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Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits

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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.

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[PATCH v3 00/14] printf stuff for 4.5 Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
  [PATCH v3 01/14] lib/vsprintf.c: pull out padding code from dentry_name() Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
  Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Joe Perches <joe@perches.com> - 2015-12-03 22:00 +0100
    Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2015-12-03 22:40 +0100
      Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Andrew Morton <akpm@linux-foundation.org> - 2015-12-04 00:40 +0100
        Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Joe Perches <joe@perches.com> - 2015-12-04 01:10 +0100
          Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-04 10:10 +0100
        Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-04 10:10 +0100
      Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Joe Perches <joe@perches.com> - 2015-12-04 00:50 +0100
  [PATCH v3 08/14] lib/test_printf.c: don't BUG Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
  [PATCH v3 03/14] lib/vsprintf.c: eliminate potential race in string() Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
  [PATCH v3 06/14] lib/vsprintf.c: warn about too large precisions and field widths Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
  [PATCH v3 09/14] lib/test_printf.c: check for out-of-bound writes Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
  [PATCH v3 02/14] lib/vsprintf.c: move string() below widen_string() Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
  [PATCH v3 14/14] lib/test_printf.c: test dentry printing Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100
    Re: [PATCH v3 14/14] lib/test_printf.c: test dentry printing Andrew Morton <akpm@linux-foundation.org> - 2015-12-04 01:20 +0100
      Re: [PATCH v3 14/14] lib/test_printf.c: test dentry printing Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-04 09:20 +0100
        Re: [PATCH v3 14/14] lib/test_printf.c: test dentry printing Andrew Morton <akpm@linux-foundation.org> - 2015-12-04 09:50 +0100
  [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-03 22:00 +0100

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