Messages in this thread | | | Date | Mon, 23 Nov 2015 18:19:35 -0500 | From | Tejun Heo <> | Subject | Re: [PATCH 04/14] lib/vsprintf.c: expand field_width to 24 bits |
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On Mon, Nov 23, 2015 at 10:29:21PM +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 > > Reported-by: Maurizio Lombardi <mlombard@redhat.com> > Cc: Tejun Heo <tj@kernel.org> > Cc: Joe Perches <joe@perches.com> > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
FWIW,
Acked-by: Tejun Heo <tj@kernel.org>
Thanks.
-- tejun
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