[PATCH 0/2 V2] Allow access to sysfs attributes without mem allocations.

[NeilBrown]

Hi Tejun,
 thanks for the review.  This version incorporates your suggestions.

 You are certainly right about there being issues deeper than just the
 sysfs/kernfs level - I've been cleaning up the locking in md to avoid
 the "reconfig_mutex" as much as possible.  It is something that has
 been at the back of my mind for a while, but this need has pushed it
 to the fore-front.  All the attributes that mdmon needs to touch will
 soon only take a spinlock or nothing.

 On the topic of inadvertently locking in semantics, I noticed that
 prior to kernfs, sysfs would allocate a buffer on first read or
 write, and continue to use that buffer.  I could try to argue that I
 was using those semantics, which have now changed ... though I wasn't
 doing it consciously...  Certainly this is a thorny issue.

 As well as checking that ->seq_show isn't used with ->prealloc,
 I've also made sure that sysfs_kf_read() doesn't call the attribute
 ->show() function unless it is certain it has a preallocated (and
 hence >= PAGE_SIZE) buffer.

Thanks,
NeilBrown

---

NeilBrown (2):
      sysfs/kernfs: allow attributes to request write buffer be pre-allocated.
      sysfs/kernfs: make read requests on pre-alloc files use the buffer.


 fs/kernfs/file.c       |   70 ++++++++++++++++++++++++++++++++----------------
 fs/sysfs/file.c        |   53 +++++++++++++++++++++++++++++++-----
 include/linux/kernfs.h |    2 +
 include/linux/sysfs.h  |    9 ++++++
 4 files changed, 103 insertions(+), 31 deletions(-)

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