cpumask: introduce cpumap_print_list/bitmask_to_buf to support large bitmask and list

The existing cpumap_print_to_pagebuf() is used by cpu topology and other
drivers to export hexadecimal bitmask and decimal list to userspace by
sysfs ABI.

Right now, those drivers are using a normal attribute for this kind of
ABIs. A normal attribute typically has show entry as below:

static ssize_t example_dev_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
	...
	return cpumap_print_to_pagebuf(true, buf, &pmu_mmdc->cpu);
}
show entry of attribute has no offset and count parameters and this
means the file is limited to one page only.

cpumap_print_to_pagebuf() API works terribly well for this kind of
normal attribute with buf parameter and without offset, count:

static inline ssize_t
cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask)
{
	return bitmap_print_to_pagebuf(list, buf, cpumask_bits(mask),
				       nr_cpu_ids);
}

The problem is once we have many cpus, we have a chance to make bitmask
or list more than one page. Especially for list, it could be as complex
as 0,3,5,7,9,...... We have no simple way to know it exact size.

It turns out bin_attribute is a way to break this limit. bin_attribute
has show entry as below:
static ssize_t
example_bin_attribute_show(struct file *filp, struct kobject *kobj,
             struct bin_attribute *attr, char *buf,
             loff_t offset, size_t count)
{
	...
}

With the new offset and count parameters, this makes sysfs ABI be able
to support file size more than one page. For example, offset could be
>= 4096.

This patch introduces cpumap_print_bitmask/list_to_buf() and their bitmap
infrastructure bitmap_print_bitmask/list_to_buf() so that those drivers
can move to bin_attribute to support large bitmask and list. At the same
time, we have to pass those corresponding parameters such as offset, count
from bin_attribute to this new API.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stefano Brivio <sbrivio@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: "Ma, Jianpeng" <jianpeng.ma@intel.com>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Link: https://lore.kernel.org/r/20210806110251.560-2-song.bao.hua@hisilicon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 44 insertions, 0 deletions

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index a36cfcec4e77..37f36dad18bd 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -227,6 +227,12 @@ unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned int ord, un
 int bitmap_print_to_pagebuf(bool list, char *buf,
 				   const unsigned long *maskp, int nmaskbits);
 
+extern int bitmap_print_bitmask_to_buf(char *buf, const unsigned long *maskp,
+				      int nmaskbits, loff_t off, size_t count);
+
+extern int bitmap_print_list_to_buf(char *buf, const unsigned long *maskp,
+				      int nmaskbits, loff_t off, size_t count);
+
 #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
 #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
 
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index f3689a52bfd0..5d4d07a9e1ed 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -983,6 +983,44 @@ cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask)
 				      nr_cpu_ids);
 }
 
+/**
+ * cpumap_print_bitmask_to_buf  - copies the cpumask into the buffer as
+ *	hex values of cpumask
+ *
+ * @buf: the buffer to copy into
+ * @mask: the cpumask to copy
+ * @off: in the string from which we are copying, we copy to @buf
+ * @count: the maximum number of bytes to print
+ *
+ * The function prints the cpumask into the buffer as hex values of
+ * cpumask; Typically used by bin_attribute to export cpumask bitmask
+ * ABI.
+ *
+ * Returns the length of how many bytes have been copied.
+ */
+static inline ssize_t
+cpumap_print_bitmask_to_buf(char *buf, const struct cpumask *mask,
+		loff_t off, size_t count)
+{
+	return bitmap_print_bitmask_to_buf(buf, cpumask_bits(mask),
+				   nr_cpu_ids, off, count);
+}
+
+/**
+ * cpumap_print_list_to_buf  - copies the cpumask into the buffer as
+ *	comma-separated list of cpus
+ *
+ * Everything is same with the above cpumap_print_bitmask_to_buf()
+ * except the print format.
+ */
+static inline ssize_t
+cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
+		loff_t off, size_t count)
+{
+	return bitmap_print_list_to_buf(buf, cpumask_bits(mask),
+				   nr_cpu_ids, off, count);
+}
+
 #if NR_CPUS <= BITS_PER_LONG
 #define CPU_MASK_ALL							\
 (cpumask_t) { {								\