Re: [PATCH] filemap_fdatasync & related changes

[Chris Mason]

Ok, lets just fix filemap_fdatasync.  We can tackle the msync/fsync
interaction with screwed up FS writepages later, since all of the existing
writepage funcs are safe.  The problems I see with filemap_fdatasync when
writepage returns 1:

The page dirty bit is not reset.
the page is never unlocked.

So how about something like this in filemap_fdatasync

ret = writepage(page) ;
if (ret == 1) {
    /* writepage declined to write it out,
    ** leave it on the locked list, but make
    ** sure the dirty bit stays on so the page
    ** doesn't disappear
    */
    SetPageDirty(page) ;
    UnlockPage(page) ;
}

And then, in filemap_fdatawait:

list_del(&page->list) ;
if (PageDirty(page))
    list_add(&page->list, &mapping->dirty_pages) ;
else
    list_add(&page->list, &mapping->clean_pages) ;

-chris