Add test for backing up sparse files

2 files changed, 53 insertions, 0 deletions

diff --git a/yarns/0030-basics.yarn b/yarns/0030-basics.yarn
index 7cdc3ba7..0106eb0d 100644
--- a/yarns/0030-basics.yarn
+++ b/yarns/0030-basics.yarn
@@ -22,3 +22,28 @@ program must be able to handle.
     WHEN user backs up live data
     THEN user can restore their data correctly
     AND user can fsck the repository
+
+Backup sparse files
+-------------------
+
+Sparse files present an interesting challenge to backup programs. Most
+people have none, but some people have lots, and theirs can have very
+large holes. For example, at work I often generate disk images as
+raw disk images in sparse files. The image may need to be, say 30
+gigabytes in size, even though it only contains one or two gigabyte of
+data. The rest is a hole.
+
+A backup program should restore a sparse file as a sparse file.
+Otherwise, the 30 gigabyte disk image file will, upon restore, use 30
+gigabytes of disk space, rather than one. That might make restoring
+impossible.
+
+Unfortunately, it is not easy to (portably) check whether a file is
+sparse. We'll settle for making sure the restored file does not use
+more disk space than the one in live data.
+
+    SCENARIO backup a sparse file
+    GIVEN a file S in live data, with a hole, data, a hole
+    WHEN user backs up live data
+    THEN user can restore their data into X
+    AND restored file S in X doesn't use more disk
diff --git a/yarns/9000-implements.yarn b/yarns/9000-implements.yarn
index 41b6db4d..2cffdd69 100644
--- a/yarns/9000-implements.yarn
+++ b/yarns/9000-implements.yarn
@@ -34,6 +34,15 @@ for single-client scenarios.
     IMPLEMENTS GIVEN (\S+) of live data
     genbackupdata --quiet --create "$MATCH_1" "$LIVEDATA"
 
+We also need to generate a sparse file. A sparse file has at least one
+hole in it, and it may matter where the hole is: at the beginning,
+middle, or end of the file. Thus, we provide a way for scenarios to
+specify that.
+
+    IMPLEMENTS GIVEN a file (\S+) in live data, with (.+)
+    mkdir -p "$LIVEDATA"
+    "$SRCDIR/mksparse" "$LIVEDATA/$MATCH_1" "$MATCH_2"
+
 Backing up and verifying a backup
 ---------------------------------
 
@@ -59,3 +68,22 @@ We further verify that the repository itself is OK, by running
 
     IMPLEMENTS THEN user can fsck the repository
     run_obnam fsck -r "$REPO"
+
+Restoring data
+--------------
+
+We need a way to restore data from a test backup repository.
+
+    IMPLEMENTS THEN user can restore their data into (\S+)
+    run_obnam restore -r "$REPO" --to "$DATADIR/$MATCH_1"
+
+Checks on files
+---------------
+
+Check that a restored file uses at most as much disk space as the
+original one in live data.
+
+    IMPLEMENTS THEN restored file (\S+) in (\S+) doesn't use more disk
+    old=$(stat -c %b "$LIVEDATA/$MATCH_1")
+    new=$(stat -c %b "$DATADIR/$MATCH_2/$LIVEDATA/$MATCH_1")
+    test "$old" -lt "$new"