Btrfs: allow for resuming restriper after it was paused

Recognize BTRFS_BALANCE_RESUME flag passed from userspace.  We use the
same heuristics used when recovering balance after a crash to try to
start where we left off last time.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 60852217ce9a..85e546ffe3c7 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3106,6 +3106,20 @@ static long btrfs_ioctl_balance(struct btrfs_root *root, void __user *arg)
                         ret = PTR_ERR(bargs);
                         goto out;
                 }
+
+                if (bargs->flags & BTRFS_BALANCE_RESUME) {
+                        if (!fs_info->balance_ctl) {
+                                ret = -ENOTCONN;
+                                goto out_bargs;
+                        }
+
+                        bctl = fs_info->balance_ctl;
+                        spin_lock(&fs_info->balance_lock);
+                        bctl->flags |= BTRFS_BALANCE_RESUME;
+                        spin_unlock(&fs_info->balance_lock);
+
+                        goto do_balance;
+                }
         } else {
                 bargs = NULL;
         }
@@ -3133,6 +3147,7 @@ static long btrfs_ioctl_balance(struct btrfs_root *root, void __user *arg)
                 bctl->flags |= BTRFS_BALANCE_TYPE_MASK;
         }
 
+do_balance:
         ret = btrfs_balance(bctl, bargs);
         /*
          * bctl is freed in __cancel_balance or in free_fs_info if