Commit b67ad18b authored by Randy Dunlap's avatar Randy Dunlap Committed by Linus Torvalds

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: default avatarRandy Dunlap <>
Cc: Alexey Dobriyan <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent b76f90b5
......@@ -290,6 +290,8 @@ powerpc/
- directory with info on using Linux with the PowerPC.
- info on locking under a preemptive kernel.
- how to get printk format specifiers right
- info on radix-priority-search-tree use for indexing vmas.
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 <>
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