path: root/Documentation/printk-formats.txt
diff options
authorRandy Dunlap <>2008-11-12 13:26:55 -0800
committerLinus Torvalds <>2008-11-12 17:17:17 -0800
commitb67ad18b06701b77ca8bfe9bb760c5c9e765e3cf (patch)
treef0b87e5fceec394f096e932db1f0a5fb7b104f50 /Documentation/printk-formats.txt
parentb76f90b526737070302a127c710263e2ac707676 (diff)
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 <> Cc: Alexey Dobriyan <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'Documentation/printk-formats.txt')
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diff --git a/Documentation/printk-formats.txt b/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 <>