seq_file: add seq_cpumask(), seq_nodemask()

Short enough reads from /proc/irq/*/smp_affinity return -EINVAL for no
good reason.

This became noticed with NR_CPUS=4096 patches, when length of printed
representation of cpumask becase 1152, but cat(1) continued to read with
1024-byte chunks.  bitmap_scnprintf() in good faith fills buffer, returns
1023, check returns -EINVAL.

Fix it by switching to seq_file, so handler will just fill buffer and
doesn't care about offsets, length, filling EOF and all this crap.

For that add seq_bitmap(), and wrappers around it -- seq_cpumask() and
seq_nodemask().
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Paul Jackson <pj@sgi.com>
Cc: Mike Travis <travis@sgi.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/seq_file.c

@@ -443,6 +443,20 @@ int seq_dentry(struct seq_file *m, struct dentry *dentry, char *esc)
 	return -1;
 }
 
+int seq_bitmap(struct seq_file *m, unsigned long *bits, unsigned int nr_bits)
+{
+	size_t len = bitmap_scnprintf_len(nr_bits);
+
+	if (m->count + len < m->size) {
+		bitmap_scnprintf(m->buf + m->count, m->size - m->count,
+				 bits, nr_bits);
+		m->count += len;
+		return 0;
+	}
+	m->count = m->size;
+	return -1;
+}
+
 static void *single_start(struct seq_file *p, loff_t *pos)
 {
 	return NULL + (*pos == 0);

include/linux/bitmap.h

@@ -110,6 +110,7 @@ extern int __bitmap_weight(const unsigned long *bitmap, int bits);
 
 extern int bitmap_scnprintf(char *buf, unsigned int len,
 			const unsigned long *src, int nbits);
+extern int bitmap_scnprintf_len(unsigned int nr_bits);
 extern int __bitmap_parse(const char *buf, unsigned int buflen, int is_user,
 			unsigned long *dst, int nbits);
 extern int bitmap_parse_user(const char __user *ubuf, unsigned int ulen,

include/linux/seq_file.h

@@ -4,6 +4,8 @@
 #include <linux/types.h>
 #include <linux/string.h>
 #include <linux/mutex.h>
+#include <linux/cpumask.h>
+#include <linux/nodemask.h>
 
 struct seq_operations;
 struct file;
@@ -47,6 +49,16 @@ int seq_path(struct seq_file *, struct path *, char *);
 int seq_dentry(struct seq_file *, struct dentry *, char *);
 int seq_path_root(struct seq_file *m, struct path *path, struct path *root,
 		  char *esc);
+int seq_bitmap(struct seq_file *m, unsigned long *bits, unsigned int nr_bits);
+static inline int seq_cpumask(struct seq_file *m, cpumask_t *mask)
+{
+	return seq_bitmap(m, mask->bits, NR_CPUS);
+}
+
+static inline int seq_nodemask(struct seq_file *m, nodemask_t *mask)
+{
+	return seq_bitmap(m, mask->bits, MAX_NUMNODES);
+}
 
 int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
 int single_release(struct inode *, struct file *);

lib/bitmap.c

@@ -315,6 +315,17 @@ int bitmap_scnprintf(char *buf, unsigned int buflen,
 }
 EXPORT_SYMBOL(bitmap_scnprintf);
 
+/**
+ * bitmap_scnprintf_len - return buffer length needed to convert
+ * bitmap to an ASCII hex string
+ * @nr_bits: number of bits to be converted
+ */
+int bitmap_scnprintf_len(unsigned int nr_bits)
+{
+	unsigned int nr_nibbles = ALIGN(nr_bits, 4) / 4;
+	return nr_nibbles + ALIGN(nr_nibbles, CHUNKSZ / 4) / (CHUNKSZ / 4) - 1;
+}
+
 /**
  * __bitmap_parse - convert an ASCII hex string into a bitmap.
  * @buf: pointer to buffer containing string.