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

[noah <goldstein.w.n@gmail.com>]

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.

Signed-off-by: noah <goldstein.w.n@gmail.com>
---
 fs/io_uring.c | 72 ++++++++++++++++++++++++++-------------------------
 1 file changed, 37 insertions(+), 35 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6f9392c35eef..43ab2b7a87d4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7876,42 +7876,44 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 			err = -EFAULT;
 			break;
 		}
-		i = array_index_nospec(up->offset, ctx->nr_user_files);
-		table = &ctx->file_data->table[i >> IORING_FILE_TABLE_SHIFT];
-		index = i & IORING_FILE_TABLE_MASK;
-		if (table->files[index]) {
-			file = table->files[index];
-			err = io_queue_file_removal(data, file);
-			if (err)
-				break;
-			table->files[index] = NULL;
-			needs_switch = true;
-		}
-		if (fd != -1) {
-			file = fget(fd);
-			if (!file) {
-				err = -EBADF;
-				break;
-			}
-			/*
-			 * Don't allow io_uring instances to be registered. If
-			 * UNIX isn't enabled, then this causes a reference
-			 * cycle and this instance can never get freed. If UNIX
-			 * is enabled we'll handle it just fine, but there's
-			 * still no point in allowing a ring fd as it doesn't
-			 * support regular read/write anyway.
-			 */
-			if (file->f_op == &io_uring_fops) {
-				fput(file);
-				err = -EBADF;
-				break;
-			}
-			table->files[index] = file;
-			err = io_sqe_file_register(ctx, file, i);
-			if (err) {
+		if (fd != -2) {
+			i = array_index_nospec(up->offset, ctx->nr_user_files);
+			table = &ctx->file_data->table[i >> IORING_FILE_TABLE_SHIFT];
+			index = i & IORING_FILE_TABLE_MASK;
+			if (table->files[index]) {
+				file = table->files[index];
+				err = io_queue_file_removal(data, file);
+				if (err)
+					break;
 				table->files[index] = NULL;
-				fput(file);
-				break;
+				needs_switch = true;
+			}
+			if (fd != -1) {
+				file = fget(fd);
+				if (!file) {
+					err = -EBADF;
+					break;
+				}
+				/*
+				 * Don't allow io_uring instances to be registered. If
+				 * UNIX isn't enabled, then this causes a reference
+				 * cycle and this instance can never get freed. If UNIX
+				 * is enabled we'll handle it just fine, but there's
+				 * still no point in allowing a ring fd as it doesn't
+				 * support regular read/write anyway.
+				 */
+				if (file->f_op == &io_uring_fops) {
+					fput(file);
+					err = -EBADF;
+					break;
+				}
+				table->files[index] = file;
+				err = io_sqe_file_register(ctx, file, i);
+				if (err) {
+					table->files[index] = NULL;
+					fput(file);
+					break;
+				}
 			}
 		}
 		nr_args--;
-- 
2.29.2