> > in <linux/list.h> (as opposed to the braindamaged BSD compatibility macros
> > in <linux/lists.h>), and it's fairly trivial to just keep each dirty block
> > on two dirty lists (one inode-specific, one global - you'd still use the
> > global one for normal write-outs).
> >
> > This works for ext2, but it doesn't work with filesystems (most notably
> > FAT filesystems, and possibly some B-tree based filesystems) where
> > metadata might be shared by multiple files, so a block might have to be
> > on multiple inode dirty lists. I had thought about using a linked list
> > architecture and threading buffer_head structures onto inode dirty
> > linked lists, but I discarded that plan since it wouldn't work for all
> > filesystems.
>
> As a percentage the number of 'shared blocks' is low. So just keep a single
> 'might be shared list' and write that list out too.
That really starts to resemble *BSD buffer cache architecture - they just
index buffer cache by inode + offset instead of device + offset, assign
negative offsets to metadata (on normal filesystems) and for FAT they keep
metadata assigned to the device itself.
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