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    SubjectRe: [PATCH 0/3] Fix IO error reporting on fsync()
    > On Fri, 6 Oct 2006 13:49:47 +0200
    > Jan Kara <> 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.
    I agree (at least with the second part ;). I can write a patch which
    keeps the inode size but the code will be uglier... Another possibility
    is to put there just a buffer_head pointer and allocate buffer head
    dynamically. That has an advantage that only filesystems using metadata_list
    has to bear the memory cost...

    > What about putting an address_space* into the buffer_head? Transfer the
    > EIO state into the address_space within, say, __remove_assoc_queue()?
    Yes, that's of course possible. But it enlarges each buffer head by 4
    bytes (or 8 on 64-bit arch). Hmm, but you are right that on the systems
    I've looked at this would actually be less memory. OK, I'll write this
    version of the patch.
    Jan Kara <>
    SuSE CR Labs
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      Last update: 2006-10-09 13:43    [W:0.020 / U:0.996 seconds]
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