[PATCH v2 1/3] btrfs: introduce BTRFS_EXCLOP_BALANCE_PAUSED exclusive state

[Nikolay Borisov <nborisov@suse.com>]

Current set of exclusive operation states is not sufficient to handle all
practical use cases. In particular there is a need to be able to add a
device to a filesystem that have paused balance. Currently there is no
way to distinguish between a running and a paused balance. Fix this by
introducing BTRFS_EXCLOP_BALANCE_PAUSED which is going to be set in 2
occasions:

1. When a filesystem is mounted with skip_balance and there is an
   unfinished balance it will now be into BALANCE_PAUSED instead of
   simply BALANCE state.

2. When a running balance is paused.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/ctree.h   |  3 +++
 fs/btrfs/ioctl.c   | 13 +++++++++++++
 fs/btrfs/volumes.c | 11 +++++++++--
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 7553e9dc5f93..8376271bfed1 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -613,6 +613,7 @@ enum {
  */
 enum btrfs_exclusive_operation {
 	BTRFS_EXCLOP_NONE,
+	BTRFS_EXCLOP_BALANCE_PAUSED,
 	BTRFS_EXCLOP_BALANCE,
 	BTRFS_EXCLOP_DEV_ADD,
 	BTRFS_EXCLOP_DEV_REMOVE,
@@ -3305,6 +3306,8 @@ bool btrfs_exclop_start_try_lock(struct btrfs_fs_info *fs_info,
 				 enum btrfs_exclusive_operation type);
 void btrfs_exclop_start_unlock(struct btrfs_fs_info *fs_info);
 void btrfs_exclop_finish(struct btrfs_fs_info *fs_info);
+void btrfs_exclop_pause_balance(struct btrfs_fs_info *fs_info);
+
 
 /* file.c */
 int __init btrfs_auto_defrag_init(void);
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 92424a22d8d6..f4c05a9aab84 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -414,6 +414,15 @@ void btrfs_exclop_finish(struct btrfs_fs_info *fs_info)
 	sysfs_notify(&fs_info->fs_devices->fsid_kobj, NULL, "exclusive_operation");
 }
 
+void btrfs_exclop_pause_balance(struct btrfs_fs_info *fs_info)
+{
+	spin_lock(&fs_info->super_lock);
+	ASSERT(fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE ||
+	       fs_info->exclusive_operation == BTRFS_EXCLOP_DEV_ADD);
+	fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE_PAUSED;
+	spin_unlock(&fs_info->super_lock);
+}
+
 static int btrfs_ioctl_getversion(struct file *file, int __user *arg)
 {
 	struct inode *inode = file_inode(file);
@@ -4020,6 +4029,10 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 			if (fs_info->balance_ctl &&
 			    !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
 				/* this is (3) */
+				spin_lock(&fs_info->super_lock);
+				ASSERT(fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE_PAUSED);
+				fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE;
+				spin_unlock(&fs_info->super_lock);
 				need_unlock = false;
 				goto locked;
 			}
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index cc80f2a97a0b..e87f9ac440c2 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4355,8 +4355,10 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
 	ret = __btrfs_balance(fs_info);
 
 	mutex_lock(&fs_info->balance_mutex);
-	if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req))
+	if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) {
 		btrfs_info(fs_info, "balance: paused");
+		btrfs_exclop_pause_balance(fs_info);
+	}
 	/*
 	 * Balance can be canceled by:
 	 *
@@ -4406,6 +4408,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
 static int balance_kthread(void *data)
 {
 	struct btrfs_fs_info *fs_info = data;
+	bool paused = false;
 	int ret = 0;
 
 	mutex_lock(&fs_info->balance_mutex);
@@ -4432,6 +4435,10 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
 		return 0;
 	}
 
+	spin_lock(&fs_info->super_lock);
+	ASSERT(fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE_PAUSED);
+	fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE;
+	spin_unlock(&fs_info->super_lock);
 	/*
 	 * A ro->rw remount sequence should continue with the paused balance
 	 * regardless of who pauses it, system or the user as of now, so set
@@ -4500,7 +4507,7 @@ int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
 	 * is in a paused state and must have fs_info::balance_ctl properly
 	 * set up.
 	 */
-	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE))
+	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE_PAUSED))
 		btrfs_warn(fs_info,
 	"balance: cannot set exclusive op status, resume manually");
 
-- 
2.25.1