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Subject[PATCH 1/4] io_uring: allow open directly into fixed fd table
Date
Instead of opening a file into a process's file table as usual and then
registering the fd within io_uring, we can skip the first step and place
it directly into io_uring's fixed file table. Add support for that for
both OPENAT opcodes.

The behaviour is controlled by setting sqe->file_index, where 0 implies
the old behaviour, and non-0 values is translated into index
(file_index-1). The field is u16, hence sets a limit on how many slots
it covers.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 75 ++++++++++++++++++++++++++++++-----
include/uapi/linux/io_uring.h | 2 +
2 files changed, 68 insertions(+), 9 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 599b11152505..17d2c0eb89dc 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1075,6 +1075,8 @@ static bool io_poll_remove_waitqs(struct io_kiocb *req);
static int io_req_prep_async(struct io_kiocb *req);

static void io_fallback_req_func(struct work_struct *unused);
+static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
+ unsigned int issue_flags);

static struct kmem_cache *req_cachep;

@@ -3745,11 +3747,10 @@ static int __io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe
const char __user *fname;
int ret;

- if (unlikely(sqe->ioprio || sqe->buf_index))
+ if (unlikely(sqe->ioprio))
return -EINVAL;
if (unlikely(req->flags & REQ_F_FIXED_FILE))
return -EBADF;
-
/* open.how should be already initialised */
if (!(req->open.how.flags & O_PATH) && force_o_largefile())
req->open.how.flags |= O_LARGEFILE;
@@ -3762,6 +3763,10 @@ static int __io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe
req->open.filename = NULL;
return ret;
}
+ req->buf_index = READ_ONCE(sqe->file_index);
+ if (req->buf_index && (req->open.how.flags & O_CLOEXEC))
+ return -EINVAL;
+
req->open.nofile = rlimit(RLIMIT_NOFILE);
req->flags |= REQ_F_NEED_CLEANUP;
return 0;
@@ -3804,8 +3809,8 @@ static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
{
struct open_flags op;
struct file *file;
- bool nonblock_set;
- bool resolve_nonblock;
+ bool resolve_nonblock, nonblock_set;
+ bool fixed = !!req->buf_index;
int ret;

ret = build_open_flags(&req->open.how, &op);
@@ -3824,9 +3829,11 @@ static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
op.open_flag |= O_NONBLOCK;
}

- ret = __get_unused_fd_flags(req->open.how.flags, req->open.nofile);
- if (ret < 0)
- goto err;
+ if (!fixed) {
+ ret = __get_unused_fd_flags(req->open.how.flags, req->open.nofile);
+ if (ret < 0)
+ goto err;
+ }

file = do_filp_open(req->open.dfd, req->open.filename, &op);
if (IS_ERR(file)) {
@@ -3835,7 +3842,8 @@ static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
* marginal gain for something that is now known to be a slower
* path. So just put it, and we'll get a new one when we retry.
*/
- put_unused_fd(ret);
+ if (!fixed)
+ put_unused_fd(ret);

ret = PTR_ERR(file);
/* only retry if RESOLVE_CACHED wasn't already set by application */
@@ -3848,7 +3856,11 @@ static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
if ((issue_flags & IO_URING_F_NONBLOCK) && !nonblock_set)
file->f_flags &= ~O_NONBLOCK;
fsnotify_open(file);
- fd_install(ret, file);
+
+ if (!fixed)
+ fd_install(ret, file);
+ else
+ ret = io_install_fixed_file(req, file, issue_flags);
err:
putname(req->open.filename);
req->flags &= ~REQ_F_NEED_CLEANUP;
@@ -7776,6 +7788,50 @@ static int io_sqe_file_register(struct io_ring_ctx *ctx, struct file *file,
#endif
}

+static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
+ unsigned int issue_flags)
+{
+ struct io_ring_ctx *ctx = req->ctx;
+ int i = req->buf_index - 1;
+ bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
+ struct io_fixed_file *file_slot;
+ int ret = -EBADF;
+
+ if (WARN_ON_ONCE(req->buf_index == 0))
+ goto err;
+
+ io_ring_submit_lock(ctx, !force_nonblock);
+ if (file->f_op == &io_uring_fops)
+ goto err;
+ ret = -ENXIO;
+ if (!ctx->file_data)
+ goto err;
+ ret = -EINVAL;
+ if (i > ctx->nr_user_files)
+ goto err;
+
+ i = array_index_nospec(i, ctx->nr_user_files);
+ file_slot = io_fixed_file_slot(&ctx->file_table, i);
+ ret = -EEXIST;
+ if (file_slot->file_ptr)
+ goto err;
+
+ *io_get_tag_slot(ctx->file_data, i) = 0;
+ io_fixed_file_set(file_slot, file);
+ ret = io_sqe_file_register(ctx, file, i);
+ if (ret) {
+ file_slot->file_ptr = 0;
+ goto err;
+ }
+
+ ret = 0;
+err:
+ io_ring_submit_unlock(ctx, !force_nonblock);
+ if (ret)
+ fput(file);
+ return ret;
+}
+
static int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
struct io_rsrc_node *node, void *rsrc)
{
@@ -10231,6 +10287,7 @@ static int __init io_uring_init(void)
BUILD_BUG_SQE_ELEM(32, __u64, user_data);
BUILD_BUG_SQE_ELEM(40, __u16, buf_index);
BUILD_BUG_SQE_ELEM(40, __u16, buf_group);
+ BUILD_BUG_SQE_ELEM(40, __u16, file_index);
BUILD_BUG_SQE_ELEM(42, __u16, personality);
BUILD_BUG_SQE_ELEM(44, __s32, splice_fd_in);

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 79126d5cd289..f105deb4da1d 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -52,6 +52,8 @@ struct io_uring_sqe {
__u16 buf_index;
/* for grouped buffer selection */
__u16 buf_group;
+ /* index into fixed files */
+ __u16 file_index;
} __attribute__((packed));
/* personality to use, if used */
__u16 personality;
--
2.32.0
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