io_uring: Add skip option for __io_sqe_files_update

This patch adds support for skipping a file descriptor when using
IORING_REGISTER_FILES_UPDATE.  __io_sqe_files_update will skip fds set
to IORING_REGISTER_FILES_SKIP. IORING_REGISTER_FILES_SKIP is inturn
added as a #define in io_uring.h
Signed-off-by: noah <goldstein.w.n@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8038,6 +8038,9 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 			err = -EFAULT;
 			break;
 		}
+		if (fd == IORING_REGISTER_FILES_SKIP)
+			continue;
+
 		i = array_index_nospec(up->offset + done, ctx->nr_user_files);
 		table = &ctx->file_data->table[i >> IORING_FILE_TABLE_SHIFT];
 		index = i & IORING_FILE_TABLE_MASK;

include/uapi/linux/io_uring.h

@@ -298,6 +298,9 @@ struct io_uring_rsrc_update {
 	__aligned_u64 data;
 };
 
+/* Skip updating fd indexes set to this value in the fd table */
+#define IORING_REGISTER_FILES_SKIP	(-2)
+
 #define IO_URING_OP_SUPPORTED	(1U << 0)
 
 struct io_uring_probe_op {