Re: [PATCH 0/3] Fix IO error reporting on fsync()

[Andrew Morton]

On Fri, 6 Oct 2006 13:49:47 +0200
Jan Kara <jack@xxxxxxx> wrote:

>   current code in buffer.c has two pitfalls that cause problems with IO
> error reporting of filesystems using mapping->private_list for their
> metadata buffers (e.g. ext2).
>   The first problem is that end_io_async_write() does not mark IO error
> in the buffer flags, only in the page flags. Hence fsync_buffers_list()
> does not find out that some IO error has occured and will not report it.
>   The second problem is that buffers from private_list can be freed
> (e.g. under memory pressure) and if fsync_buffer_list() is called after
> that moment, IO error is lost - note that metadata buffers mark AS_EIO
> on the *device mapping* not on the inode mapping.
>   Following series of three patches tries to fix these problems. The
> approach I took (after some discussions with Andrew) is introducing
> dummy buffer_head in the mapping instead of private_list. This dummy
> buffer head serves as a head of metadata buffer list and also collects
> IO errors from other buffers on the list (see the third patch for more
> details). This is kind of compromise between introducing a pointer to
> inode's address_space into each buffer and between using list_head
> instead of buffer_head and playing some dirty tricks to recognize that
> one particular list_head is actually from address_space and not from
> buffer_head. Any suggestions for improvements welcome.

This is really complex, and enlarges the inode by quite a lot, which hurts.

What about putting an address_space* into the buffer_head?  Transfer the
EIO state into the address_space within, say, __remove_assoc_queue()?
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