IOPRIO_PRIO_VALUE needs parens around (data) (was: [4.9.1] Compiler warnings in bcache)

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On Tue, 10 Jan 2017, Coly Li wrote:
> On 2017/1/10 上午2:34, Kai Krakow wrote:
> > When compiling kernel 4.9.1, I'm seeing the following warnings:
> > 
> > In file included from ./include/linux/bio.h:23:0,
> >                  from drivers/md/bcache/bcache.h:181,
> >                  from drivers/md/bcache/writeback.c:9:
> > drivers/md/bcache/writeback.c: In Funktion »bch_cached_dev_writeback_init«:
> > ./include/linux/ioprio.h:15:73: Warnung: Klammern um Arithmetik in Operand von »|« empfohlen [-Wparentheses]
> >  #define IOPRIO_PRIO_VALUE(class, data) (((class) << IOPRIO_CLASS_SHIFT) | data)
> >                                                                          ^
> > drivers/md/bcache/writeback.c:515:25: Anmerkung: bei Substitution des Makros »IOPRIO_PRIO_VALUE«
> >   dc->ioprio_bypass    = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_BE_NR-1);
> >                          ^
> > 
> > It suggests to put parentheses around the expression with the "|"
> > operand. No other kernel source files show warnings for me, so maybe it
> > should be fixed.
> > 
> > I would create a patch myself but I'm not sure if it would be correct
> > and sufficient to put parenthesis around "data" like this:
> > 
> > #define IOPRIO_PRIO_VALUE(class, data) (((class) << IOPRIO_CLASS_SHIFT) | (data))

I caught that before submitting to Jens, so its in 4.10.  I agree with 
Coly, however, that (data) should be added but I'm unable to do that at 
the moment.


--
Eric Wheeler



> > 
> 
> Hi Kai Krakow,
> 
> This fix is necessary, please send a patch to IOPRIO_PRIO_VALUE().
> 
> BTW, I don't see dc->ioprio_bypass from upstream kernel source, is it
> from a development tree ?
> 
> 
> -- 
> Coly Li
> --
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