linux-kernel - Re: [RFC][PATCH] printk: Add %pb to print bitmaps

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Message-ID: <1336571947.2527.47.camel@twins>
Date:	Wed, 09 May 2012 15:59:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Igor Mammedov <imammedo@...hat.com>, Jiang Liu <liuj97@...il.com>,
	linux-kernel@...r.kernel.org, pjt@...gle.com, tglx@...utronix.de,
	seto.hidetoshi@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH] printk: Add %pb to print bitmaps

On Wed, 2012-05-09 at 15:44 +0200, Peter Zijlstra wrote:
> On Wed, 2012-05-09 at 15:36 +0200, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > @@ -857,15 +860,19 @@ int kptr_restrict __read_mostly;
> > >   *       correctness of the format string and va_list arguments.
> > >   * - 'K' For a kernel pointer that should be hidden from unprivileged users
> > >   * - 'NF' For a netdev_features_t
> > > + * - 'b' For a bitmap, consumes 2 args, second is int
> > 
> > hm, won't the second arg confuse gcc's printf format checker?
> 
> 
> Ah, yes, I suppose I could abuse something like %*pb. Let me try that.

I guess I should use %.*pb and keep the field_width in case someone
manages to actually make bitmap_scnlistprintf() conform to it. The
precision is unused anyway.

The current implementation limits both (field_width and precision) to
s16, which will limit us to printing 32Kb bitmaps. If need arises we
could increase printf_spec size I guess.

---
 lib/vsprintf.c |   29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index abbabec..6eb30a9 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -25,6 +25,9 @@
 #include <linux/kallsyms.h>
 #include <linux/uaccess.h>
 #include <linux/ioport.h>
+#include <linux/bitmap.h>
+#include <linux/cpumask.h>
+#include <linux/numa.h>
 #include <net/addrconf.h>
 
 #include <asm/page.h>		/* for PAGE_SIZE */
@@ -857,6 +860,9 @@ int kptr_restrict __read_mostly;
  *       correctness of the format string and va_list arguments.
  * - 'K' For a kernel pointer that should be hidden from unprivileged users
  * - 'NF' For a netdev_features_t
+ * - 'b' For a bitmap; %.*pb is required and the precision is used as bitmap length
+ * - 'bc' For a cpumask
+ * - 'bn' For a nodemask
  *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a
@@ -941,6 +947,26 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 			return netdev_feature_string(buf, end, ptr, spec);
 		}
 		break;
+	case 'b':
+		{
+			int bits, len;
+
+			switch (fmt[1]) {
+			case 'c':
+				bits = nr_cpumask_bits;
+				break;
+			case 'n':
+				bits = MAX_NUMNODES;
+				break;
+			default:
+				bits = spec->precision;
+				break;
+			}
+		       
+			len = bitmap_scnlistprintf(buf, end - buf, ptr, bits);
+
+			return buf + len;
+		}
 	}
 	spec.flags |= SMALL;
 	if (spec.field_width == -1) {
@@ -1175,6 +1201,9 @@ int format_decode(const char *fmt, struct printf_spec *spec)
  * %pI6c print an IPv6 address as specified by RFC 5952
  * %pU[bBlL] print a UUID/GUID in big or little endian using lower or upper
  *   case.
+ * %.*pb print a bitmap list using the precision as bitmap length
+ * %pbc print a cpumask bitmap
+ * %pbn print a nodemask bitmap
  * %n is ignored
  *
  * The return value is the number of characters which would

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