linux-ext4 - Re: [PATCH 3/3] Add batched discard support for ext4

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Message-ID: <20100807222540.GA3573@quack.suse.cz>
Date:	Sun, 8 Aug 2010 00:25:40 +0200
From:	Jan Kara <jack@...e.cz>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, dmonakhov@...nvz.org,
	jmoyer@...hat.com, rwheeler@...hat.com, eshishki@...hat.com,
	sandeen@...hat.com, jack@...e.cz, tytso@....edu
Subject: Re: [PATCH 3/3] Add batched discard support for ext4

On Fri 06-08-10 13:31:16, Lukas Czerner wrote:
...
> +/**
> + * ext4_trim_fs() -- trim ioctl handle function
> + * @sb:			superblock for filesystem
> + * @start:		First Byte to trim
> + * @len:		number of Bytes to trim from start
> + * @minlen:		minimum extent length in Bytes
> + *
> + * ext4_trim_fs goes through all allocation groups containing Bytes from
> + * start to start+len. For each such a group ext4_trim_all_free function
> + * is invoked to trim all free space.
> + */
> +int ext4_trim_fs(struct super_block *sb, uint64_t start, uint64_t len,
> +		uint64_t minlen)
> +{
> +	struct ext4_buddy e4b;
> +	ext4_fsblk_t first_group, last_group;
> +	ext4_group_t group, ngroups = ext4_get_groups_count(sb);
> +	ext4_grpblk_t cnt, first_block, last_block;
> +	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
> +	int ret = 0;
> +
> +	start >>= sb->s_blocksize_bits;
> +	len >>= sb->s_blocksize_bits;
> +	minlen >>= sb->s_blocksize_bits;
> +
> +	if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
> +		return -EINVAL;
> +
> +	/* Determine first and last group to examine based on start and len */
> +	first_group = (start - le32_to_cpu(es->s_first_data_block)) /
> +		      EXT4_BLOCKS_PER_GROUP(sb);
> +	last_group = (start + len - le32_to_cpu(es->s_first_data_block)) /
> +		     EXT4_BLOCKS_PER_GROUP(sb);
> +	last_group = (last_group > ngroups - 1) ? ngroups - 1 : last_group;
> +
> +	if (first_group > last_group)
> +		return -EINVAL;
> +
> +	first_block = start % EXT4_BLOCKS_PER_GROUP(sb);
  I think you should substract "le32_to_cpu(es->s_first_data_block)" from
the start before doing modulo.

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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