[PATCH v2 1/3] lib: bitmap: introduce bitmap_print_to_buf

[Tian Tao]

New API bitmap_print_to_buf() with bin_attribute to avoid maskp
exceeding PAGE_SIZE. bitmap_print_to_pagebuf() is a special case
of bitmap_print_to_buf(), so in bitmap_print_to_pagebuf() call
bitmap_print_to_buf().

Signed-off-by: Tian Tao <tiantao6@xxxxxxxxxxxxx>
---
 include/linux/bitmap.h  |  3 +++
 include/linux/cpumask.h | 21 +++++++++++++++++++++
 lib/bitmap.c            | 38 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 70a9324..bc401bd9b 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -219,6 +219,9 @@ extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned int
 extern int bitmap_print_to_pagebuf(bool list, char *buf,
 				   const unsigned long *maskp, int nmaskbits);
 
+extern int bitmap_print_to_buf(bool list, 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 383684e..56852f2 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -928,6 +928,27 @@ cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask)
 				      nr_cpu_ids);
 }
 
+/**
+ * cpumap_print_to_buf  - copies the cpumask into the buffer either
+ *      as comma-separated list of cpus or hex values of cpumask
+ * @list: indicates whether the cpumap must be list
+ * @mask: the cpumask to copy
+ * @buf: the buffer to copy into
+ * @off: in the string from which we are copying, We copy to @buf + off
+ * @count: the maximum number of bytes to print
+ *
+ * The role of cpumap_print_to_buf and cpumap_print_to_pagebuf is
+ * the same, the difference is that buf of bitmap_print_to_buf
+ * can be more than one pagesize.
+ */
+static inline ssize_t
+cpumap_print_to_buf(bool list, char *buf, const struct cpumask *mask,
+		    loff_t off, size_t count)
+{
+	return bitmap_print_to_buf(list, buf, cpumask_bits(mask),
+				   nr_cpu_ids, off, count);
+}
+
 #if NR_CPUS <= BITS_PER_LONG
 #define CPU_MASK_ALL							\
 (cpumask_t) { {								\
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 75006c4..cb64e66 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -460,6 +460,40 @@ int bitmap_parse_user(const char __user *ubuf,
 EXPORT_SYMBOL(bitmap_parse_user);
 
 /**
+ * bitmap_print_to_buf - convert bitmap to list or hex format ASCII string
+ * @list: indicates whether the bitmap must be list
+ * @buf: the kernel space buffer to read to
+ * @maskp: pointer to bitmap to convert
+ * @nmaskbits: size of bitmap, in bits
+ * @off: offset in data buffer below
+ * @count: the maximum number of bytes to print
+ *
+ * The role of bitmap_print_to_buf and bitmap_print_to_pagebuf() is
+ * the same, the difference is that buf of bitmap_print_to_buf()
+ * can be more than one pagesize.
+ */
+int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp,
+			int nmaskbits, loff_t off, size_t count)
+{
+	int size;
+	void *data;
+	const char *fmt = list ? "%*pbl\n" : "%*pb\n";
+
+	if (off == LLONG_MAX && count == PAGE_SIZE - offset_in_page(buf))
+		return scnprintf(buf, count, fmt, nmaskbits, maskp);
+
+	data = kasprintf(GFP_KERNEL, fmt, nmaskbits, maskp);
+	if (!data)
+		return -ENOMEM;
+
+	size = memory_read_from_buffer(buf, count, &off, data, strlen(data));
+	kfree(data);
+
+	return size;
+}
+EXPORT_SYMBOL(bitmap_print_to_buf);
+
+/**
  * bitmap_print_to_pagebuf - convert bitmap to list or hex format ASCII string
  * @list: indicates whether the bitmap must be list
  * @buf: page aligned buffer into which string is placed
@@ -480,8 +514,8 @@ int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
 {
 	ptrdiff_t len = PAGE_SIZE - offset_in_page(buf);
 
-	return list ? scnprintf(buf, len, "%*pbl\n", nmaskbits, maskp) :
-		      scnprintf(buf, len, "%*pb\n", nmaskbits, maskp);
+	return bitmap_print_to_buf(list, buf, maskp, nmaskbits,
+				   LLONG_MAX, len);
 }
 EXPORT_SYMBOL(bitmap_print_to_pagebuf);
 
-- 
2.7.4