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


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