Re: [PATCH] Fix ext2 error reporting on fsync

[Andrew Morton <akpm@osdl.org>]

Jan Kara <jack@suse.cz> wrote:
>
> > It's not much complexity: a few set_bits and test_and_clear_bits in three
>  > places.  The main drawback is a larger buffer_head.
>  > 
>  > Yeah, it's a pita, but it is a data-integrity correctness thing.
>    There's a way to avoid the extra pointer in buffer_head: we could
>  change the circular linked list b_assoc_buffers to a non-circular one
>  (probably use hlists). Then if we find a buffer with IO error, we could
>  find a list head and from it compute the pointer to the mapping... It
>  would not be fast but on IO error I think we could afford it. Do you think
>  it's a good idea?

I don't understand.  We have a pointer to a buffer_head against the
blockdev mapping and we want to find, from that, the S_ISREG address_space
which has connected that buffer to itself.  Precisely how are you proposing
that we do that?

(If you're saying that the hlist space saving would allow us to add an
address_space* pointer to the bh at no space cost then yes).

(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?)