Btrfs: rescan for qgroups

If qgroup tracking is out of sync, a rescan operation can be started. It
iterates the complete extent tree and recalculates all qgroup tracking data.
This is an expensive operation and should not be used unless required.

A filesystem under rescan can still be umounted. The rescan continues on the
next mount.  Status information is provided with a separate ioctl while a
rescan operation is in progress.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

5 files changed, 400 insertions, 35 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2c48f52aba40..d9bed5fd3347 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1021,9 +1021,9 @@ struct btrfs_block_group_item {
  */
 #define BTRFS_QGROUP_STATUS_FLAG_ON             (1ULL << 0)
 /*
- * SCANNING is set during the initialization phase
+ * RESCAN is set during the initialization phase
  */
-#define BTRFS_QGROUP_STATUS_FLAG_SCANNING       (1ULL << 1)
+#define BTRFS_QGROUP_STATUS_FLAG_RESCAN         (1ULL << 1)
 /*
  * Some qgroup entries are known to be out of date,
  * either because the configuration has changed in a way that
@@ -1052,7 +1052,7 @@ struct btrfs_qgroup_status_item {
          * only used during scanning to record the progress
          * of the scan. It contains a logical address
          */
-        __le64 scan;
+        __le64 rescan;
 } __attribute__ ((__packed__));
 
 struct btrfs_qgroup_info_item {
@@ -1603,6 +1603,11 @@ struct btrfs_fs_info {
         /* used by btrfs_qgroup_record_ref for an efficient tree traversal */
         u64 qgroup_seq;
 
+        /* qgroup rescan items */
+        struct mutex qgroup_rescan_lock; /* protects the progress item */
+        struct btrfs_key qgroup_rescan_progress;
+        struct btrfs_workers qgroup_rescan_workers;
+
         /* filesystem state */
         unsigned long fs_state;
 
@@ -2886,8 +2891,8 @@ BTRFS_SETGET_FUNCS(qgroup_status_version, struct btrfs_qgroup_status_item,
                    version, 64);
 BTRFS_SETGET_FUNCS(qgroup_status_flags, struct btrfs_qgroup_status_item,
                    flags, 64);
-BTRFS_SETGET_FUNCS(qgroup_status_scan, struct btrfs_qgroup_status_item,
-                   scan, 64);
+BTRFS_SETGET_FUNCS(qgroup_status_rescan, struct btrfs_qgroup_status_item,
+                   rescan, 64);
 
 /* btrfs_qgroup_info_item */
 BTRFS_SETGET_FUNCS(qgroup_info_generation, struct btrfs_qgroup_info_item,
@@ -3828,7 +3833,7 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
                        struct btrfs_fs_info *fs_info);
 int btrfs_quota_disable(struct btrfs_trans_handle *trans,
                         struct btrfs_fs_info *fs_info);
-int btrfs_quota_rescan(struct btrfs_fs_info *fs_info);
+int btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info);
 int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans,
                               struct btrfs_fs_info *fs_info, u64 src, u64 dst);
 int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 92c44ed78de1..d96305e5cc93 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1976,6 +1976,7 @@ static void btrfs_stop_all_workers(struct btrfs_fs_info *fs_info)
         btrfs_stop_workers(&fs_info->caching_workers);
         btrfs_stop_workers(&fs_info->readahead_workers);
         btrfs_stop_workers(&fs_info->flush_workers);
+        btrfs_stop_workers(&fs_info->qgroup_rescan_workers);
 }
 
 /* helper to cleanup tree roots */
@@ -2267,6 +2268,7 @@ int open_ctree(struct super_block *sb,
         fs_info->qgroup_seq = 1;
         fs_info->quota_enabled = 0;
         fs_info->pending_quota_state = 0;
+        mutex_init(&fs_info->qgroup_rescan_lock);
 
         btrfs_init_free_cluster(&fs_info->meta_alloc_cluster);
         btrfs_init_free_cluster(&fs_info->data_alloc_cluster);
@@ -2476,6 +2478,8 @@ int open_ctree(struct super_block *sb,
         btrfs_init_workers(&fs_info->readahead_workers, "readahead",
                            fs_info->thread_pool_size,
                            &fs_info->generic_worker);
+        btrfs_init_workers(&fs_info->qgroup_rescan_workers, "qgroup-rescan", 1,
+                           &fs_info->generic_worker);
 
         /*
          * endios are largely parallel and should have a very
@@ -2510,6 +2514,7 @@ int open_ctree(struct super_block *sb,
         ret |= btrfs_start_workers(&fs_info->caching_workers);
         ret |= btrfs_start_workers(&fs_info->readahead_workers);
         ret |= btrfs_start_workers(&fs_info->flush_workers);
+        ret |= btrfs_start_workers(&fs_info->qgroup_rescan_workers);
         if (ret) {
                 err = -ENOMEM;
                 goto fail_sb_buffer;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a74edc797531..f5f6af338b53 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3701,12 +3701,10 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
         }
 
         down_write(&root->fs_info->subvol_sem);
-        if (sa->cmd != BTRFS_QUOTA_CTL_RESCAN) {
-                trans = btrfs_start_transaction(root->fs_info->tree_root, 2);
-                if (IS_ERR(trans)) {
-                        ret = PTR_ERR(trans);
-                        goto out;
-                }
+        trans = btrfs_start_transaction(root->fs_info->tree_root, 2);
+        if (IS_ERR(trans)) {
+                ret = PTR_ERR(trans);
+                goto out;
         }
 
         switch (sa->cmd) {
@@ -3716,9 +3714,6 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
         case BTRFS_QUOTA_CTL_DISABLE:
                 ret = btrfs_quota_disable(trans, root->fs_info);
                 break;
-        case BTRFS_QUOTA_CTL_RESCAN:
-                ret = btrfs_quota_rescan(root->fs_info);
-                break;
         default:
                 ret = -EINVAL;
                 break;
@@ -3727,11 +3722,9 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
         if (copy_to_user(arg, sa, sizeof(*sa)))
                 ret = -EFAULT;
 
-        if (trans) {
-                err = btrfs_commit_transaction(trans, root->fs_info->tree_root);
-                if (err && !ret)
-                        ret = err;
-        }
+        err = btrfs_commit_transaction(trans, root->fs_info->tree_root);
+        if (err && !ret)
+                ret = err;
 out:
         kfree(sa);
         up_write(&root->fs_info->subvol_sem);
@@ -3886,6 +3879,64 @@ drop_write:
         return ret;
 }
 
+static long btrfs_ioctl_quota_rescan(struct file *file, void __user *arg)
+{
+        struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+        struct btrfs_ioctl_quota_rescan_args *qsa;
+        int ret;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        ret = mnt_want_write_file(file);
+        if (ret)
+                return ret;
+
+        qsa = memdup_user(arg, sizeof(*qsa));
+        if (IS_ERR(qsa)) {
+                ret = PTR_ERR(qsa);
+                goto drop_write;
+        }
+
+        if (qsa->flags) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        ret = btrfs_qgroup_rescan(root->fs_info);
+
+out:
+        kfree(qsa);
+drop_write:
+        mnt_drop_write_file(file);
+        return ret;
+}
+
+static long btrfs_ioctl_quota_rescan_status(struct file *file, void __user *arg)
+{
+        struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+        struct btrfs_ioctl_quota_rescan_args *qsa;
+        int ret = 0;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        qsa = kzalloc(sizeof(*qsa), GFP_NOFS);
+        if (!qsa)
+                return -ENOMEM;
+
+        if (root->fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) {
+                qsa->flags = 1;
+                qsa->progress = root->fs_info->qgroup_rescan_progress.objectid;
+        }
+
+        if (copy_to_user(arg, qsa, sizeof(*qsa)))
+                ret = -EFAULT;
+
+        kfree(qsa);
+        return ret;
+}
+
 static long btrfs_ioctl_set_received_subvol(struct file *file,
                                             void __user *arg)
 {
@@ -4124,6 +4175,10 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_qgroup_create(file, argp);
         case BTRFS_IOC_QGROUP_LIMIT:
                 return btrfs_ioctl_qgroup_limit(file, argp);
+        case BTRFS_IOC_QUOTA_RESCAN:
+                return btrfs_ioctl_quota_rescan(file, argp);
+        case BTRFS_IOC_QUOTA_RESCAN_STATUS:
+                return btrfs_ioctl_quota_rescan_status(file, argp);
         case BTRFS_IOC_DEV_REPLACE:
                 return btrfs_ioctl_dev_replace(root, argp);
         case BTRFS_IOC_GET_FSLABEL:
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 1fb7d8da3084..da8458357b57 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -31,13 +31,13 @@
 #include "locking.h"
 #include "ulist.h"
 #include "backref.h"
+#include "extent_io.h"
 
 /* TODO XXX FIXME
  *  - subvol delete -> delete when ref goes to 0? delete limits also?
  *  - reorganize keys
  *  - compressed
  *  - sync
- *  - rescan
  *  - copy also limits on subvol creation
  *  - limit
  *  - caches fuer ulists
@@ -98,6 +98,14 @@ struct btrfs_qgroup_list {
         struct btrfs_qgroup *member;
 };
 
+struct qgroup_rescan {
+        struct btrfs_work       work;
+        struct btrfs_fs_info    *fs_info;
+};
+
+static void qgroup_rescan_start(struct btrfs_fs_info *fs_info,
+                                struct qgroup_rescan *qscan);
+
 /* must be called with qgroup_ioctl_lock held */
 static struct btrfs_qgroup *find_qgroup_rb(struct btrfs_fs_info *fs_info,
                                            u64 qgroupid)
@@ -298,7 +306,20 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
                         }
                         fs_info->qgroup_flags = btrfs_qgroup_status_flags(l,
                                                                           ptr);
-                        /* FIXME read scan element */
+                        fs_info->qgroup_rescan_progress.objectid =
+                                        btrfs_qgroup_status_rescan(l, ptr);
+                        if (fs_info->qgroup_flags &
+                            BTRFS_QGROUP_STATUS_FLAG_RESCAN) {
+                                struct qgroup_rescan *qscan =
+                                        kmalloc(sizeof(*qscan), GFP_NOFS);
+                                if (!qscan) {
+                                        ret = -ENOMEM;
+                                        goto out;
+                                }
+                                fs_info->qgroup_rescan_progress.type = 0;
+                                fs_info->qgroup_rescan_progress.offset = 0;
+                                qgroup_rescan_start(fs_info, qscan);
+                        }
                         goto next1;
                 }
 
@@ -719,7 +740,8 @@ static int update_qgroup_status_item(struct btrfs_trans_handle *trans,
         ptr = btrfs_item_ptr(l, slot, struct btrfs_qgroup_status_item);
         btrfs_set_qgroup_status_flags(l, ptr, fs_info->qgroup_flags);
         btrfs_set_qgroup_status_generation(l, ptr, trans->transid);
-        /* XXX scan */
+        btrfs_set_qgroup_status_rescan(l, ptr,
+                                fs_info->qgroup_rescan_progress.objectid);
 
         btrfs_mark_buffer_dirty(l);
 
@@ -830,7 +852,7 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
         fs_info->qgroup_flags = BTRFS_QGROUP_STATUS_FLAG_ON |
                                 BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
         btrfs_set_qgroup_status_flags(leaf, ptr, fs_info->qgroup_flags);
-        btrfs_set_qgroup_status_scan(leaf, ptr, 0);
+        btrfs_set_qgroup_status_rescan(leaf, ptr, 0);
 
         btrfs_mark_buffer_dirty(leaf);
 
@@ -944,10 +966,11 @@ out:
         return ret;
 }
 
-int btrfs_quota_rescan(struct btrfs_fs_info *fs_info)
+static void qgroup_dirty(struct btrfs_fs_info *fs_info,
+                         struct btrfs_qgroup *qgroup)
 {
-        /* FIXME */
-        return 0;
+        if (list_empty(&qgroup->dirty))
+                list_add(&qgroup->dirty, &fs_info->dirty_qgroups);
 }
 
 int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans,
@@ -1155,13 +1178,6 @@ out:
         return ret;
 }
 
-static void qgroup_dirty(struct btrfs_fs_info *fs_info,
-                         struct btrfs_qgroup *qgroup)
-{
-        if (list_empty(&qgroup->dirty))
-                list_add(&qgroup->dirty, &fs_info->dirty_qgroups);
-}
-
 /*
  * btrfs_qgroup_record_ref is called when the ref is added or deleted. it puts
  * the modification into a list that's later used by btrfs_end_transaction to
@@ -1390,6 +1406,15 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
                 BUG();
         }
 
+        mutex_lock(&fs_info->qgroup_rescan_lock);
+        if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) {
+                if (fs_info->qgroup_rescan_progress.objectid <= node->bytenr) {
+                        mutex_unlock(&fs_info->qgroup_rescan_lock);
+                        return 0;
+                }
+        }
+        mutex_unlock(&fs_info->qgroup_rescan_lock);
+
         /*
          * the delayed ref sequence number we pass depends on the direction of
          * the operation. for add operations, we pass
@@ -1403,7 +1428,15 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
         if (ret < 0)
                 return ret;
 
+        mutex_lock(&fs_info->qgroup_rescan_lock);
         spin_lock(&fs_info->qgroup_lock);
+        if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) {
+                if (fs_info->qgroup_rescan_progress.objectid <= node->bytenr) {
+                        ret = 0;
+                        goto unlock;
+                }
+        }
+
         quota_root = fs_info->quota_root;
         if (!quota_root)
                 goto unlock;
@@ -1445,6 +1478,7 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
 
 unlock:
         spin_unlock(&fs_info->qgroup_lock);
+        mutex_unlock(&fs_info->qgroup_rescan_lock);
         ulist_free(roots);
         ulist_free(tmp);
 
@@ -1823,3 +1857,259 @@ void assert_qgroups_uptodate(struct btrfs_trans_handle *trans)
                 (u32)trans->delayed_ref_elem.seq);
         BUG();
 }
+
+/*
+ * returns < 0 on error, 0 when more leafs are to be scanned.
+ * returns 1 when done, 2 when done and FLAG_INCONSISTENT was cleared.
+ */
+static int
+qgroup_rescan_leaf(struct qgroup_rescan *qscan, struct btrfs_path *path,
+                   struct btrfs_trans_handle *trans, struct ulist *tmp,
+                   struct extent_buffer *scratch_leaf)
+{
+        struct btrfs_key found;
+        struct btrfs_fs_info *fs_info = qscan->fs_info;
+        struct ulist *roots = NULL;
+        struct ulist_node *unode;
+        struct ulist_iterator uiter;
+        struct seq_list tree_mod_seq_elem = {};
+        u64 seq;
+        int slot;
+        int ret;
+
+        path->leave_spinning = 1;
+        mutex_lock(&fs_info->qgroup_rescan_lock);
+        ret = btrfs_search_slot_for_read(fs_info->extent_root,
+                                         &fs_info->qgroup_rescan_progress,
+                                         path, 1, 0);
+
+        pr_debug("current progress key (%llu %u %llu), search_slot ret %d\n",
+                 (unsigned long long)fs_info->qgroup_rescan_progress.objectid,
+                 fs_info->qgroup_rescan_progress.type,
+                 (unsigned long long)fs_info->qgroup_rescan_progress.offset,
+                 ret);
+
+        if (ret) {
+                /*
+                 * The rescan is about to end, we will not be scanning any
+                 * further blocks. We cannot unset the RESCAN flag here, because
+                 * we want to commit the transaction if everything went well.
+                 * To make the live accounting work in this phase, we set our
+                 * scan progress pointer such that every real extent objectid
+                 * will be smaller.
+                 */
+                fs_info->qgroup_rescan_progress.objectid = (u64)-1;
+                btrfs_release_path(path);
+                mutex_unlock(&fs_info->qgroup_rescan_lock);
+                return ret;
+        }
+
+        btrfs_item_key_to_cpu(path->nodes[0], &found,
+                              btrfs_header_nritems(path->nodes[0]) - 1);
+        fs_info->qgroup_rescan_progress.objectid = found.objectid + 1;
+
+        btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem);
+        memcpy(scratch_leaf, path->nodes[0], sizeof(*scratch_leaf));
+        slot = path->slots[0];
+        btrfs_release_path(path);
+        mutex_unlock(&fs_info->qgroup_rescan_lock);
+
+        for (; slot < btrfs_header_nritems(scratch_leaf); ++slot) {
+                btrfs_item_key_to_cpu(scratch_leaf, &found, slot);
+                if (found.type != BTRFS_EXTENT_ITEM_KEY)
+                        continue;
+                ret = btrfs_find_all_roots(trans, fs_info, found.objectid,
+                                           tree_mod_seq_elem.seq, &roots);
+                if (ret < 0)
+                        goto out;
+                spin_lock(&fs_info->qgroup_lock);
+                seq = fs_info->qgroup_seq;
+                fs_info->qgroup_seq += roots->nnodes + 1; /* max refcnt */
+
+                ret = qgroup_account_ref_step1(fs_info, roots, tmp, seq);
+                if (ret) {
+                        spin_unlock(&fs_info->qgroup_lock);
+                        ulist_free(roots);
+                        goto out;
+                }
+
+                /*
+                 * step2 of btrfs_qgroup_account_ref works from a single root,
+                 * we're doing all at once here.
+                 */
+                ulist_reinit(tmp);
+                ULIST_ITER_INIT(&uiter);
+                while ((unode = ulist_next(roots, &uiter))) {
+                        struct btrfs_qgroup *qg;
+
+                        qg = find_qgroup_rb(fs_info, unode->val);
+                        if (!qg)
+                                continue;
+
+                        ret = ulist_add(tmp, qg->qgroupid, (uintptr_t)qg,
+                                        GFP_ATOMIC);
+                        if (ret < 0) {
+                                spin_unlock(&fs_info->qgroup_lock);
+                                ulist_free(roots);
+                                goto out;
+                        }
+                }
+
+                /* this loop is similar to step 2 of btrfs_qgroup_account_ref */
+                ULIST_ITER_INIT(&uiter);
+                while ((unode = ulist_next(tmp, &uiter))) {
+                        struct btrfs_qgroup *qg;
+                        struct btrfs_qgroup_list *glist;
+
+                        qg = (struct btrfs_qgroup *)(uintptr_t) unode->aux;
+                        qg->rfer += found.offset;
+                        qg->rfer_cmpr += found.offset;
+                        WARN_ON(qg->tag >= seq);
+                        if (qg->refcnt - seq == roots->nnodes) {
+                                qg->excl += found.offset;
+                                qg->excl_cmpr += found.offset;
+                        }
+                        qgroup_dirty(fs_info, qg);
+
+                        list_for_each_entry(glist, &qg->groups, next_group) {
+                                ret = ulist_add(tmp, glist->group->qgroupid,
+                                                (uintptr_t)glist->group,
+                                                GFP_ATOMIC);
+                                if (ret < 0) {
+                                        spin_unlock(&fs_info->qgroup_lock);
+                                        ulist_free(roots);
+                                        goto out;
+                                }
+                        }
+                }
+
+                spin_unlock(&fs_info->qgroup_lock);
+                ulist_free(roots);
+                ret = 0;
+        }
+
+out:
+        btrfs_put_tree_mod_seq(fs_info, &tree_mod_seq_elem);
+
+        return ret;
+}
+
+static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
+{
+        struct qgroup_rescan *qscan = container_of(work, struct qgroup_rescan,
+                                                   work);
+        struct btrfs_path *path;
+        struct btrfs_trans_handle *trans = NULL;
+        struct btrfs_fs_info *fs_info = qscan->fs_info;
+        struct ulist *tmp = NULL;
+        struct extent_buffer *scratch_leaf = NULL;
+        int err = -ENOMEM;
+
+        path = btrfs_alloc_path();
+        if (!path)
+                goto out;
+        tmp = ulist_alloc(GFP_NOFS);
+        if (!tmp)
+                goto out;
+        scratch_leaf = kmalloc(sizeof(*scratch_leaf), GFP_NOFS);
+        if (!scratch_leaf)
+                goto out;
+
+        err = 0;
+        while (!err) {
+                trans = btrfs_start_transaction(fs_info->fs_root, 0);
+                if (IS_ERR(trans)) {
+                        err = PTR_ERR(trans);
+                        break;
+                }
+                if (!fs_info->quota_enabled) {
+                        err = -EINTR;
+                } else {
+                        err = qgroup_rescan_leaf(qscan, path, trans,
+                                                 tmp, scratch_leaf);
+                }
+                if (err > 0)
+                        btrfs_commit_transaction(trans, fs_info->fs_root);
+                else
+                        btrfs_end_transaction(trans, fs_info->fs_root);
+        }
+
+out:
+        kfree(scratch_leaf);
+        ulist_free(tmp);
+        btrfs_free_path(path);
+        kfree(qscan);
+
+        mutex_lock(&fs_info->qgroup_rescan_lock);
+        fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;
+
+        if (err == 2 &&
+            fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT) {
+                fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
+        } else if (err < 0) {
+                fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
+        }
+        mutex_unlock(&fs_info->qgroup_rescan_lock);
+
+        if (err >= 0) {
+                pr_info("btrfs: qgroup scan completed%s\n",
+                        err == 2 ? " (inconsistency flag cleared)" : "");
+        } else {
+                pr_err("btrfs: qgroup scan failed with %d\n", err);
+        }
+}
+
+static void
+qgroup_rescan_start(struct btrfs_fs_info *fs_info, struct qgroup_rescan *qscan)
+{
+        memset(&qscan->work, 0, sizeof(qscan->work));
+        qscan->work.func = btrfs_qgroup_rescan_worker;
+        qscan->fs_info = fs_info;
+
+        pr_info("btrfs: qgroup scan started\n");
+        btrfs_queue_worker(&fs_info->qgroup_rescan_workers, &qscan->work);
+}
+
+int
+btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
+{
+        int ret = 0;
+        struct rb_node *n;
+        struct btrfs_qgroup *qgroup;
+        struct qgroup_rescan *qscan = kmalloc(sizeof(*qscan), GFP_NOFS);
+
+        if (!qscan)
+                return -ENOMEM;
+
+        mutex_lock(&fs_info->qgroup_rescan_lock);
+        spin_lock(&fs_info->qgroup_lock);
+        if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN)
+                ret = -EINPROGRESS;
+        else if (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON))
+                ret = -EINVAL;
+        if (ret) {
+                spin_unlock(&fs_info->qgroup_lock);
+                mutex_unlock(&fs_info->qgroup_rescan_lock);
+                kfree(qscan);
+                return ret;
+        }
+
+        fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_RESCAN;
+        memset(&fs_info->qgroup_rescan_progress, 0,
+                sizeof(fs_info->qgroup_rescan_progress));
+
+        /* clear all current qgroup tracking information */
+        for (n = rb_first(&fs_info->qgroup_tree); n; n = rb_next(n)) {
+                qgroup = rb_entry(n, struct btrfs_qgroup, node);
+                qgroup->rfer = 0;
+                qgroup->rfer_cmpr = 0;
+                qgroup->excl = 0;
+                qgroup->excl_cmpr = 0;
+        }
+        spin_unlock(&fs_info->qgroup_lock);
+        mutex_unlock(&fs_info->qgroup_rescan_lock);
+
+        qgroup_rescan_start(fs_info, qscan);
+
+        return 0;
+}
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 5e39e859a848..5ef0df545a2a 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -376,12 +376,18 @@ struct btrfs_ioctl_get_dev_stats {
 
 #define BTRFS_QUOTA_CTL_ENABLE  1
 #define BTRFS_QUOTA_CTL_DISABLE 2
-#define BTRFS_QUOTA_CTL_RESCAN  3
+#define BTRFS_QUOTA_CTL_RESCAN__NOTUSED 3
 struct btrfs_ioctl_quota_ctl_args {
         __u64 cmd;
         __u64 status;
 };
 
+struct btrfs_ioctl_quota_rescan_args {
+        __u64   flags;
+        __u64   progress;
+        __u64   reserved[6];
+};
+
 struct btrfs_ioctl_qgroup_assign_args {
         __u64 assign;
         __u64 src;
@@ -520,6 +526,10 @@ struct btrfs_ioctl_send_args {
                                struct btrfs_ioctl_qgroup_create_args)
 #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
                                struct btrfs_ioctl_qgroup_limit_args)
+#define BTRFS_IOC_QUOTA_RESCAN _IOW(BTRFS_IOCTL_MAGIC, 44, \
+                               struct btrfs_ioctl_quota_rescan_args)
+#define BTRFS_IOC_QUOTA_RESCAN_STATUS _IOR(BTRFS_IOCTL_MAGIC, 45, \
+                               struct btrfs_ioctl_quota_rescan_args)
 #define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
                                    char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_SET_FSLABEL _IOW(BTRFS_IOCTL_MAGIC, 50, \