linux-kernel - Re: [PATCH] UBIFS: compute KSA size and store in superblock

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Date:	Fri, 25 May 2012 16:24:31 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Joel Reardon <joel@...mbassador.com>
Cc:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] UBIFS: compute KSA size and store in superblock

On Fri, 2012-05-25 at 15:10 +0200, Joel Reardon wrote:
> This patch makes the super block reserve space for the KSA. It computes the
> number of KSA LEBs and adds the ksa_lebs to on-medium superblock. The value is
> read off the media. The decision to use a KSA is controlled by use_ubifsec
> switch, also added to the superblock, ubifs_info, and is controlled as a mount
> option.
> 
> This is tested by creating a drive and checking the mount debug output. The
> number of LEBS assigned during create_default_filesystem was changed to ensure
> that remounting does infact read the old value. When the use_ubifsec option
> was not enabled, no LEBs were assigned. Integck was run and the drive was
> filled to capacity. The LEBs in the KSA were not used when filled.
> 
> Signed-off-by: Joel Reardon <reardonj@....ethz.ch>

I do not have to time to review it now, but please, make sure that the
KSA size is according to 'max_leb_cnt' (see the --max-leb-cnt of the
mkfs.ubifs tool). Also, think about this use-case in general: you have
UBI volume of size X, then the volume is resized to Y > X, then mounted
- UBIFS should work and resize itself to Y, up to the 'max_leb_cnt'. If
Y > 'max_leb_cnt', we resize only to 'max_leb_cnt'.

>  struct ubifs_sb_node {
>  	struct ubifs_ch ch;
> @@ -649,7 +651,9 @@ struct ubifs_sb_node {
>  	__le32 time_gran;
>  	__u8 uuid[16];
>  	__le32 ro_compat_version;
> -	__u8 padding2[3968];
> +	__le32 ksa_lebs;
> +	__u8 use_ubifsec;

If it is only one bit, document that only one bit (LSB?) is used. In the
future someone can add more bits there, and rename it, theoretically
(unlikely though).

-- 
Best Regards,
Artem Bityutskiy

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