[PATCH 10/13] btrfs: introduce helper functions to perform hot replace

[Anand Jain <anand.jain@oracle.com>]

Hot replace / auto replace is important volume manager feature
and is critical to the data center operations, so that the degraded
volume can be brought back to a healthy state at the earliest and
without manual intervention.

This modifies the existing replace code to suite the need of auto
replace, in the long run I hope both the codes to be merged.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Tested-by: Austin S. Hemmelgarn <ahferroin7@gmail.com>
---
 fs/btrfs/dev-replace.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/dev-replace.h |  1 +
 2 files changed, 44 insertions(+)

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 2b926867d136..ceab4c51db32 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -957,3 +957,46 @@ void btrfs_bio_counter_inc_blocked(struct btrfs_fs_info *fs_info)
 				     &fs_info->fs_state));
 	}
 }
+
+int btrfs_auto_replace_start(struct btrfs_root *root,
+				struct btrfs_device *src_device)
+{
+	int ret;
+	char *tgt_path;
+	char *src_path;
+	struct btrfs_fs_info *fs_info = root->fs_info;
+
+	if (fs_info->sb->s_flags & MS_RDONLY)
+		return -EROFS;
+
+	btrfs_dev_replace_lock(&fs_info->dev_replace, 0);
+	if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
+		btrfs_dev_replace_unlock(&fs_info->dev_replace, 0);
+		return -EBUSY;
+	}
+	btrfs_dev_replace_unlock(&fs_info->dev_replace, 0);
+
+	if (btrfs_get_spare_device(&tgt_path)) {
+		btrfs_err(root->fs_info,
+			"No spare device found/configured in the kernel");
+		return -EINVAL;
+	}
+
+	rcu_read_lock();
+	src_path = kstrdup(rcu_str_deref(src_device->name), GFP_ATOMIC);
+	rcu_read_unlock();
+	if (!src_path) {
+		kfree(tgt_path);
+		return -ENOMEM;
+	}
+	ret = btrfs_dev_replace_start(root, tgt_path,
+					src_device->devid, src_path,
+		BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_AVOID);
+	if (ret)
+		btrfs_put_spare_device(tgt_path);
+
+	kfree(tgt_path);
+	kfree(src_path);
+
+	return 0;
+}
diff --git a/fs/btrfs/dev-replace.h b/fs/btrfs/dev-replace.h
index e922b42d91df..b918b9d6e5df 100644
--- a/fs/btrfs/dev-replace.h
+++ b/fs/btrfs/dev-replace.h
@@ -46,4 +46,5 @@ static inline void btrfs_dev_replace_stats_inc(atomic64_t *stat_value)
 {
 	atomic64_inc(stat_value);
 }
+int btrfs_auto_replace_start(struct btrfs_root *root, struct btrfs_device *src_device);
 #endif
-- 
2.7.0