Commit a5e112e6 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: add cgroup_parse_float() 



cgroup already uses floating point for percent[ile] numbers and there
are several controllers which want to take them as input.  Add a
generic parse helper to handle inputs.

Update the interface convention documentation about the use of
percentage numbers.  While at it, also clarify the default time unit.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent c03cd773

Documentation/admin-guide/cgroup-v2.rst

+6 −0
Original line number Diff line number Diff line
@@ -696,6 +696,12 @@ Conventions 
  informational files on the root cgroup which end up showing global

  information available elsewhere shouldn't exist.



- The default time unit is microseconds.  If a different unit is ever

  used, an explicit unit suffix must be present.



- A parts-per quantity should use a percentage decimal with at least

  two digit fractional part - e.g. 13.40.



- If a controller implements weight based resource distribution, its

  interface file should be named "weight" and have the range [1,

  10000] with 100 as the default.  The values are chosen to allow

include/linux/cgroup.h

+2 −0
Original line number Diff line number Diff line
@@ -131,6 +131,8 @@ void cgroup_free(struct task_struct *p); 
int cgroup_init_early(void);

int cgroup_init(void);



int cgroup_parse_float(const char *input, unsigned dec_shift, s64 *v);



/*

 * Iteration helpers and macros.

 */

kernel/cgroup/cgroup.c

+43 −0
Original line number Diff line number Diff line
@@ -6387,4 +6387,47 @@ static int __init cgroup_sysfs_init(void) 
	return sysfs_create_group(kernel_kobj, &cgroup_sysfs_attr_group);

}

subsys_initcall(cgroup_sysfs_init);



static u64 power_of_ten(int power)

{

	u64 v = 1;

	while (power--)

		v *= 10;

	return v;

}



/**

 * cgroup_parse_float - parse a floating number

 * @input: input string

 * @dec_shift: number of decimal digits to shift

 * @v: output

 *

 * Parse a decimal floating point number in @input and store the result in

 * @v with decimal point right shifted @dec_shift times.  For example, if

 * @input is "12.3456" and @dec_shift is 3, *@v will be set to 12345.

 * Returns 0 on success, -errno otherwise.

 *

 * There's nothing cgroup specific about this function except that it's

 * currently the only user.

 */

int cgroup_parse_float(const char *input, unsigned dec_shift, s64 *v)

{

	s64 whole, frac = 0;

	int fstart = 0, fend = 0, flen;



	if (!sscanf(input, "%lld.%n%lld%n", &whole, &fstart, &frac, &fend))

		return -EINVAL;

	if (frac < 0)

		return -EINVAL;



	flen = fend > fstart ? fend - fstart : 0;

	if (flen < dec_shift)

		frac *= power_of_ten(dec_shift - flen);

	else

		frac = DIV_ROUND_CLOSEST_ULL(frac, power_of_ten(flen - dec_shift));



	*v = whole * power_of_ten(dec_shift) + frac;

	return 0;

}



#endif /* CONFIG_SYSFS */

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