DOC: add printk-formats.txt

Add printk-formats.txt so that we don't have to keep fixing the
same things over and over again.  <wishful thinking>

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
new file mode 100644
index 000000000000..1b5a5ddbc3ef
--- /dev/null
+++ b/Documentation/printk-formats.txt
@@ -0,0 +1,35 @@
+If variable is of Type,		use printk format specifier:
+---------------------------------------------------------
+		int			%d or %x
+		unsigned int		%u or %x
+		long			%ld or %lx
+		unsigned long		%lu or %lx
+		long long		%lld or %llx
+		unsigned long long	%llu or %llx
+		size_t			%zu or %zx
+		ssize_t			%zd or %zx
+
+Raw pointer value SHOULD be printed with %p.
+
+u64 SHOULD be printed with %llu/%llx, (unsigned long long):
+
+	printk("%llu", (unsigned long long)u64_var);
+
+s64 SHOULD be printed with %lld/%llx, (long long):
+
+	printk("%lld", (long long)s64_var);
+
+If <type> is dependent on a config option for its size (e.g., sector_t,
+blkcnt_t, phys_addr_t, resource_size_t) or is architecture-dependent
+for its size (e.g., tcflag_t), use a format specifier of its largest
+possible type and explicitly cast to it.  Example:
+
+	printk("test: sector number/total blocks: %llu/%llu\n",
+		(unsigned long long)sector, (unsigned long long)blockcount);
+
+Reminder: sizeof() result is of type size_t.
+
+Thank you for your cooperation and attention.
+
+
+By Randy Dunlap <rdunlap@xenotime.net>