Commit dc18b89a authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring/openclose: add support for IORING_OP_FIXED_FD_INSTALL 



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: default avatarChristian Brauner <brauner@kernel.org>
Reviewed-by: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 055c1562

include/uapi/linux/io_uring.h

+9 −0
Original line number Diff line number Diff line
@@ -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)

 */

io_uring/opdef.c

+9 −0
Original line number Diff line number Diff line
@@ -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)

io_uring/openclose.c

+44 −0
Original line number Diff line number Diff line
@@ -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 +259,42 @@ 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;



	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 */

	ifi = io_kiocb_to_cmd(req, struct io_fixed_install);

	ifi->o_flags = O_CLOEXEC;

	if (flags & IORING_FIXED_FD_NO_CLOEXEC)

		ifi->o_flags = 0;



	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;

}

io_uring/openclose.h

+3 −0
Original line number Diff line number Diff line
@@ -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);