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Subject[PATCH v8 05/18] 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 | 42 +++++++++++++++++++++++++++++++-----------
1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c94780075b04..249a97b19181 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;
@@ -3857,10 +3872,6 @@ static ssize_t ext4_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
if (ext4_has_inline_data(inode))
return 0;

- /* DAX uses iomap path now */
- if (WARN_ON_ONCE(IS_DAX(inode)))
- return 0;
-
trace_ext4_direct_IO_enter(inode, offset, count, iov_iter_rw(iter));
if (iov_iter_rw(iter) == READ)
ret = ext4_direct_IO_read(iocb, iter);
@@ -3946,6 +3957,13 @@ 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 = {
+ .writepages = ext4_dax_writepages,
+ .direct_IO = noop_direct_IO,
+ .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 +3976,9 @@ 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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