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io_uring/openclose: add support for IORING_OP_FIXED_FD_INSTALL

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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@kernel.org>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe
2023-12-07 20:06:02 -07:00
parent 055c15626a
commit dc18b89ab1
4 changed files with 65 additions and 0 deletions
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9
include/uapi/linux/io_uring.h
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@@ -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)
*/