linux-kernel - Re: [PATCH] fs/fat: replace magic numbers with macros from <uapi/linux/msdos

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Message-ID: <87bnkno5he.fsf@mail.parknet.co.jp>
Date:	Sat, 21 Feb 2015 20:42:53 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Alexander Kuleshov <kuleshovmail@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/fat: replace magic numbers with macros from <uapi/linux/msdos_fs.h>

Alexander Kuleshov <kuleshovmail@...il.com> writes:

Those are not EOF, those are mask. For example, EOF_FAT12 can be 0xff8
(some old drivers did this really).

And 0xf0000000 means ~0x0fffffff, not free cluster (because FAT32 is
28bits actually).

> Signed-off-by: Alexander Kuleshov <kuleshovmail@...il.com>
> ---
>  fs/fat/fatent.c               | 8 ++++----
>  include/uapi/linux/msdos_fs.h | 3 +++
>  2 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
> index 260705c..3def7bd 100644
> --- a/fs/fat/fatent.c
> +++ b/fs/fat/fatent.c
> @@ -129,7 +129,7 @@ static int fat12_ent_get(struct fat_entry *fatent)
>  		next = (*ent12_p[1] << 8) | *ent12_p[0];
>  	spin_unlock(&fat12_entry_lock);
>  
> -	next &= 0x0fff;
> +	next &= EOF_FAT12;
>  	if (next >= BAD_FAT12)
>  		next = FAT_ENT_EOF;
>  	return next;
> @@ -146,7 +146,7 @@ static int fat16_ent_get(struct fat_entry *fatent)
>  
>  static int fat32_ent_get(struct fat_entry *fatent)
>  {
> -	int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
> +	int next = le32_to_cpu(*fatent->u.ent32_p) & EOF_FAT32;
>  	WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
>  	if (next >= BAD_FAT32)
>  		next = FAT_ENT_EOF;
> @@ -186,8 +186,8 @@ static void fat16_ent_put(struct fat_entry *fatent, int new)
>  
>  static void fat32_ent_put(struct fat_entry *fatent, int new)
>  {
> -	WARN_ON(new & 0xf0000000);
> -	new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
> +	WARN_ON(new & FAT_FREE_CLUSTER);
> +	new |= le32_to_cpu(*fatent->u.ent32_p) & ~EOF_FAT32;
>  	*fatent->u.ent32_p = cpu_to_le32(new);
>  	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
>  }
> diff --git a/include/uapi/linux/msdos_fs.h b/include/uapi/linux/msdos_fs.h
> index e956704..6d085bf 100644
> --- a/include/uapi/linux/msdos_fs.h
> +++ b/include/uapi/linux/msdos_fs.h
> @@ -58,6 +58,9 @@
>  #define FAT_FIRST_ENT(s, x)	((MSDOS_SB(s)->fat_bits == 32 ? 0x0FFFFF00 : \
>  	MSDOS_SB(s)->fat_bits == 16 ? 0xFF00 : 0xF00) | (x))
>  
> +/* indicates that a cluster is free */
> +#define FAT_FREE_CLUSTER	0xf0000000
> +
>  /* start of data cluster's entry (number of reserved clusters) */
>  #define FAT_START_ENT	2

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