On Fri, 2014-11-07 at 12:01 +0000, Daniel Thompson wrote:
Currently when kdb traps printk messages then the raw log level prefix (consisting of '\001' followed by a numeral) does not get stripped off before the message is issued to the various I/O handlers supported by kdb. This causes annoying visual noise as well as causing problems grepping for ^. It is also a change of behaviour compared to normal usage of printk() usage. For example <SysRq>-h ends up with different output to that of kdb's "sr h".
This patch addresses the problem by stripping log levels from messages before they are issued to the I/O handlers. printk() which can also act as an i/o handler in some cases is special cased; if the caller provided a log level then this will be preserved when sent to printk().
The addition of non-printable characters to the output of kdb commands is a regression, albeit and extremely elderly one, introduced by commit 04d2c8c83d0e ("printk: convert the format for KERN_<LEVEL> to a 2 byte pattern"). Note also that this patch does *not* restore the original behaviour from v3.5. Instead it makes printk() from within a kdb command display the message without any prefix (i.e. like printk() normally does).
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diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
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@@ -711,7 +712,10 @@ kdb_printit: if (logging) { saved_loglevel = console_loglevel; console_loglevel = CONSOLE_LOGLEVEL_SILENT;
printk(KERN_INFO "%s", kdb_buffer);
if (cp == kdb_buffer)printk(KERN_INFO "%s", kdb_buffer);elseprintk("%s", kdb_buffer);
The first part of the patch seem fine, but I'm confused about this bit above.
Here, isn't the "if (cp == kdb_buffer)" unnecessary?
if "(cp != kdb_buffer)", the buffer does have a prefix and it's emitted.
If (cp == kdb_buffer), the buffer does _not_ have a prefix (meaning it's either a naked printk or a continuation line. (KERN_CONT is "")
So why insert KERN_INFO?
I believe the code should be:
- printk(KERN_INFO "%s", kdb_buffer); + printk("%s", kdb_buffer);