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DOC: add printk-formats.txt
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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 <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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rddunlap authored and torvalds committed Nov 13, 2008
1 parent b76f90b commit b67ad18
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2 changes: 2 additions & 0 deletions Documentation/00-INDEX
Original file line number Diff line number Diff line change
Expand Up @@ -290,6 +290,8 @@ powerpc/
- directory with info on using Linux with the PowerPC.
preempt-locking.txt
- info on locking under a preemptive kernel.
printk-formats.txt
- how to get printk format specifiers right
prio_tree.txt
- info on radix-priority-search-tree use for indexing vmas.
ramdisk.txt
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35 changes: 35 additions & 0 deletions Documentation/printk-formats.txt
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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 <[email protected]>

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