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

Peter Zijlstra
2012-05-09T13:59:18Z

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@infradead.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