On Wed, 2018-09-12 at 18:20 +0200, Jan Kara wrote: > On Wed 12-09-18 15:47:12, Kani, Toshi wrote: > > On Wed, 2018-09-12 at 11:24 +0200, Jan Kara wrote: > > > On Tue 11-09-18 09:42:45, Toshi Kani wrote: > > > > Ext4 mount path calls ext4_iget() to obtain the journal inode. This > > > > inode does not support DAX, and 'ext4_da_aops' needs to be set. It > > > > currently works for the DAX mount case because ext4_iget() always set > > > > 'ext4_da_aops' to any regular files. > > > > > > > > ext4_fill_super > > > > ext4_load_journal > > > > ext4_get_journal_inode > > > > ext4_iget > > > > > > > > In preparation to fix ext4_iget() to set 'ext4_dax_aops' for DAX files, > > > > update ext4_should_use_dax() to return false for the journal inode. > > > > > > > > Fixes: 5f0663bb4a64f588f0a2dd6d1be68d40f9af0086 > > > > Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx> > > > > Cc: Jan Kara <jack@xxxxxxx> > > > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > > > > Cc: "Theodore Ts'o" <tytso@xxxxxxx> > > > > Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx> > > > > > > The journal inode is similar to any other 'system' inode we have in ext4. > > > We don't really expect any of the address space operations to be called for > > > it because we don't use page cache with these inodes. Very similar > > > situation is with e.g. quota files. So to me it seems this patch is not > > > really necessary. Or did you observe any bad effects without this patch? > > > > Yes, without this change, mount fails with the error below. I believe > > .bmap operation in ext4_da_aops is necessary for this case. > > > > jbd2_journal_init_inode: Cannot locate journal superblock > > EXT4-fs > > (pmem1): Could not load journal inode > > Ah, OK, forgot about this. Then how about adding: > .bmap = ext4_bmap, > > to ext4_dax_aops? .bmap is completely fine for DAX inodes and there's no > reason to disallow it. Yes, mount -o dax succeeds with the added ext4_bmap in ext4_dax_aops. Thanks! -Toshi
