Re: [PATCH] UBIFS: add tolerance to use variable writesize

[Dirk Behme <dirk.behme@gmail.com>]

Am 15.05.2013 17:41, schrieb Dirk Behme:
> From: Achim Dahlhoff <Achim.Dahlhoff@de.bosch.com>
>
> UBIfs adapts it‘s structures according to the minimum writeSize reported
> by the MTD device. For NOR flash devices, this is normally 1. For NOR
> devices with internal hardware-ECC it might be more, such as the S-Die
> flash chips of Micron which can use an internal ECC if the chip is
> accessed in 32 byte chunks.
>
> The UBIfs mount process checks and compares the writeSize set in the
> image and the writeSize reported from the /dev/mtd . UBIfs will fail
> to mount if the values differ. It should, though, not be a problem to
> mount an image which was created with a writeSize larger than that of
> the MTD, if it is larger by an integer factor.
>
> This commit changes the check in a way so it will allow the image
> writeSize to be larger than that of the MTD by an integer factor.
> It will allow to create images and deploy them on different devices
> using different writeSizes. writeSize found using values of 1, 8 and 32.
>
> Signed-off-by: Achim Dahlhoff <Achim.Dahlhoff@de.bosch.com>
> ---
>   fs/ubifs/sb.c |   12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ubifs/sb.c b/fs/ubifs/sb.c
> index 4c37607..69dd794 100644
> --- a/fs/ubifs/sb.c
> +++ b/fs/ubifs/sb.c
> @@ -351,6 +351,7 @@ static int validate_sb(struct ubifs_info *c, struct ubifs_sb_node *sup)
>   {
>   	long long max_bytes;
>   	int err = 1, min_leb_cnt;
> +	int chk_tmp;
>
>   	if (!c->key_hash) {
>   		err = 2;
> @@ -362,9 +363,16 @@ static int validate_sb(struct ubifs_info *c, struct ubifs_sb_node *sup)
>   		goto failed;
>   	}
>
> -	if (le32_to_cpu(sup->min_io_size) != c->min_io_size) {
> +	/*
> +	 * Allow a min_io_size mismatch in the way that
> +	 * the size in the superblock (the image) is larger by
> +	 * an integer factor. If image-IOsize mod real-IOsize
> +	 * is zero, it should be ok to mount this.
> +	 */
> +	chk_tmp = le32_to_cpu(sup->min_io_size);
> +	if (chk_tmp != c->min_io_size && ((chk_tmp%c->min_io_size) != 0)) {
>   		ubifs_err("min. I/O unit mismatch: %d in superblock, %d real",
> -			  le32_to_cpu(sup->min_io_size), c->min_io_size);
> +			  chk_tmp, c->min_io_size);
>   		goto failed;
>   	}

Any comments on this?

Many thanks

Dirk