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 <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Stefano Brivio <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: "Ma, Jianpeng" <[email protected]>
Cc: Yury Norov <[email protected]>
Cc: Valentin Schneider <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Daniel Bristot de Oliveira <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Signed-off-by: Tian Tao <[email protected]>
Signed-off-by: Barry Song <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Tian Tao

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)))
 

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) { {								\

lib/bitmap.c

@@ -487,6 +487,109 @@ int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
 }
 EXPORT_SYMBOL(bitmap_print_to_pagebuf);
 
+/**
+ * bitmap_print_to_buf  - convert bitmap to list or hex format ASCII string
+ * @list: indicates whether the bitmap must be list
+ *      true:  print in decimal list format
+ *      false: print in hexadecimal bitmask format
+ */
+static int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp,
+		int nmaskbits, loff_t off, size_t count)
+{
+	const char *fmt = list ? "%*pbl\n" : "%*pb\n";
+	ssize_t size;
+	void *data;
+
+	data = kasprintf(GFP_KERNEL, fmt, nmaskbits, maskp);
+	if (!data)
+		return -ENOMEM;
+
+	size = memory_read_from_buffer(buf, count, &off, data, strlen(data) + 1);
+	kfree(data);
+
+	return size;
+}
+
+/**
+ * bitmap_print_bitmask_to_buf  - convert bitmap to hex bitmask format ASCII string
+ *
+ * The bitmap_print_to_pagebuf() is used indirectly via its cpumap wrapper
+ * cpumap_print_to_pagebuf() or directly by drivers to export hexadecimal
+ * bitmask and decimal list to userspace by sysfs ABI.
+ * Drivers might be using a normal attribute for this kind of ABIs. A
+ * normal attribute typically has show entry as below:
+ * static ssize_t example_attribute_show(struct device *dev,
+ * 		struct device_attribute *attr, char *buf)
+ * {
+ * 	...
+ * 	return bitmap_print_to_pagebuf(true, buf, &mask, nr_trig_max);
+ * }
+ * show entry of attribute has no offset and count parameters and this
+ * means the file is limited to one page only.
+ * bitmap_print_to_pagebuf() API works terribly well for this kind of
+ * normal attribute with buf parameter and without offset, count:
+ * bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
+ * 			   int nmaskbits)
+ * {
+ * }
+ * The problem is once we have a large bitmap, we have a chance to get a
+ * 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.
+ * bitmap_print_bitmask_to_buf(), bitmap_print_list_to_buf() wit their
+ * cpumap wrapper cpumap_print_bitmask_to_buf(), cpumap_print_list_to_buf()
+ * make those drivers be able to support large bitmask and list after they
+ * move to use bin_attribute. In result, we have to pass the corresponding
+ * parameters such as off, count from bin_attribute show entry to this API.
+ *
+ * @buf: buffer into which string is placed
+ * @maskp: pointer to bitmap to convert
+ * @nmaskbits: size of bitmap, in bits
+ * @off: in the string from which we are copying, We copy to @buf
+ * @count: the maximum number of bytes to print
+ *
+ * The role of cpumap_print_bitmask_to_buf() and cpumap_print_list_to_buf()
+ * is similar with cpumap_print_to_pagebuf(),  the difference is that
+ * bitmap_print_to_pagebuf() mainly serves sysfs attribute with the assumption
+ * the destination buffer is exactly one page and won't be more than one page.
+ * cpumap_print_bitmask_to_buf() and cpumap_print_list_to_buf(), on the other
+ * hand, mainly serves bin_attribute which doesn't work with exact one page,
+ * and it can break the size limit of converted decimal list and hexadecimal
+ * bitmask.
+ *
+ * Returns the number of characters actually printed to @buf
+ */
+int bitmap_print_bitmask_to_buf(char *buf, const unsigned long *maskp,
+				int nmaskbits, loff_t off, size_t count)
+{
+	return bitmap_print_to_buf(false, buf, maskp, nmaskbits, off, count);
+}
+EXPORT_SYMBOL(bitmap_print_bitmask_to_buf);
+
+/**
+ * bitmap_print_list_to_buf  - convert bitmap to decimal list format ASCII string
+ *
+ * Everything is same with the above bitmap_print_bitmask_to_buf() except
+ * the print format.
+ */
+int bitmap_print_list_to_buf(char *buf, const unsigned long *maskp,
+			     int nmaskbits, loff_t off, size_t count)
+{
+	return bitmap_print_to_buf(true, buf, maskp, nmaskbits, off, count);
+}
+EXPORT_SYMBOL(bitmap_print_list_to_buf);
+
 /*
  * Region 9-38:4/10 describes the following bitmap structure:
  * 0	   9  12    18			38	     N