start switching sysfs attributes to expose the seq_file

[Christoph Hellwig]

Hi all,

Al pointed out multiple times that seq_get_buf is highly dangerous as
it opens up the tight seq_file abstractions to buffer overflows.  The
last such caller now is sysfs.

This series allows attributes to implement a seq_show method and switch
the block and XFS code as users that I'm most familiar with to use
seq_files directly after a few preparatory cleanups.  With this series
"leaf" users of sysfs_ops can be converted one at at a time, after that
we can move the seq_get_buf into the multiplexers (e.g. kobj, device,
class attributes) and remove the show method in sysfs_ops and repeat the
process until all attributes are converted.  This will probably take a
fair amount of time.

Diffstat:
 block/bfq-iosched.c      |   12 +-
 block/blk-integrity.c    |   44 +++++----
 block/blk-mq-sysfs.c     |   64 ++++++--------
 block/blk-sysfs.c        |  209 ++++++++++++++++++++++++++---------------------
 block/blk-throttle.c     |    5 -
 block/blk.h              |    2 
 block/elevator.c         |   42 +++++----
 block/kyber-iosched.c    |    7 -
 block/mq-deadline.c      |    5 -
 fs/sysfs/file.c          |  135 +++++++++++++++++-------------
 fs/sysfs/group.c         |   15 +--
 fs/sysfs/sysfs.h         |    8 +
 fs/xfs/xfs_error.c       |   14 +--
 fs/xfs/xfs_stats.c       |   24 ++---
 fs/xfs/xfs_stats.h       |    2 
 fs/xfs/xfs_sysfs.c       |   96 ++++++++++-----------
 include/linux/elevator.h |    4 
 include/linux/kernfs.h   |   28 ------
 include/linux/seq_file.h |    4 
 include/linux/sysfs.h    |    9 +-
 20 files changed, 376 insertions(+), 353 deletions(-)