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io_uring: Add io_uring_setup flag to pre-register ring fd and never install it 

With IORING_REGISTER_USE_REGISTERED_RING, an application can register
the ring fd and use it via registered index rather than installed fd.
This allows using a registered ring for everything *except* the initial
mmap.

With IORING_SETUP_NO_MMAP, io_uring_setup uses buffers allocated by the
user, rather than requiring a subsequent mmap.

The combination of the two allows a user to operate *entirely* via a
registered ring fd, making it unnecessary to ever install the fd in the
first place. So, add a flag IORING_SETUP_REGISTERED_FD_ONLY to make
io_uring_setup register the fd and return a registered index, without
installing the fd.

This allows an application to avoid touching the fd table at all, and
allows a library to never even momentarily install a file descriptor.

This splits out an io_ring_add_registered_file helper from
io_ring_add_registered_fd, for use by io_uring_setup.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Link: https://lore.kernel.org/r/bc8f431bada371c183b95a83399628b605e978a3.1682699803.git.josh@joshtriplett.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Josh Triplett 2023-04-29 01:40:30 +09:00 committed by Jens Axboe
parent 03d89a2de2
commit 6e76ac5958
4 changed files with 57 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/uapi/linux/io_uring.h
View File

@ -178,6 +178,13 @@ enum {
*/
#define IORING_SETUP_NO_MMAP (1U << 14)
/*
* Register the ring fd in itself for use with
* IORING_REGISTER_USE_REGISTERED_RING; return a registered fd index rather
* than an fd.
*/
#define IORING_SETUP_REGISTERED_FD_ONLY (1U << 15)
enum io_uring_op {
IORING_OP_NOP,
IORING_OP_READV,

37
io_uring/io_uring.c
View File

@ -3788,19 +3788,13 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
return 0;
}
static int io_uring_install_fd(struct io_ring_ctx *ctx, struct file *file)
static int io_uring_install_fd(struct file *file)
{
int ret, fd;
int fd;
fd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
if (fd < 0)
return fd;
ret = __io_uring_add_tctx_node(ctx);
if (ret) {
put_unused_fd(fd);
return ret;
}
fd_install(fd, file);
return fd;
}
@ -3840,6 +3834,7 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
struct io_uring_params __user *params)
{
struct io_ring_ctx *ctx;
struct io_uring_task *tctx;
struct file *file;
int ret;
@ -3851,6 +3846,10 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
entries = IORING_MAX_ENTRIES;
}
if ((p->flags & IORING_SETUP_REGISTERED_FD_ONLY)
&& !(p->flags & IORING_SETUP_NO_MMAP))
return -EINVAL;
/*
* Use twice as many entries for the CQ ring. It's possible for the
* application to drive a higher depth than the size of the SQ ring,
@ -4007,22 +4006,30 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
goto err;
}
ret = __io_uring_add_tctx_node(ctx);
if (ret)
goto err_fput;
tctx = current->io_uring;
/*
* Install ring fd as the very last thing, so we don't risk someone
* having closed it before we finish setup
*/
ret = io_uring_install_fd(ctx, file);
if (ret < 0) {
/* fput will clean it up */
fput(file);
return ret;
}
if (p->flags & IORING_SETUP_REGISTERED_FD_ONLY)
ret = io_ring_add_registered_file(tctx, file, 0, IO_RINGFD_REG_MAX);
else
ret = io_uring_install_fd(file);
if (ret < 0)
goto err_fput;
trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags);
return ret;
err:
io_ring_ctx_wait_and_kill(ctx);
return ret;
err_fput:
fput(file);
return ret;
}
/*
@ -4049,7 +4056,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
IORING_SETUP_COOP_TASKRUN | IORING_SETUP_TASKRUN_FLAG |
IORING_SETUP_SQE128 | IORING_SETUP_CQE32 |
IORING_SETUP_SINGLE_ISSUER | IORING_SETUP_DEFER_TASKRUN |
IORING_SETUP_NO_MMAP))
IORING_SETUP_NO_MMAP | IORING_SETUP_REGISTERED_FD_ONLY))
return -EINVAL;
return io_uring_create(entries, &p, params);

3
io_uring/io_uring.h
View File

@ -75,6 +75,9 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd);
int io_uring_alloc_task_context(struct task_struct *task,
struct io_ring_ctx *ctx);
int io_ring_add_registered_file(struct io_uring_task *tctx, struct file *file,
int start, int end);
int io_poll_issue(struct io_kiocb *req, struct io_tw_state *ts);
int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr);
int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin);

41
io_uring/tctx.c
View File

@ -208,29 +208,38 @@ void io_uring_unreg_ringfd(void)
}
}
int io_ring_add_registered_file(struct io_uring_task *tctx, struct file *file,
int start, int end)
{
int offset;
for (offset = start; offset < end; offset++) {
offset = array_index_nospec(offset, IO_RINGFD_REG_MAX);
if (tctx->registered_rings[offset])
continue;
tctx->registered_rings[offset] = file;
return offset;
}
return -EBUSY;
}
static int io_ring_add_registered_fd(struct io_uring_task *tctx, int fd,
int start, int end)
{
struct file *file;
int offset;
for (offset = start; offset < end; offset++) {
offset = array_index_nospec(offset, IO_RINGFD_REG_MAX);
if (tctx->registered_rings[offset])
continue;
file = fget(fd);
if (!file) {
return -EBADF;
} else if (!io_is_uring_fops(file)) {
fput(file);
return -EOPNOTSUPP;
}
tctx->registered_rings[offset] = file;
return offset;
file = fget(fd);
if (!file) {
return -EBADF;
} else if (!io_is_uring_fops(file)) {
fput(file);
return -EOPNOTSUPP;
}
return -EBUSY;
offset = io_ring_add_registered_file(tctx, file, start, end);
if (offset < 0)
fput(file);
return offset;
}
/*