Re: cifs: Strange O_DIRECT behaviour on non-directio mounts

[Kevin Wolf <kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

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Am 27.06.2014 um 13:14 hat Kevin Wolf geschrieben:
> Hi Steve,
> 
> I just discussed a problem with a qemu user on IRC, which boiled down to
> him trying to open an image file on cifs with O_DIRECT, but not using a
> directio mount. I understand that this probably isn't going to work
> anytime soon (if at all), but it resulted in a rather unhelpful failure
> mode.
> 
> What happens is that cifs lets the open() call succeed even with the
> unsupported O_DIRECT on that mount, but then fails any I/O on the file
> descriptor. I believe this was introduced in commit dca69288 (which I
> think is otherwise pretty useful).
> 
> With the old behaviour, qemu detected what's going on and suggested to
> use a non-O_DIRECT mode to the user, but with the new one, it got rather
> unhappy after failing to find a working O_DIRECT alignment and ran into
> an assertion failure...
> 
> Now I'll certainly fix the latter in qemu, but I also think that the
> behaviour of cifs is rather surprising. Any chance that you can make
> open() with O_DIRECT fail again on non-directio mounts?
> 
> Thanks,
> Kevin

No interest at all, not even to tell me that I'm completely wrong? :-/

Kevin

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