Re: [PATCH] Fix ext2 error reporting on fsync

[Andrew Morton <akpm@osdl.org>]

Jan Kara <jack@suse.cz> wrote:
>
> > (If you're proposing that we walk the buffer_head list until we somehow
>  > find the list_head or hlist_head which is embedded within the desired
>  > address_space then yes2, but how do we know where to terminate the search?)
>    Yes, that's it. If the list is not circular, then it's easy to find
>  it's head. So what I suggest is to change private_list from a circular
>  list of list_head structures to the non-circular one. And because
>  non-circular list is already implemented in hlist macros I'd simply use
>  those. The only minor hack is that mapping would not contain hlist_head
>  but hlist_node with pprev set to NULL so that we easily recognize it when
>  traversing backwards. Is it clearer now?

Ah, yes.  It could get pretty inefficient in some corner cases, I guess.  A
4GB file will have up to 1000 buffers on that list so we're looking at
potentially O(1000000) operations.

Plan B is to stick with a doubly-linked list, but mark the address_space's
list_head by setting bit 0 of its list_head.next to 1.

The challenge is to implement this in a manner which Linus doesn't notice ;)