[Ocfs2-devel] [patch 09/15] ocfs2: add functions to add and remove inode in orphan dir

[Mark Fasheh]

On Mon, Dec 22, 2014 at 09:04:25AM +0800, Joseph Qi wrote:
> >> So after this change, once unlink and dio happen concurrently, there
> >> may be two kinds of results:
> >> 1. On the same node, only one entry will be added with flag
> >> OCFS2_ORPHANED_FL, and flag OCFS2_DIO_ORPHANED_FL will be set and clear
> >> during dio.
> >> 2. On different nodes, two entries will be added with each flag
> >> OCFS2_ORPHANED_FL or OCFS2_DIO_ORPHANED_FL.
> >>
> >> Since entry name is stringified from blkno and the length is fixed
> >> OCFS2_ORPHAN_NAMELEN, so adding a prefix as you suggested may affect
> >> too much.
> > 
> > No, adding the prefix is much more preferable to intentionally corrupting
> > the conents of a directory. That OCFS2_ORPHAN_NAMELEN is a #define does not
> > matter, you are free to make it whatever reasonable value fits the name. The
> > directory code naturally handles this, whtether the length is
> > OCFS2_ORPHAN_NAMELEN or OCFS2_ORPHAN_NAMELEN + PREFIX_NAMELEN.
> > 
> > Also if you were to run fsck against the file system it will (should) complain
> > about having duplciate entries in the orphan dir.
> > 
> > Aside from the corruption issue, there are usability issues too. Someone
> > running "ls //orphan_dir:0000" will not be able to tell whether a name is
> > there for dio or nlink==0. If you prefix it, then debugging becomes much
> > easier.
> > 
> Okay, I will try to take your advice and make a change.

Great, thank you.


> > Btw, did you see my note about a readonly superblock flag for this? We're
> > going to need to handle backward compatibility too.
> Yes. At my first glance, it may need a lot change to support feature ro compat
> at my first glance. I need to investigate on it before do the actual change.
> Thanks.

Kernel should be straight forward - if the flag isn't there just use the
existing fallback. Otherwise we can use the new direct_IO code.

>From memory, in ocfs2-tools you'll have to update mkfs to write the flag,
tunefs to turn it on/off for an existing filesystem and fsck to truncate the
direct-io orphans it finds.
	--Mark

--
Mark Fasheh