open/openat2: update man page to include IORING_FILE_INDEX_ALLOC

Signed-off-by: Jens Axboe <axboe@kernel.dk>

man/io_uring_prep_openat.3

diff --git a/man/io_uring_prep_openat.3 b/man/io_uring_prep_openat.3
index 8094619..b0f0946 100644
--- a/man/io_uring_prep_openat.3
+++ b/man/io_uring_prep_openat.3
@@ -67,6 +67,18 @@
 field, which is not a problem for liburing helpers, but users of the raw
 io_uring interface need to zero SQEs to avoid unexpected behavior.
 
+If
+.B IORING_FILE_INDEX_ALLOC
+is used as the
+.I file_index
+for a direct open, then io_uring will allocate a free direct descriptor in
+the existing table. The allocated descriptor is returned in the CQE
+.I res
+field just like it would be for a non-direct open request. If no more entries
+are available in the direct descriptor table,
+.B -ENFILE
+is returned instead.
+
 This function prepares an async
 .BR openat (2)
 request. See that man page for details.

man/io_uring_prep_openat2.3

diff --git a/man/io_uring_prep_openat2.3 b/man/io_uring_prep_openat2.3
index 4898e30..96682d8 100644
--- a/man/io_uring_prep_openat2.3
+++ b/man/io_uring_prep_openat2.3
@@ -67,6 +67,17 @@
 .I file_index
 field, which is not a problem for liburing helpers, but users of the raw
 io_uring interface need to zero SQEs to avoid unexpected behavior.
+If
+.B IORING_FILE_INDEX_ALLOC
+is used as the
+.I file_index
+for a direct open, then io_uring will allocate a free direct descriptor in
+the existing table. The allocated descriptor is returned in the CQE
+.I res
+field just like it would be for a non-direct open request. If no more entries
+are available in the direct descriptor table,
+.B -ENFILE
+is returned instead.
 
 This function prepares an async
 .BR openat2 (2)