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    Subject[PATCH v7 05/14] ext4, dax: introduce ext4_dax_aops
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    In preparation for the dax implementation to start associating dax pages
    to inodes via page->mapping, we need to provide a 'struct
    address_space_operations' instance for dax. Otherwise, direct-I/O
    triggers incorrect page cache assumptions and warnings.

    Cc: "Theodore Ts'o" <tytso@mit.edu>
    Cc: Andreas Dilger <adilger.kernel@dilger.ca>
    Cc: linux-ext4@vger.kernel.org
    Cc: Jan Kara <jack@suse.cz>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    ---
    fs/ext4/inode.c | 38 +++++++++++++++++++++++++++++++-------
    1 file changed, 31 insertions(+), 7 deletions(-)

    diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
    index c94780075b04..f9884e41cb39 100644
    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -2725,12 +2725,6 @@ static int ext4_writepages(struct address_space *mapping,
    percpu_down_read(&sbi->s_journal_flag_rwsem);
    trace_ext4_writepages(inode, wbc);

    - if (dax_mapping(mapping)) {
    - ret = dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev,
    - wbc);
    - goto out_writepages;
    - }
    -
    /*
    * No pages to write? This is mainly a kludge to avoid starting
    * a transaction for special inodes like journal inode on last iput()
    @@ -2955,6 +2949,27 @@ static int ext4_writepages(struct address_space *mapping,
    return ret;
    }

    +static int ext4_dax_writepages(struct address_space *mapping,
    + struct writeback_control *wbc)
    +{
    + int ret;
    + long nr_to_write = wbc->nr_to_write;
    + struct inode *inode = mapping->host;
    + struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
    +
    + if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
    + return -EIO;
    +
    + percpu_down_read(&sbi->s_journal_flag_rwsem);
    + trace_ext4_writepages(inode, wbc);
    +
    + ret = dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev, wbc);
    + trace_ext4_writepages_result(inode, wbc, ret,
    + nr_to_write - wbc->nr_to_write);
    + percpu_up_read(&sbi->s_journal_flag_rwsem);
    + return ret;
    +}
    +
    static int ext4_nonda_switch(struct super_block *sb)
    {
    s64 free_clusters, dirty_clusters;
    @@ -3946,6 +3961,13 @@ static const struct address_space_operations ext4_da_aops = {
    .error_remove_page = generic_error_remove_page,
    };

    +static const struct address_space_operations ext4_dax_aops = {
    + .direct_IO = ext4_direct_IO,
    + .writepages = ext4_dax_writepages,
    + .set_page_dirty = noop_set_page_dirty,
    + .invalidatepage = noop_invalidatepage,
    +};
    +
    void ext4_set_aops(struct inode *inode)
    {
    switch (ext4_inode_journal_mode(inode)) {
    @@ -3958,7 +3980,9 @@ void ext4_set_aops(struct inode *inode)
    default:
    BUG();
    }
    - if (test_opt(inode->i_sb, DELALLOC))
    + if (IS_DAX(inode))
    + inode->i_mapping->a_ops = &ext4_dax_aops;
    + else if (test_opt(inode->i_sb, DELALLOC))
    inode->i_mapping->a_ops = &ext4_da_aops;
    else
    inode->i_mapping->a_ops = &ext4_aops;
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