vsprintf: Change struct printf_spec.precision from s8 to s16

Commit ef0658f3de484bf9b173639cd47544584e01efa5 changed precision
from int to s8.

There is existing kernel code that uses a larger precision.

An example from the audit code:
	vsnprintf(...,..., " msg='%.1024s'", (char *)data);
which overflows precision and truncates to nothing.

Extending precision size fixes the audit system issue.

Other changes:

Change the size of the struct printf_spec.type from u16 to u8 so
sizeof(struct printf_spec) stays as small as possible.
Reorder the struct members so sizeof(struct printf_spec) remains 64 bits
without alignment holes.
Document the struct members a bit more.

Original-patch-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/vsprintf.c

@@ -408,12 +408,12 @@ enum format_type {
 };
 
 struct printf_spec {
-	u16	type;
-	s16	field_width;	/* width of output field */
+	u8	type;		/* format_type enum */
 	u8	flags;		/* flags to number() */
-	u8	base;
-	s8	precision;	/* # of digits/chars */
-	u8	qualifier;
+	u8	base;		/* number base, 8, 10 or 16 only */
+	u8	qualifier;	/* number qualifier, one of 'hHlLtzZ' */
+	s16	field_width;	/* width of output field */
+	s16	precision;	/* # of digits/chars */
 };
 
 static char *number(char *buf, char *end, unsigned long long num,