ubifs: correct UBIFS_DFS_DIR_LEN macro definition and improve code clarity

The UBIFS_DFS_DIR_LEN macro, which defines the maximum length of the UBIFS
debugfs directory name, has an incorrect formula and misleading comments.
The current formula is (3 + 1 + 2*2 + 1), which assumes that both UBI device
number and volume ID are limited to 2 characters. However, UBI device number
ranges from 0 to 31 (2 characters), and volume ID ranges from 0 to 127 (up
to 3 characters).

Although the current code works due to the cancellation of mathematical
errors (9 + 1 = 10, which matches the correct UBIFS_DFS_DIR_LEN value), it
can lead to confusion and potential issues in the future.

This patch aims to improve the code clarity and maintainability by making
the following changes:

1. Corrects the UBIFS_DFS_DIR_LEN macro definition to (3 + 1 + 2 + 3 + 1),
   accommodating the maximum lengths of both UBI device number and volume ID,
   plus the separators and null terminator.
2. Updates the snprintf calls to use UBIFS_DFS_DIR_LEN instead of
   UBIFS_DFS_DIR_LEN + 1, removing the unnecessary +1.
3. Modifies the error checks to compare against UBIFS_DFS_DIR_LEN using >=
   instead of >, aligning with the corrected macro definition.
4. Removes the redundant +1 in the dfs_dir_name array definitions in ubi.h
   and debug.h.

While these changes do not affect the runtime behavior, they make the code
more readable, maintainable, and less prone to future errors.

v2->v3:

 - Removes the duplicated UBIFS_DFS_DIR_LEN and UBIFS_DFS_DIR_NAME macro
   definitions in ubifs.h, as they are already defined in debug.h.

Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/ubifs/sysfs.c b/fs/ubifs/sysfs.c
index 1c958148bb87..aae32222f11b 100644
--- a/fs/ubifs/sysfs.c
+++ b/fs/ubifs/sysfs.c
@@ -91,17 +91,17 @@ static struct kset ubifs_kset = {
 int ubifs_sysfs_register(struct ubifs_info *c)
 {
 	int ret, n;
-	char dfs_dir_name[UBIFS_DFS_DIR_LEN+1];
+	char dfs_dir_name[UBIFS_DFS_DIR_LEN];
 
 	c->stats = kzalloc(sizeof(struct ubifs_stats_info), GFP_KERNEL);
 	if (!c->stats) {
 		ret = -ENOMEM;
 		goto out_last;
 	}
-	n = snprintf(dfs_dir_name, UBIFS_DFS_DIR_LEN + 1, UBIFS_DFS_DIR_NAME,
+	n = snprintf(dfs_dir_name, UBIFS_DFS_DIR_LEN, UBIFS_DFS_DIR_NAME,
 		     c->vi.ubi_num, c->vi.vol_id);
 
-	if (n > UBIFS_DFS_DIR_LEN) {
+	if (n >= UBIFS_DFS_DIR_LEN) {
 		/* The array size is too small */
 		ret = -EINVAL;
 		goto out_free;