[Bug 15568] O_NONBLOCK is NOOP on block devices

[Bug 15568] O_NONBLOCK is NOOP on block devices

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=15568


Petr Baudis <pasky-+ZI9xUNit7I@public.gmane.org> changed:

           What    |Removed                     |Added
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                 CC|                            |pasky-+ZI9xUNit7I@public.gmane.org




--- Comment #1 from Petr Baudis <pasky-+ZI9xUNit7I@public.gmane.org>  2010-05-11 02:09:35 ---
 I find the patch rather intrusive; it seems reasonable to me to devote no more
than a short sentence in the NOTES section to it in each manpage (or more, but
really just in the NOTES section); it should be also noted as of which kernel
version does this hold.

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[Bug 15568] O_NONBLOCK is NOOP on block devices

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=15568





--- Comment #2 from Mike Hayward <mh-linux-kernel-AB0c8HnZplU@public.gmane.org>  2010-05-11 03:38:38 ---
Petr, nice to see you reviewed my patch.  As noted above I have demonstrated
this problem exists on numerous kernel versions both old and new; I have been
using linux extensively for about fifteen years now and there is no reason to
believe that there exists any version in which the semantics are actually
nonblocking.  I do not see that the architecture is or has ever been capable of
nonblocking behavior as this family of calls is tightly coupled to the
submitting thread.  To list all versions of linux and continue to update them
would be awkward at best.  If you can find a version in which it is
nonblocking, I would be interested in testing it and reviewing the code.

It has been so long since I submitting this patch that I have no memory of what
exact language is in it, but it was reviewed by a number of other engineers who
did not comment as you have (actually a couple of them wanted more detail). 
Perhaps your idea is a good one and there is a better way; please feel free to
revise or submit another patch if you can improve upon this one.  I think the
important thing is that the actual semantics get documented in the man pages. 
The current incorrect documentation of the behavior of O_NONBLOCK has and
continues to repeatedly lead to confusion, wasted timed and effort, and
unnecessary traffic on lkml as developers eventually learn the actual behavior
and move to libaio, sg, or other nonblocking system calls.

Out of curiousity, do you or anyone else happen to know who the original author
was who documented these io calls as having nonblocking behavior?  It would be
interesting to have the original author's input.

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[Bug 15568] O_NONBLOCK is NOOP on block devices

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=15568





--- Comment #3 from Petr Baudis <pasky-+ZI9xUNit7I@public.gmane.org>  2010-05-11 08:43:41 ---
Mike, I have not meant covering for some possible old versions, but covering
for future versions; if you know which version the man-page documents, you can
decide if you need to check further to see if your version has something new
there.

I don't know who was the original author describing O_NONBLOCK. I have never
really tended to misinterpret this myself, "Many  file  systems and disks were
considered to be fast enough that the implementation of O_NONBLOCK was deemed
unnecessary.  So, O_NONBLOCK may not be available on files and/or disks" seemed
always rather clear to me, but I agree more detail and mentioning this at other
places than read(2) documentation as well would do good.

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[Bug 15568] O_NONBLOCK is NOOP on block devices

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=15568


Samuel Bronson <naesten-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

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                 CC|                            |naesten-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org




--- Comment #4 from Samuel Bronson <naesten-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>  2010-05-12 22:22:37 ---
So, basically, the note should say "as of Linux 2.6.xx, this has never worked
for block devices or files"?

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[Bug 15568] O_NONBLOCK is NOOP on block devices

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=15568


Alan <alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org> changed:

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
                 CC|                            |alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org
         Resolution|                            |OBSOLETE




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