LWN: Comments on "Enhanced printk() merged"

Unescaped characters confuse Konqueror

corbet — Wed, 20 Aug 2008 14:46:23 +0000

Not just "better", it's required to make the page valid HTML. Sorry that one slipped through, it's fixed now.

Unescaped characters confuse Konqueror

Robert — Wed, 20 Aug 2008 14:39:10 +0000

The string printk(" [<%016lx>] confuses Konqueror (3.5.9) and it terminates the page behind the <. It would be better to convert these characters to HTML entities: < and >.

Enhanced printk() merged

nix — Thu, 17 Jul 2008 17:41:33 +0000

Yes indeed, and printk() is marked up with the printf attribute. The trick 
is to find a way to define new format characters that doesn't cause GCC to 
warn about all of them.

There were attempts in the past to make the format attributes dynamically 
redefinable, but if I recall correctly the consensus in the end was that 
this was simply too damn complicated.

(I wonder if what we need is loose versions of the format attribute's 
archetypes, which warn about incorrect numbers of parameters and type 
mismatches for format letters GCC knows about, but does not check format 
letters that GCC doesn't know? As long as nobody tries to reimplement 
something like .* which changes the number of arguments consumed, this 
should work fine.)

Enhanced printk() merged

meuh — Thu, 17 Jul 2008 16:41:53 +0000

Extending GCC to support some new kind of format string is also possible,
sadly this can't be done dynamically, patching GCC is required.

GCC already knows about other format string, see:
http://gcc.gnu.org/onlinedocs/gcc-4.3.0/gcc/Target-Format...
http://gcc.gnu.org/onlinedocs/gcc-4.3.0/gcc/Function-Attr...

Enhanced printk() merged

nix — Thu, 17 Jul 2008 09:56:08 +0000

If they used that format, GCC would warn about it. The format chosen looks 
to GCC (as to userland printf()) like a %p with unrelated characters after 
it, so GCC doesn't check those unrelated characters because they're just 
literal text as far as it knows.

Enhanced printk() merged

meuh — Thu, 17 Jul 2008 08:59:32 +0000

Strange way to specify format.

According to printf() manual page:

Each conversion specification is introduced by the '%' character [...] after which the following appear in sequence:

Zero or more flags

[...]

A conversion specifier character that indicates the type of conversion to be applied.

So, the correct way to specify a struct inode pointer should be %Ip, where I is the flag and p the conversion specifier.

Did kernel developers read userland manual pages ? :)