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Message-ID: <1305235906.9708.81.camel@mingming-laptop>
Date: Thu, 12 May 2011 14:31:46 -0700
From: Mingming Cao <cmm@...ibm.com>
To: Yongqiang Yang <xiaoqiangnk@...il.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu,
achender@...ux.vnet.ibm.com
Subject: Re: [PATCH v2 2/3] ext4:Add two functions splitting an extent.
On Mon, 2011-05-02 at 19:05 -0700, Yongqiang Yang wrote:
> v0 -> v1:
> -- coding style
> -- try to merge extents in zeroout case too.
>
> 1] Add a function named ext4_split_extent_at() which splits an extent
> into two extents at given logical block.
>
> 2] Add a function called ext4_split_extent() which splits an extent
> into three extents.
>
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
> Tested-by: Allison Henderson <achender@...ux.vnet.ibm.com>
> ---
> fs/ext4/extents.c | 187 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 187 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 11f30d2..db1d67c 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2554,6 +2554,193 @@ static int ext4_ext_zeroout(struct inode *inode, struct ext4_extent *ex)
> return ret;
> }
>
> +/*
> + * used by extent splitting.
> + */
> +#define EXT4_EXT_MAY_ZEROOUT 0x1 /* safe to zeroout if split fails \
> + due to ENOSPC */
> +#define EXT4_EXT_MARK_UNINIT1 0x2 /* mark first half uninitialized */
> +#define EXT4_EXT_MARK_UNINIT2 0x4 /* mark second half uninitialized */
> +
> +/*
> + * ext4_split_extent_at() splits an extent at given block.
> + *
> + * @handle: the journal handle
> + * @inode: the file inode
> + * @path: the path to the extent
> + * @split: the logical block where the extent is splitted.
> + * @split_flags: indicates if the extent could be zeroout if split fails, and
> + * the states(init or uninit) of new extents.
> + * @flags: flags used to insert new extent to extent tree.
> + *
> + *
> + * Splits extent [a, b] into two extents [a, @split) and [@split, b], states
> + * of which are deterimined by split_flag.
> + *
> + * There are two cases:
> + * a> the extent are splitted into two extent.
> + * b> split is not needed, and just mark the extent.
> + *
> + * return 0 on success.
> + */
> +static int ext4_split_extent_at(handle_t *handle,
> + struct inode *inode,
> + struct ext4_ext_path *path,
> + ext4_lblk_t split,
> + int split_flag,
> + int flags)
> +{
> + ext4_fsblk_t newblock;
> + ext4_lblk_t ee_block;
> + struct ext4_extent *ex, newex, orig_ex;
> + struct ext4_extent *ex2 = NULL;
> + unsigned int ee_len, depth;
> + int err = 0;
> +
> + ext_debug("ext4_split_extents_at: inode %lu, logical"
> + "block %llu\n", inode->i_ino, (unsigned long long)split);
> +
> + ext4_ext_show_leaf(inode, path);
> +
> + depth = ext_depth(inode);
> + ex = path[depth].p_ext;
> + ee_block = le32_to_cpu(ex->ee_block);
> + ee_len = ext4_ext_get_actual_len(ex);
> + newblock = split - ee_block + ext4_ext_pblock(ex);
> +
> + BUG_ON(split < ee_block || split >= (ee_block + ee_len));
> +
> + err = ext4_ext_get_access(handle, inode, path + depth);
> + if (err)
> + goto out;
> +
> + if (split == ee_block) {
> + /*
> + * case b: block @split is the block that the extent begins with
> + * then we just change the state of the extent, and splitting
> + * is not needed.
> + */
> + if (split_flag & EXT4_EXT_MARK_UNINIT2)
> + ext4_ext_mark_uninitialized(ex);
> + else
> + ext4_ext_mark_initialized(ex);
> +
> + if (!(flags & EXT4_GET_BLOCKS_PRE_IO))
> + ext4_ext_try_to_merge(inode, path, ex);
> +
> + err = ext4_ext_dirty(handle, inode, path + depth);
> + goto out;
> + }
> +
> + /* case a */
> + memcpy(&orig_ex, ex, sizeof(orig_ex));
> + ex->ee_len = cpu_to_le16(split - ee_block);
> + if (split_flag & EXT4_EXT_MARK_UNINIT1)
> + ext4_ext_mark_uninitialized(ex);
> +
> + /*
> + * path may lead to new leaf, not to original leaf any more
> + * after ext4_ext_insert_extent() returns,
> + */
> + err = ext4_ext_dirty(handle, inode, path + depth);
> + if (err)
> + goto fix_extent_len;
> +
> + ex2 = &newex;
> + ex2->ee_block = cpu_to_le32(split);
> + ex2->ee_len = cpu_to_le16(ee_len - (split - ee_block));
> + ext4_ext_store_pblock(ex2, newblock);
> + if (split_flag & EXT4_EXT_MARK_UNINIT2)
> + ext4_ext_mark_uninitialized(ex2);
> +
> + err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
> + if (err == -ENOSPC && (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
> + err = ext4_ext_zeroout(inode, &orig_ex);
> + if (err)
> + goto fix_extent_len;
> + /* update the extent length and mark as initialized */
> + ex->ee_len = cpu_to_le32(ee_len);
> + ext4_ext_try_to_merge(inode, path, ex);
> + err = ext4_ext_dirty(handle, inode, path + depth);
> + goto out;
> + } else if (err)
> + goto fix_extent_len;
> +
> +out:
> + ext4_ext_show_leaf(inode, path);
> + return err;
> +
> +fix_extent_len:
> + ex->ee_len = orig_ex.ee_len;
> + ext4_ext_dirty(handle, inode, path + depth);
> + return err;
> +}
> +
> +/*
> + * ext4_split_extents() splits an extent and mark extent which is covered
> + * by @map as split_flags indicates
> + *
> + * It may result in splitting the extent into multiple extents (upto three)
> + * There are three possibilities:
> + * a> There is no split required
> + * b> Splits in two extents: Split is happening at either end of the extent
> + * c> Splits in three extents: Somone is splitting in middle of the extent
> + *
> + */
> +static int ext4_split_extent(handle_t *handle,
> + struct inode *inode,
> + struct ext4_ext_path *path,
> + struct ext4_map_blocks *map,
> + int split_flag,
> + int flags)
> +{
> + ext4_lblk_t ee_block;
> + struct ext4_extent *ex;
> + unsigned int ee_len, depth;
> + int err = 0;
> + int uninitialized;
> + int split_flag1, flags1;
> +
> + depth = ext_depth(inode);
> + ex = path[depth].p_ext;
> + ee_block = le32_to_cpu(ex->ee_block);
> + ee_len = ext4_ext_get_actual_len(ex);
> + uninitialized = ext4_ext_is_uninitialized(ex);
> +
> + if (map->m_lblk + map->m_len < ee_block + ee_len) {
> + split_flag1 = split_flag & EXT4_EXT_MAY_ZEROOUT ?
> + EXT4_EXT_MAY_ZEROOUT : 0;
> + flags1 = flags | EXT4_GET_BLOCKS_PRE_IO;
> + if (uninitialized)
> + split_flag1 |= EXT4_EXT_MARK_UNINIT1 |
> + EXT4_EXT_MARK_UNINIT2;
> + err = ext4_split_extent_at(handle, inode, path,
> + map->m_lblk + map->m_len, split_flag1, flags1);
> + }
> +
Hmm, I could not see the zeroout extent gets marked as initialized here.
Nothing wrong to expose the wrong data, but certainly we are not take
advantage of zero out, Perhaps I missed something?
It would be nice to add some comments to describe the difference of
split_flag1, flags1, flags:-) Thanks.
Also, I think we miss error handling here. What if the first split
failed and return error here? we still proceed to to do next split? I
think we should go to the err exit, isnt?
> + ext4_ext_drop_refs(path);
> + path = ext4_ext_find_extent(inode, map->m_lblk, path);
> + if (IS_ERR(path))
> + return PTR_ERR(path);
> +
> + if (map->m_lblk >= ee_block) {
> + split_flag1 = split_flag & EXT4_EXT_MAY_ZEROOUT ?
> + EXT4_EXT_MAY_ZEROOUT : 0;
> + if (uninitialized)
> + split_flag1 |= EXT4_EXT_MARK_UNINIT1;
> + if (split_flag & EXT4_EXT_MARK_UNINIT2)
> + split_flag1 |= EXT4_EXT_MARK_UNINIT2;
> + err = ext4_split_extent_at(handle, inode, path,
> + map->m_lblk, split_flag1, flags);
> + if (err)
> + goto out;
> + }
> +
> + ext4_ext_show_leaf(inode, path);
> +out:
> + return err ? err : map->m_len;
> +}
> +
> #define EXT4_EXT_ZERO_LEN 7
> /*
> * This function is called by ext4_ext_map_blocks() if someone tries to write
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