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SubjectRe: O_NONBLOCK is NOOP on block devices
Hi Jeff,

> I guess I should note that I've suggested nonblocking I/O for files
> before:
>
> http://linux.derkeiler.com/Mailing-Lists/Kernel/2004-10/0290.html
>
> I'll also note that enabling such a patch broke apps that accessed cd
> burners, for example, since O_NONBLOCK had some preexisting semantics
> there that I fail to recall.

Sounds like nonblocking read/write calls are strongly tied to threads
instead of state related to a file descriptor. I haven't poked around
in there, but perhaps the current linux io architecture is just too
set in stone to design an efficient non blocking mechanism. It would
be a shame not to fix it simply because some broken apps depend upon
blocking behavior when they have been explicitly specifying O_NONBLOCK
via open or fcntl.

At least for now we can describe it's actual behavior in the man
pages; I will be submitting a man page patch for consideration later
today.

- Mike


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