On 2 May 2012 03:56, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > On Wed, May 2, 2012 at 4:15 AM, KOSAKI Motohiro > <kosaki.motohiro@xxxxxxxxx> wrote: >>> +suffices. However, if the user buffer is not page aligned and direct read >> >> One more thing. direct write also makes data corruption. Think >> following scenario, > > In the light of all of the comments, can someone revise the man-pages > patch that Jan sent? This does not quite describe the entire situation, but something understandable to developers: O_DIRECT IOs should never be run concurrently with fork(2) system call, when the memory buffer is anonymous memory, or comes from mmap(2) with MAP_PRIVATE. Any such IOs, whether submitted with asynchronous IO interface or from another thread in the process, should be quiesced before fork(2) is called. Failure to do so can result in data corruption and undefined behavior in parent and child processes. This restriction does not apply when the memory buffer for the O_DIRECT IOs comes from mmap(2) with MAP_SHARED or from shmat(2). Is that on the right track? I feel it might be necessary to describe this allowance for MAP_SHARED, because some databases may be doing such things, and anyway it gives apps a potential way to make this work if concurrent fork + DIO is very important. -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
