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

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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
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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;
}
/*