On Wed, May 2, 2012 at 4:15 AM, KOSAKI Motohiro
[off-list ref] wrote:

quoted

+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?

Thanks,

Michael

1) P1-T1 uses DIO write (and starting dma)
2) P1-T2 call fork() and makes P2
3) P1-T3 write to the dio target page. and then, cow break occur and
original dio target
   pages is now owned by P2.
4) P2 write the dio target page. It now does NOT make cow break. and
now we break
   dio target page data.
5) DMA transfer write invalid data to disk.

The detail is described in your refer URLs.

quoted

+runs in parallel with a
+.BR fork (2)
+of the reader process, it may happen that the read data is split between
+pages owned by the original process and its child. Thus effectively read
+data is corrupted.
 .LP
 The
 .B O_DIRECT

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/

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