[PATCHSET] printk: implement printk_header() and merging printk

[Tejun Heo <htejun@gmail.com>]

Hello, all.

This patchset implements printk_header() and mprintk - merging printk
- to make printing multiline messages and assembling message
piece-by-piece easier.

In a nutshell, printk_header() lets you do the following atomically
(against other messages).

 code:
  printk(KERN_INFO "ata1.00: ", "line0\nline1\nline2\n");

 output:
  <6>ata1.00: line0
  <6>         line1
  <6>         line2

And mprintk the following.

 code:
  DEFINE_MPRINTK(mp, 2 * 80);

  mprintk_set_header(&mp, KERN_INFO "ata%u.%2u: ", 1, 0);
  mprintk_push(&mp, "ATA %d", 7);
  mprintk_push(&mp, ", %u sectors\n", 1024);
  mprintk(&mp, "everything seems dandy\n");

 output:
  <6>ata1.00: ATA 7, 1024 sectors
  <6>         everything seems dandy

Please read the commit messages and comments for more detail.  If this
patchset is accepted, I'll write up Documentation/printk.txt which
contains describtion of the API and guidelines - "don't pack unrelated
messages into one" kind of stuff.

This patchset is against the current linux-2.6#master (031f2dcd) and
contains the following patches.

0001-printk-keep-log-level-on-multiline-messages.patch
0002-printk-implement-v-printk_header.patch
0003-printk-implement-merging-printk.patch
0004-libata-make-libata-use-printk_header-and-mprintk.patch

 drivers/ata/libata-core.c   |  202 +++++++++++++++----------
 drivers/ata/libata-eh.c     |  150 ++++++++----------
 drivers/ata/libata-pmp.c    |    5 
 drivers/ata/libata-scsi.c   |    6 
 drivers/ata/sata_inic162x.c |    2 
 drivers/ata/sata_nv.c       |    4 
 include/linux/kernel.h      |   83 ++++++++++
 include/linux/libata.h      |   35 ++--
 kernel/printk.c             |  354 ++++++++++++++++++++++++++++++++++++++++----
 9 files changed, 630 insertions(+), 211 deletions(-)

More than half of the code increase in kernel.h are from the dummy
declarations for !CONFIG_PRINTK.  More than one third of printk.c
increase are comments.  On my x86-64 configuration, printk.o grows
from 30152 to 34128.

libata code grows slightly but the increase is from converting the
printk wrapper from #define to proper functions.  The converted areas
- device configuration and EH reporting - were reduced in comlexity
and size.  With all-y, drivers/ata/built-in.o shrinks from 726509 to
717657 mostly due to the conversion away from macros.

Thanks.

--
tejun