From: Joe Perches on
Add the ability to print a format and va_list from a structure pointer

Allows __dev_printk to be implemented as a single printk while
minimizing string space duplication.

%pV should not be used without some mechanism to verify the
format and argument use ala __attribute__(format (printf(...))).

Signed-off-by: Joe Perches <joe(a)perches.com>
---
include/linux/kernel.h | 5 +++++
lib/vsprintf.c | 9 +++++++++
2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 7f07074..0eae8e9 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -169,6 +169,11 @@ static inline void might_fault(void)
}
#endif

+struct va_format {
+ const char *fmt;
+ va_list *va;
+};
+
extern struct atomic_notifier_head panic_notifier_list;
extern long (*panic_blink)(long time);
NORET_TYPE void panic(const char * fmt, ...)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index af4aaa6..0fd7f8b 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -950,6 +950,11 @@ static char *uuid_string(char *buf, char *end, const u8 *addr,
* [0][1][2][3]-[4][5]-[6][7]-[8][9]-[10][11][12][13][14][15]
* little endian output byte order is:
* [3][2][1][0]-[5][4]-[7][6]-[8][9]-[10][11][12][13][14][15]
+ * - 'V' For a struct va_format which contains a format string * and va_list *,
+ * call vsnprintf(->format, *->va_list).
+ * Implements a "recursive vsnprintf".
+ * Do not use this feature without some mechanism to verify the
+ * correctness of the format string and va_list arguments.
*
* Note: The difference between 'S' and 'F' is that on ia64 and ppc64
* function pointers are really function descriptors, which contain a
@@ -994,6 +999,10 @@ static char *pointer(const char *fmt, char *buf, char *end, void *ptr,
break;
case 'U':
return uuid_string(buf, end, ptr, spec, fmt);
+ case 'V':
+ return buf + vsnprintf(buf, end - buf,
+ ((struct va_format *)ptr)->fmt,
+ *(((struct va_format *)ptr)->va));
}
spec.flags |= SMALL;
if (spec.field_width == -1) {
--
1.7.0.14.g7e948

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