new helper: iterate_supers()

... and switch the simple "loop over superblocks and do something"
loops to it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/buffer.c

@@ -560,25 +560,17 @@ static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 	return err;
 }
 
-static void do_thaw_all(struct work_struct *work)
+static void do_thaw_one(struct super_block *sb, void *unused)
 {
-	struct super_block *sb, *n;
 	char b[BDEVNAME_SIZE];
+	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
+		printk(KERN_WARNING "Emergency Thaw on %s\n",
+		       bdevname(sb->s_bdev, b));
+}
 
-	spin_lock(&sb_lock);
-	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
-		if (list_empty(&sb->s_instances))
-			continue;
-		sb->s_count++;
-		spin_unlock(&sb_lock);
-		down_read(&sb->s_umount);
-		while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
-			printk(KERN_WARNING "Emergency Thaw on %s\n",
-			       bdevname(sb->s_bdev, b));
-		up_read(&sb->s_umount);
-		spin_lock(&sb_lock);
-	}
-	spin_unlock(&sb_lock);
+static void do_thaw_all(struct work_struct *work)
+{
+	iterate_supers(do_thaw_one, NULL);
 	kfree(work);
 	printk(KERN_WARNING "Emergency Thaw complete\n");
 }

fs/drop_caches.c

@@ -8,12 +8,11 @@
 #include <linux/writeback.h>
 #include <linux/sysctl.h>
 #include <linux/gfp.h>
-#include "internal.h"
 
 /* A global variable is a bit ugly, but it keeps the code simple */
 int sysctl_drop_caches;
 
-static void drop_pagecache_sb(struct super_block *sb)
+static void drop_pagecache_sb(struct super_block *sb, void *unused)
 {
 	struct inode *inode, *toput_inode = NULL;
 
@@ -34,26 +33,6 @@ static void drop_pagecache_sb(struct super_block *sb)
 	iput(toput_inode);
 }
 
-static void drop_pagecache(void)
-{
-	struct super_block *sb, *n;
-
-	spin_lock(&sb_lock);
-	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
-		if (list_empty(&sb->s_instances))
-			continue;
-		sb->s_count++;
-		spin_unlock(&sb_lock);
-		down_read(&sb->s_umount);
-		if (sb->s_root)
-			drop_pagecache_sb(sb);
-		up_read(&sb->s_umount);
-		spin_lock(&sb_lock);
-		__put_super(sb);
-	}
-	spin_unlock(&sb_lock);
-}
-
 static void drop_slab(void)
 {
 	int nr_objects;
@@ -69,7 +48,7 @@ int drop_caches_sysctl_handler(ctl_table *table, int write,
 	proc_dointvec_minmax(table, write, buffer, length, ppos);
 	if (write) {
 		if (sysctl_drop_caches & 1)
-			drop_pagecache();
+			iterate_supers(drop_pagecache_sb, NULL);
 		if (sysctl_drop_caches & 2)
 			drop_slab();
 	}

fs/quota/quota.c

@@ -18,7 +18,6 @@
 #include <linux/quotaops.h>
 #include <linux/types.h>
 #include <linux/writeback.h>
-#include "../internal.h"
 
 static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
 				     qid_t id)
@@ -46,36 +45,22 @@ static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
 	return security_quotactl(cmd, type, id, sb);
 }
 
+static void quota_sync_one(struct super_block *sb, void *arg)
+{
+	if (sb->s_qcop && sb->s_qcop->quota_sync)
+		sb->s_qcop->quota_sync(sb, *(int *)arg, 1);
+}
+
 static int quota_sync_all(int type)
 {
-	struct super_block *sb, *n;
 	int ret;
 
 	if (type >= MAXQUOTAS)
 		return -EINVAL;
 	ret = security_quotactl(Q_SYNC, type, 0, NULL);
-	if (ret)
-		return ret;
-
-	spin_lock(&sb_lock);
-	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
-		if (list_empty(&sb->s_instances))
-			continue;
-		if (!sb->s_qcop || !sb->s_qcop->quota_sync)
-			continue;
-
-		sb->s_count++;
-		spin_unlock(&sb_lock);
-		down_read(&sb->s_umount);
-		if (sb->s_root)
-			sb->s_qcop->quota_sync(sb, type, 1);
-		up_read(&sb->s_umount);
-		spin_lock(&sb_lock);
-		__put_super(sb);
-	}
-	spin_unlock(&sb_lock);
-
-	return 0;
+	if (!ret)
+		iterate_supers(quota_sync_one, &type);
+	return ret;
 }
 
 static int quota_quotaon(struct super_block *sb, int type, int cmd, qid_t id,

fs/super.c

@@ -391,6 +391,36 @@ void sync_supers(void)
 	spin_unlock(&sb_lock);
 }
 
+/**
+ *	iterate_supers - call function for all active superblocks
+ *	@f: function to call
+ *	@arg: argument to pass to it
+ *
+ *	Scans the superblock list and calls given function, passing it
+ *	locked superblock and given argument.
+ */
+void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
+{
+	struct super_block *sb, *n;
+
+	spin_lock(&sb_lock);
+	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
+		if (list_empty(&sb->s_instances))
+			continue;
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		down_read(&sb->s_umount);
+		if (sb->s_root)
+			f(sb, arg);
+		up_read(&sb->s_umount);
+
+		spin_lock(&sb_lock);
+		__put_super(sb);
+	}
+	spin_unlock(&sb_lock);
+}
+
 /**
  *	get_super - get the superblock of a device
  *	@bdev: device to get the superblock for

fs/sync.c

@@ -77,31 +77,18 @@ int sync_filesystem(struct super_block *sb)
 }
 EXPORT_SYMBOL_GPL(sync_filesystem);
 
+static void sync_one_sb(struct super_block *sb, void *arg)
+{
+	if (!(sb->s_flags & MS_RDONLY) && sb->s_bdi)
+		__sync_filesystem(sb, *(int *)arg);
+}
 /*
  * Sync all the data for all the filesystems (called by sys_sync() and
  * emergency sync)
  */
 static void sync_filesystems(int wait)
 {
-	struct super_block *sb, *n;
-
-	spin_lock(&sb_lock);
-	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
-		if (list_empty(&sb->s_instances))
-			continue;
-		sb->s_count++;
-		spin_unlock(&sb_lock);
-
-		down_read(&sb->s_umount);
-		if (!(sb->s_flags & MS_RDONLY) && sb->s_root && sb->s_bdi)
-			__sync_filesystem(sb, wait);
-		up_read(&sb->s_umount);
-
-		/* restart only when sb is no longer on the list */
-		spin_lock(&sb_lock);
-		__put_super(sb);
-	}
-	spin_unlock(&sb_lock);
+	iterate_supers(sync_one_sb, &wait);
 }
 
 /*

include/linux/fs.h

@@ -2324,6 +2324,7 @@ extern struct super_block *get_super(struct block_device *);
 extern struct super_block *get_active_super(struct block_device *bdev);
 extern struct super_block *user_get_super(dev_t);
 extern void drop_super(struct super_block *sb);
+extern void iterate_supers(void (*)(struct super_block *, void *), void *);
 
 extern int dcache_dir_open(struct inode *, struct file *);
 extern int dcache_dir_close(struct inode *, struct file *);