/openclose.h | 3 +++ 4 files changed, 67 insertions(+) diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h index f1c16f817742..db4b913e6b39 100644 --- a/include/uapi/linux/io_uring.h +++ b/include/uapi/linux/io_uring.h @@ -71,6 +71,7 @@ struct io_uring_sqe { __u32 uring_cmd_flags; __u32 waitid_flags; __u32 futex_flags; + __u32 install_fd_flags; }; __u64 user_data; /* data to be passed back at completion time */ /* pack this to avoid bogus arm OABI complaints */ @@ -253,6 +254,7 @@ enum io_uring_op { IORING_OP_FUTEX_WAIT, IORING_OP_FUTEX_WAKE, IORING_OP_FUTEX_WAITV, + IORING_OP_FIXED_FD_INSTALL, /* this goes last, obviously */ IORING_OP_LAST, @@ -386,6 +388,13 @@ enum { /* Pass through the flags from sqe->file_index to cqe->flags */ #define IORING_MSG_RING_FLAGS_PASS (1U << 1) +/* + * IORING_OP_FIXED_FD_INSTALL flags (sqe->install_fd_flags) + * + * IORING_FIXED_FD_NO_CLOEXEC Don't mark the fd as O_CLOEXEC + */ +#define IORING_FIXED_FD_NO_CLOEXEC (1U << 0) + /* * IO completion data structure (Completion Queue Entry) */ diff --git a/io_uring/opdef.c b/io_uring/opdef.c index 799db44283c7..6705634e5f52 100644 --- a/io_uring/opdef.c +++ b/io_uring/opdef.c @@ -469,6 +469,12 @@ const struct io_issue_def io_issue_defs[] = { .prep = io_eopnotsupp_prep, #endif }, + [IORING_OP_FIXED_FD_INSTALL] = { + .needs_file = 1, + .audit_skip = 1, + .prep = io_install_fixed_fd_prep, + .issue = io_install_fixed_fd, + }, }; const struct io_cold_def io_cold_defs[] = { @@ -704,6 +710,9 @@ const struct io_cold_def io_cold_defs[] = { [IORING_OP_FUTEX_WAITV] = { .name = "FUTEX_WAITV", }, + [IORING_OP_FIXED_FD_INSTALL] = { + .name = "FIXED_FD_INSTALL", + }, }; const char *io_uring_get_opcode(u8 opcode) diff --git a/io_uring/openclose.c b/io_uring/openclose.c index 74fc22461f48..20efb022563d 100644 --- a/io_uring/openclose.c +++ b/io_uring/openclose.c @@ -31,6 +31,11 @@ struct io_close { u32 file_slot; }; +struct io_fixed_install { + struct file *file; + unsigned int o_flags; +}; + static bool io_openat_force_async(struct io_open *open) { /* @@ -254,3 +259,44 @@ int io_close(struct io_kiocb *req, unsigned int issue_flags) io_req_set_res(req, ret, 0); return IOU_OK; } + +int io_install_fixed_fd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) +{ + struct io_fixed_install *ifi; + unsigned int flags; + + if (sqe->off || sqe->addr || sqe->len || sqe->buf_index || + sqe->splice_fd_in || sqe->addr3) + return -EINVAL; + + /* must be a fixed file */ + if (!(req->flags & REQ_F_FIXED_FILE)) + return -EBADF; + + ifi = io_kiocb_to_cmd(req, struct io_fixed_install); + + flags = READ_ONCE(sqe->install_fd_flags); + if (flags & ~IORING_FIXED_FD_NO_CLOEXEC) + return -EINVAL; + + /* default to O_CLOEXEC, disable if IORING_FIXED_FD_NO_CLOEXEC is set */ + if (flags & IORING_FIXED_FD_NO_CLOEXEC) + ifi->o_flags = 0; + else + ifi->o_flags = O_CLOEXEC; + + return 0; +} + +int io_install_fixed_fd(struct io_kiocb *req, unsigned int issue_flags) +{ + struct io_fixed_install *ifi; + int ret; + + ifi = io_kiocb_to_cmd(req, struct io_fixed_install); + ret = receive_fd(req->file, NULL, ifi->o_flags); + if (ret < 0) + req_set_fail(req); + io_req_set_res(req, ret, 0); + return IOU_OK; +} diff --git a/io_uring/openclose.h b/io_uring/openclose.h index 4b1c28d3a66c..8a93c98ad0ad 100644 --- a/io_uring/openclose.h +++ b/io_uring/openclose.h @@ -12,3 +12,6 @@ int io_openat2(struct io_kiocb *req, unsigned int issue_flags); int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe); int io_close(struct io_kiocb *req, unsigned int issue_flags); + +int io_install_fixed_fd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe); +int io_install_fixed_fd(struct io_kiocb *req, unsigned int issue_flags); -- 2.42.0 -- Jens Axboe
