If the application passes in IORING_FILE_INDEX_ALLOC as the file_slot,
then that's a hint to allocate a fixed file descriptor rather than have
one be passed in directly.
This can be useful for having io_uring manage the direct descriptor space.
Normal open direct requests will complete with 0 for success, and < 0
in case of error. If io_uring is asked to allocated the direct descriptor,
then the direct descriptor is returned in case of success.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/io_uring.c | 32 +++++++++++++++++++++++++++++---
include/uapi/linux/io_uring.h | 9 +++++++++
2 files changed, 38 insertions(+), 3 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 8c40411a7e78..ef999d0e09de 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4697,7 +4697,7 @@ static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
return __io_openat_prep(req, sqe);
}
-static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
+static int io_file_bitmap_get(struct io_ring_ctx *ctx)
{
struct io_file_table *table = &ctx->file_table;
unsigned long nr = ctx->nr_user_files;
@@ -4722,6 +4722,32 @@ static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
return -ENFILE;
}
+static int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags,
+ struct file *file, unsigned int file_slot)
+{
+ int alloc_slot = file_slot == IORING_FILE_INDEX_ALLOC;
+ struct io_ring_ctx *ctx = req->ctx;
+ int ret;
+
+ if (alloc_slot) {
+ io_ring_submit_lock(ctx, issue_flags);
+ file_slot = io_file_bitmap_get(ctx);
+ if (unlikely(file_slot < 0)) {
+ io_ring_submit_unlock(ctx, issue_flags);
+ return file_slot;
+ }
+ }
+
+ ret = io_install_fixed_file(req, file, issue_flags, file_slot);
+ if (alloc_slot) {
+ io_ring_submit_unlock(ctx, issue_flags);
+ if (!ret)
+ return file_slot;
+ }
+
+ return ret;
+}
+
static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
{
struct open_flags op;
@@ -4777,8 +4803,8 @@ static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
if (!fixed)
fd_install(ret, file);
else
- ret = io_install_fixed_file(req, file, issue_flags,
- req->open.file_slot - 1);
+ ret = io_fixed_fd_install(req, issue_flags, file,
+ req->open.file_slot);
err:
putname(req->open.filename);
req->flags &= ~REQ_F_NEED_CLEANUP;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 06621a278cb6..b7f02a55032a 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -63,6 +63,15 @@ struct io_uring_sqe {
__u64 __pad2[2];
};
+/*
+ * If sqe->file_index is set to this for opcodes that instantiate a new
+ * direct descriptor (like openat/openat2/accept), then io_uring will allocate
+ * an available direct descriptor instead of having the application pass one
+ * in. The picked direct descriptor will be returned in cqe->res, or -ENFILE
+ * if the space is full.
+ */
+#define IORING_FILE_INDEX_ALLOC (~0U)
+
enum {
IOSQE_FIXED_FILE_BIT,
IOSQE_IO_DRAIN_BIT,
--
2.35.1
