Make common helpers for seq_files that work with list_heads

Many places in kernel use seq_file API to iterate over a regular list_head.
The code for such iteration is identical in all the places, so it's worth
introducing a common helpers.

This makes code about 300 lines smaller:

The first version of this patch made the helper functions static inline
in the seq_file.h header. This patch moves them to the fs/seq_file.c as
Andrew proposed. The vmlinux .text section sizes are as follows:

2.6.22-rc1-mm1:              0x001794d5
with the previous version:   0x00179505
with this patch:             0x00179135

The config file used was make allnoconfig with the "y" inclusion of all
the possible options to make the files modified by the patch compile plus
drivers I have on the test node.

This patch:

Many places in kernel use seq_file API to iterate over a regular list_head.
The code for such iteration is identical in all the places, so it's worth
introducing a common helpers.
Signed-off-by: NPavel Emelianov <xemul@openvz.org>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/seq_file.c

@@ -447,3 +447,37 @@ int seq_puts(struct seq_file *m, const char *s)
 	return -1;
 }
 EXPORT_SYMBOL(seq_puts);
+
+struct list_head *seq_list_start(struct list_head *head, loff_t pos)
+{
+	struct list_head *lh;
+
+	list_for_each(lh, head)
+		if (pos-- == 0)
+			return lh;
+
+	return NULL;
+}
+
+EXPORT_SYMBOL(seq_list_start);
+
+struct list_head *seq_list_start_head(struct list_head *head, loff_t pos)
+{
+	if (!pos)
+		return head;
+
+	return seq_list_start(head, pos - 1);
+}
+
+EXPORT_SYMBOL(seq_list_start_head);
+
+struct list_head *seq_list_next(void *v, struct list_head *head, loff_t *ppos)
+{
+	struct list_head *lh;
+
+	lh = ((struct list_head *)v)->next;
+	++*ppos;
+	return lh == head ? NULL : lh;
+}
+
+EXPORT_SYMBOL(seq_list_next);

include/linux/seq_file.h

@@ -50,5 +50,16 @@ int seq_release_private(struct inode *, struct file *);
 
 #define SEQ_START_TOKEN ((void *)1)
 
+/*
+ * Helpers for iteration over list_head-s in seq_files
+ */
+
+extern struct list_head *seq_list_start(struct list_head *head,
+		loff_t pos);
+extern struct list_head *seq_list_start_head(struct list_head *head,
+		loff_t pos);
+extern struct list_head *seq_list_next(void *v, struct list_head *head,
+		loff_t *ppos);
+
 #endif
 #endif