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Message-ID: <BANLkTi=1vtGBea0aLZXxy9+oKtZ7Og_NUQ@mail.gmail.com>
Date: Fri, 13 May 2011 10:25:25 +0800
From: Yongqiang Yang <xiaoqiangnk@...il.com>
To: Mingming Cao <cmm@...ibm.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 Fri, May 13, 2011 at 5:31 AM, Mingming Cao <cmm@...ibm.com> wrote:
> 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);
>> + }
>> +
Thank you for looking into the patch.
First, I think I need to explain split_flag added in the patch. There
are three flags in split_flag1.
1.EXT4_EXT_MAY_ZEROOUT means whole extent can be zeroouted instead of
splitting when splitting fails due to ENOSPACE;
2.EXT4_EXT_MARK_UNINIT1 indicates that the 1st part extent should be
marked uninitialized, otherwise initialized.
3.EXT4_EXT_MARK_UNINIT2 is similar to EXT4_EXT_MARK_UNINIT1, only
difference is that it has effect on the 2nd extent.
>
> 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?
Here the extent [ee_block, ee_block + ee_len) is split into two
extents [ee_block, map->m_lblk + map->m_len) and [map->m_lblk +
map->m_len, ee_block + ee_len), which are marked same as ex.
>
> 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?
Yes, error handling is missed.
>
>
>> + 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;
Up to now, zeroout part will be marked initialized.
>> + 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
>
>
>
--
Best Wishes
Yongqiang Yang
--
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