linux-kernel - Re: [RFC PATCH] vfat:avoid unnecessary check

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Message-ID: <tencent_F5322517AD2A723568849905CF474A7D6C07@qq.com>
Date: Fri,  5 Sep 2025 23:49:05 +0800
From: zhoumin <teczm@...mail.com>
To: hirofumi@...l.parknet.co.jp
Cc: linux-kernel@...r.kernel.org,
	teczm@...mail.com
Subject: Re: [RFC PATCH] vfat:avoid unnecessary check

Hi Hirofumi

>> Remove redundant and unreachable name check code in dir.c.

> Looks like you changed the logic, but no explanation.

1. In fat_parse_long:
If (*de)->name[0] equals DELETED_FLAG, the function returns immediately.
Consequently, the subsequent IS_FREE check can never evaluate to true.
Therefore, retaining only the ATTR_VOLUME verification should be sufficient.

2. In fat_search_long:
If (*de)->name[0] equals DELETED_FLAG, the loop skips to the next iteration.
This makes the subsequent checks for IS_FREE and ATTR_EXT unreachable.These
checks should therefore be removed.

3. In __fat_readdir:
The same reasoning as in fat_search_long applies here.

>> Remove flags check in fat_update_time since fat does not support
>> inode version.
>>
>> Optimize fat_truncate_time to return a meaningful value, allowing
>> the removal of redundant inode checks in fat_update_time. This
>> ensures non-root inodes are validated only once.

> Also changed the logic, you removed the check of flags.

Changing the return value of fat_truncate_time and removing the ino check in 
fat_update_time is a minor optimization, as mentioned in my previous patch email.

The reason for removing the flags check is that the enum file_time_flags has
only four values. Since vfat does not support SB_I_VERSION, higher-level
functions such as inode_needs_update_time or inode_update_timestamps will never
set flags with S_VERSION. Thus, checking the flags is unnecessary.

Note that __mark_inode_dirty will not be called only for the root inode. This
logic remains consistent with the previous version.

Thanks,

zhoumin