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

From: NeilBrown
Date: Wed Oct 08 2014 - 19:58:21 EST

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.



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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