quota: Implement function for scanning active dquots

OCFS2 needs to scan all active dquots once in a while and sync quota
information among cluster nodes. Provide a helper function for it so
that it does not have to reimplement internally a list which VFS
already has. Moreover this function is probably going to be useful
for other clustered filesystems if they decide to use VFS quotas.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

2 files changed, 39 insertions, 0 deletions

diff --git a/fs/dquot.c b/fs/dquot.c
index ae8fd9e645cc..075dc76904e7 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -476,6 +476,41 @@ restart:
         spin_unlock(&dq_list_lock);
 }
 
+/* Call callback for every active dquot on given filesystem */
+int dquot_scan_active(struct super_block *sb,
+                      int (*fn)(struct dquot *dquot, unsigned long priv),
+                      unsigned long priv)
+{
+        struct dquot *dquot, *old_dquot = NULL;
+        int ret = 0;
+
+        mutex_lock(&sb_dqopt(sb)->dqonoff_mutex);
+        spin_lock(&dq_list_lock);
+        list_for_each_entry(dquot, &inuse_list, dq_inuse) {
+                if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
+                        continue;
+                if (dquot->dq_sb != sb)
+                        continue;
+                /* Now we have active dquot so we can just increase use count */
+                atomic_inc(&dquot->dq_count);
+                dqstats.lookups++;
+                spin_unlock(&dq_list_lock);
+                dqput(old_dquot);
+                old_dquot = dquot;
+                ret = fn(dquot, priv);
+                if (ret < 0)
+                        goto out;
+                spin_lock(&dq_list_lock);
+                /* We are safe to continue now because our dquot could not
+                 * be moved out of the inuse list while we hold the reference */
+        }
+        spin_unlock(&dq_list_lock);
+out:
+        dqput(old_dquot);
+        mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
+        return ret;
+}
+
 int vfs_quota_sync(struct super_block *sb, int type)
 {
         struct list_head *dirty;
@@ -2318,6 +2353,7 @@ EXPORT_SYMBOL(vfs_quota_on_path);
 EXPORT_SYMBOL(vfs_quota_on_mount);
 EXPORT_SYMBOL(vfs_quota_disable);
 EXPORT_SYMBOL(vfs_quota_off);
+EXPORT_SYMBOL(dquot_scan_active);
 EXPORT_SYMBOL(vfs_quota_sync);
 EXPORT_SYMBOL(vfs_get_dqinfo);
 EXPORT_SYMBOL(vfs_set_dqinfo);
diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
index e3a10272d471..f4913948c305 100644
--- a/include/linux/quotaops.h
+++ b/include/linux/quotaops.h
@@ -28,6 +28,9 @@ int dquot_drop_locked(struct inode *inode);
 struct dquot *dqget(struct super_block *sb, unsigned int id, int type);
 void dqput(struct dquot *dquot);
 int dquot_is_cached(struct super_block *sb, unsigned int id, int type);
+int dquot_scan_active(struct super_block *sb,
+                      int (*fn)(struct dquot *dquot, unsigned long priv),
+                      unsigned long priv);
 
 int dquot_alloc_space(struct inode *inode, qsize_t number, int prealloc);
 int dquot_alloc_inode(const struct inode *inode, qsize_t number);