[PATCH v2 09/10] man/io_uring_register.2: document buffer registration updates

[Bijan Mottahedeh <bijan.mottahedeh@oracle.com>]

Document sparse buffer registrations and IORING_REGISER_BUFFER_UPDATE.

Signed-off-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
---
 man/io_uring_register.2 | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/man/io_uring_register.2 b/man/io_uring_register.2
index 225e461..5c7a39e 100644
--- a/man/io_uring_register.2
+++ b/man/io_uring_register.2
@@ -82,11 +82,13 @@ It is perfectly valid to setup a large buffer and then only use part
 of it for an I/O, as long as the range is within the originally mapped
 region.
 
-An application can increase or decrease the size or number of
-registered buffers by first unregistering the existing buffers, and
-then issuing a new call to
-.BR io_uring_register ()
-with the new buffers.
+The buffer set may be sparse, meaning that the
+.B iovec
+address and size fields in the array may be set to
+.B 0.
+See
+.B IORING_REGISTER_BUFFERS_UPDATE
+for how to update buffers in place.
 
 Note that registering buffers will wait for the ring to idle. If the application
 currently has requests in-flight, the registration will wait for those to
@@ -103,6 +105,20 @@ must be passed as NULL.  All previously registered buffers associated
 with the io_uring instance will be released. Available since 5.1.
 
 .TP
+.B IORING_REGISTER_BUFFERS_UPDATE
+This operation replaces existing iovecs in the registered buffer set with
+new ones, either turning a sparse entry (one where iovec base and len
+are equal to 0) into a real one, removing an existing entry (new one is
+set to 0), or replacing an existing entry with a new existing entry.
+.I arg
+must contain a pointer to a struct io_uring_rsrc_update, which contains
+an offset on which to start the update, and an array of iovecs to
+use for the update.
+.I nr_args
+must contain the number of iovecs in the passed in array. Available
+since 5.12.
+
+.TP
 .B IORING_REGISTER_FILES
 Register files for I/O.
 .I arg
@@ -152,6 +168,9 @@ use for the update.
 must contain the number of descriptors in the passed in array. Available
 since 5.5.
 
+Note that struct io_uring_files_update is deprecated since 5.12 and that
+io_uring_rsrc_update must be used instead.
+
 .TP
 .B IORING_UNREGISTER_FILES
 This operation requires no argument, and
-- 
1.8.3.1