Re: [PATCH] fs: io_uring.c: Add skip option for __io_sqe_files_update

[Pavel Begunkov <asml.silence@gmail.com>]

On 20/12/2020 06:50, noah wrote:> From: noah <goldstein.n@wustl.edu>
> 
> This patch makes it so that specify a file descriptor value of -2 will
> skip updating the corresponding fixed file index.
> 
> This will allow for users to reduce the number of syscalls necessary
> to update a sparse file range when using the fixed file option.

Answering the github thread -- it's indeed a simple change, I had it the
same day you posted the issue. See below it's a bit cleaner. However, I
want to first review "io_uring: buffer registration enhancements", and
if it's good, for easier merging/etc I'd rather prefer to let it go
first (even if partially).

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 941fe9b64fd9..b3ae9d5da17e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7847,9 +7847,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 	if (IS_ERR(ref_node))
 		return PTR_ERR(ref_node);
 
-	done = 0;
 	fds = u64_to_user_ptr(up->fds);
-	while (nr_args) {
+	for (done = 0; done < nr_args; done++) {
 		struct fixed_file_table *table;
 		unsigned index;
 
@@ -7858,7 +7857,10 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 			err = -EFAULT;
 			break;
 		}
-		i = array_index_nospec(up->offset, ctx->nr_user_files);
+		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;
 		if (table->files[index]) {
@@ -7896,9 +7898,6 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 				break;
 			}
 		}
-		nr_args--;
-		done++;
-		up->offset++;
 	}
 
 	if (needs_switch) {

-- 
Pavel Begunkov