Re: [PATCH 2/4] block: support compat discard mode by default.

[Dmitry Monakhov <dmonakhov@openvz.org>]

Dmitry Monakhov <dmonakhov@openvz.org> writes:

> Currently there are many filesystems which has implemented
> discard support, but ssd discs not widely used yet.
> Let's allow user to use compat discard mode by default.
> After this feature is enabled by default for all devices which has
> no native discard support it will be possible to use this feature
> simply by passing appropriate mount option to fs (-odiscard in ext4)
BTW i've run tested ext4 with -odiscard option, and it survived more
24hour of stress tests test which consists of fsstress, compilation,
and etc
>
> This default option has many advantages:
> - Hope that this helps in real filesystem testing.
> - People who are crazy about data security whould be really happy.
> - Virtual machine developers also would like this feature.
>
> Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
> ---
>  include/linux/blkdev.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index c762c9f..d7d028c 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1010,7 +1010,7 @@ static inline int sb_issue_discard(struct super_block *sb,
>  	block <<= (sb->s_blocksize_bits - 9);
>  	nr_blocks <<= (sb->s_blocksize_bits - 9);
>  	return blkdev_issue_discard(sb->s_bdev, block, nr_blocks, GFP_KERNEL,
> -				    DISCARD_FL_BARRIER);
> +				    DISCARD_FL_BARRIER|DISCARD_FL_COMPAT);
>  }
>  
>  extern int blk_verify_command(unsigned char *cmd, fmode_t has_write_perm);