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    Subjectwritepage in inode_operations - never used?

    I was expecting that the writepage member of inode_operations was used
    to write out pages to disk, presumably after they had been written by
    readpage. However, examination of existing code in 2.1.26 (find
    /usr/src/linux -name *.[ch] -exec grep writepage "{}" \; -print)
    reveals that no filesystem code implements it (it is always set to
    NULL) and furthermore, that nothing in the kernel ever calls it. I
    looked in fs/buffer.c and mm/filemap.c where I expected stuff would
    get flushed to disk, and it seems this always happens with ll_rw_block
    to flush buffers directly to the block device they come from, without
    checking for or ever using writepage. Is this functionality that was
    planned but never implemented? I have one additional question. My goal
    in investigating this is that I would like to write a filesystem that
    wants to do something other than the default when buffers it read get
    flushed to disk. NFS clearly manages to achieve this somehow, despite
    the lack of writepage, but how this happens was not clear to me from
    the NFS and buffer cache/page cache code.

    - Maciej Stachowiak

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      Last update: 2005-03-22 13:39    [W:0.015 / U:7.912 seconds]
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