linux-kernel - Re: [PATCH] fat: ignore .. subdir and always add a link to dirs

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Date: Wed, 13 Mar 2024 21:43:36 +0900
From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To: Thadeu Lima de Souza Cascardo <cascardo@...lia.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Gwendal
 Grignou <gwendal@...omium.org>, dlunev@...omium.org
Subject: Re: [PATCH] fat: ignore .. subdir and always add a link to dirs

Thadeu Lima de Souza Cascardo <cascardo@...lia.com> writes:

> On Wed, Mar 13, 2024 at 08:06:41PM +0900, OGAWA Hirofumi wrote:
>> Thadeu Lima de Souza Cascardo <cascardo@...lia.com> writes:
>> 
>> >> So you break the mkdir/rmdir link counting, isn't it?
>> >> 
>> >
>> > It is off by one on those images with directories without ".." subdir.
>> > Otherwise, everything else works fine. mkdir/rmdir inside such directories work
>> > without any issues as rmdir that same directory.
>> 
>> mkdir() increase link count, rmdir decrease link count. Your change set
>> a dir link count always 2? So if there are 3 normal subdirs, and rmdir
>> all those normal dirs, link count underflow.
>> 
>> Thanks.
>> 
>
> No. The main change is as follows:
>
> int fat_subdirs(struct inode *dir)
> {
> [...]
> 	int count = 0;
> [...]
> -		if (de->attr & ATTR_DIR)
> +		if (de->attr & ATTR_DIR &&
> +		    strncmp(de->name, MSDOS_DOTDOT, MSDOS_NAME))
>  			count++;
> [...]
> 	return count;
> }
>
> int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de)
> {
> [...]
> 	if ((de->attr & ATTR_DIR) && !IS_FREE(de->name)) {
> [...]
> -		set_nlink(inode, fat_subdirs(inode));
> +		set_nlink(inode, fat_subdirs(inode) + 1);
> [...]
> }
>
> That is, when first instatiating a directory inode, its link count was set to
> the number of subdirs it had, including "." and "..". Now it is set to 1 + the
> number of subdirs it has ignoring "..".
>
> mkdir and rmdir still increment and decrement the parent directory link count.

Ah, sorry, I misread.  So next, it should create "." and ".." on initial
create/mkdir or such, like mkdir does.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>