On Thu, 2015-12-03 at 12:54 -0800, Joe Perches wrote: > On Thu, 2015-12-03 at 21:51 +0100, Rasmus Villemoes wrote: > > Maurizio Lombardi reported a problem [1] with the %pb extension: It > > doesn't work for sufficiently large bitmaps, since the size is > > stashed > > in the field_width field of the struct printf_spec, which is > > currently > > an s16. Concretely, this manifested itself in > > /sys/bus/pseudo/drivers/scsi_debug/map being empty, since the > > bitmap > > printer got a size of 0, which is the 16 bit truncation of the > > actual > > bitmap size. > > > > We do want to keep struct printf_spec at 8 bytes so that it can > > cheaply be passed by value. The qualifier field is only used for > > internal bookkeeping in format_decode, so we might as well use a > > local > > variable for that. This gives us an additional 8 bits, which we can > > then use for the field width. > > > > To stay in 8 bytes, we need to do a little rearranging and make the > > type member a bitfield as well. For consistency, change all the > > members to bit fields. gcc doesn't generate much worse code with > > these > > changes (in fact, bloat-o-meter says we save 300 bytes - which I > > think > > is a little surprising). > > > > I didn't find a BUILD_BUG/compiletime_assertion/... which would > > work > > outside function context, so for now I just open-coded it. > > > > [1] http://thread.gmane.org/gmane.linux.kernel/2034835 > > Thanks for keeping at this Rasmus. > This seems quite reasonable.
I like most of the stuff here, though, Joe, can we avoid open-coded BUILD_BUG_ON()? -- Andy Shevchenko <andriy.shevche...@linux.intel.com> Intel Finland Oy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
