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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
View File

@ -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)
*/

9
io_uring/opdef.c
View File

@ -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)

44
io_uring/openclose.c
View File

@ -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 @@ err:
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;
}

3
io_uring/openclose.h
View File

@ -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);