Btrfs: changes to live filesystem are also written to replacement disk

During a running dev replace operation, all write requests to
the live filesystem are duplicated to also write to the target
drive. Therefore btrfs_map_block() is changed to duplicate
stripes that are written to the source disk of a device replace
procedure to be written to the target disk as well.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 49 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index de0c05cca390..4d3bf187ab52 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4044,6 +4044,9 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw,
         int num_stripes;
         int max_errors = 0;
         struct btrfs_bio *bbio = NULL;
+        struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
+        int dev_replace_is_ongoing = 0;
+        int num_alloc_stripes;
 
         read_lock(&em_tree->lock);
         em = lookup_extent_mapping(em_tree, logical, *length);
@@ -4089,6 +4092,11 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw,
         if (!bbio_ret)
                 goto out;
 
+        btrfs_dev_replace_lock(dev_replace);
+        dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(dev_replace);
+        if (!dev_replace_is_ongoing)
+                btrfs_dev_replace_unlock(dev_replace);
+
         num_stripes = 1;
         stripe_index = 0;
         stripe_nr_orig = stripe_nr;
@@ -4155,7 +4163,10 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw,
         }
         BUG_ON(stripe_index >= map->num_stripes);
 
-        bbio = kzalloc(btrfs_bio_size(num_stripes), GFP_NOFS);
+        num_alloc_stripes = num_stripes;
+        if (dev_replace_is_ongoing && (rw & (REQ_WRITE | REQ_DISCARD)))
+                num_alloc_stripes <<= 1;
+        bbio = kzalloc(btrfs_bio_size(num_alloc_stripes), GFP_NOFS);
         if (!bbio) {
                 ret = -ENOMEM;
                 goto out;
@@ -4250,11 +4261,48 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw,
                 }
         }
 
+        if (dev_replace_is_ongoing && (rw & (REQ_WRITE | REQ_DISCARD)) &&
+            dev_replace->tgtdev != NULL) {
+                int index_where_to_add;
+                u64 srcdev_devid = dev_replace->srcdev->devid;
+
+                /*
+                 * duplicate the write operations while the dev replace
+                 * procedure is running. Since the copying of the old disk
+                 * to the new disk takes place at run time while the
+                 * filesystem is mounted writable, the regular write
+                 * operations to the old disk have to be duplicated to go
+                 * to the new disk as well.
+                 * Note that device->missing is handled by the caller, and
+                 * that the write to the old disk is already set up in the
+                 * stripes array.
+                 */
+                index_where_to_add = num_stripes;
+                for (i = 0; i < num_stripes; i++) {
+                        if (bbio->stripes[i].dev->devid == srcdev_devid) {
+                                /* write to new disk, too */
+                                struct btrfs_bio_stripe *new =
+                                        bbio->stripes + index_where_to_add;
+                                struct btrfs_bio_stripe *old =
+                                        bbio->stripes + i;
+
+                                new->physical = old->physical;
+                                new->length = old->length;
+                                new->dev = dev_replace->tgtdev;
+                                index_where_to_add++;
+                                max_errors++;
+                        }
+                }
+                num_stripes = index_where_to_add;
+        }
+
         *bbio_ret = bbio;
         bbio->num_stripes = num_stripes;
         bbio->max_errors = max_errors;
         bbio->mirror_num = mirror_num;
 out:
+        if (dev_replace_is_ongoing)
+                btrfs_dev_replace_unlock(dev_replace);
         free_extent_map(em);
         return ret;
 }