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cgroup: update the meaning of cftype->max_write_len

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cftype->max_write_len is used to extend the maximum size of writes.
It's interpreted in such a way that the actual maximum size is one
less than the specified value.  The default size is defined by
CGROUP_LOCAL_BUFFER_SIZE.  Its interpretation is quite confusing - its
value is decremented by 1 and then compared for equality with max
size, which means that the actual default size is
CGROUP_LOCAL_BUFFER_SIZE - 2, which is 62 chars.

There's no point in having a limit that low.  Update its definition so
that it means the actual string length sans termination and anything
below PAGE_SIZE-1 is treated as PAGE_SIZE-1.

.max_write_len for "release_agent" is updated to PATH_MAX-1 and
cgroup_release_agent_write() is updated so that the redundant strlen()
check is removed and it uses strlcpy() instead of strcpy().
.max_write_len initializations in blk-throttle.c and cfq-iosched.c are
no longer necessary and removed.  The one in cpuset is kept unchanged
as it's an approximated value to begin with.

This will also make transition to kernfs smoother.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2014-02-11 11:52:48 -05:00
parent de00ffa56e
commit 5f46990787
4 changed files with 11 additions and 19 deletions
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5
include/linux/cgroup.h
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@ -400,8 +400,9 @@ struct cftype {
umode_t mode;
/*
* If non-zero, defines the maximum length of string that can
* be passed to write_string; defaults to 64
* The maximum length of string, excluding trailing nul, that can
* be passed to write_string. If < PAGE_SIZE-1, PAGE_SIZE-1 is
* assumed.
*/
size_t max_write_len;