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Date: Thu, 12 May 2011 14:36:29 -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 Thu, 2011-05-12 at 14:31 -0700, Mingming Cao 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);
> > + }
> > +
>
> Hmm, I could not see the zeroout extent gets marked as initialized here.
> Nothing wrong to expose the wrong data,
Oh, I mean, this is not causing any exposure of wrong data out,
Mingming
> 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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