Btrfs: fix send to deal with sparse files properly

Send was just sending everything it found, even if the extent was a hole.  This
is unpleasant for users, so just skip holes when we are sending.  This will also
skip sending prealloc extents since the send spec doesn't have a prealloc
command.  Eventually we will add a prealloc command and rev the send version so
we can send down the prealloc info.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 31 insertions, 3 deletions

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index db7da682f0d2..cbe92da5f33b 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -3920,7 +3920,8 @@ static int is_extent_unchanged(struct send_ctx *sctx,
         btrfs_item_key_to_cpu(eb, &found_key, slot);
         if (found_key.objectid != key.objectid ||
             found_key.type != key.type) {
-                ret = 0;
+                /* If we're a hole then just pretend nothing changed */
+                ret = (left_disknr) ? 0 : 1;
                 goto out;
         }
 
@@ -3946,7 +3947,8 @@ static int is_extent_unchanged(struct send_ctx *sctx,
                  * This may only happen on the first iteration.
                  */
                 if (found_key.offset + right_len <= ekey->offset) {
-                        ret = 0;
+                        /* If we're a hole just pretend nothing changed */
+                        ret = (left_disknr) ? 0 : 1;
                         goto out;
                 }
 
@@ -4011,8 +4013,8 @@ static int process_extent(struct send_ctx *sctx,
                           struct btrfs_path *path,
                           struct btrfs_key *key)
 {
-        int ret = 0;
         struct clone_root *found_clone = NULL;
+        int ret = 0;
 
         if (S_ISLNK(sctx->cur_inode_mode))
                 return 0;
@@ -4025,6 +4027,32 @@ static int process_extent(struct send_ctx *sctx,
                         ret = 0;
                         goto out;
                 }
+        } else {
+                struct btrfs_file_extent_item *ei;
+                u8 type;
+
+                ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
+                                    struct btrfs_file_extent_item);
+                type = btrfs_file_extent_type(path->nodes[0], ei);
+                if (type == BTRFS_FILE_EXTENT_PREALLOC ||
+                    type == BTRFS_FILE_EXTENT_REG) {
+                        /*
+                         * The send spec does not have a prealloc command yet,
+                         * so just leave a hole for prealloc'ed extents until
+                         * we have enough commands queued up to justify rev'ing
+                         * the send spec.
+                         */
+                        if (type == BTRFS_FILE_EXTENT_PREALLOC) {
+                                ret = 0;
+                                goto out;
+                        }
+
+                        /* Have a hole, just skip it. */
+                        if (btrfs_file_extent_disk_bytenr(path->nodes[0], ei) == 0) {
+                                ret = 0;
+                                goto out;
+                        }
+                }
         }
 
         ret = find_extent_clone(sctx, path, key->objectid, key->offset,