Don't skip parts of a file when calling fiemap

A mis-incremented offset in the fiemap-processing code meant that
non-sparse portions of files were missed.

src/client.c

@@ -140,8 +140,11 @@ void write_not_zeroes(struct client* client, uint64_t from, int len)
 				 * and memcpy being fast, rather than try to
 				 * hand-optimized something specific.
 				 */
-				if (zerobuffer[0] != 0 ||
+
-				    memcmp(zerobuffer, zerobuffer + 1, blockrun - 1)) {
+				int all_zeros = (zerobuffer[0] == 0) && 
+					(0 == memcmp( zerobuffer, zerobuffer+1, blockrun-1 ));
+
+				if ( !all_zeros ) {
 					memcpy(client->mapped+from, zerobuffer, blockrun);
 					bitset_set_range(map, from, blockrun);
 					server_dirty(client->serve, from, blockrun);

src/ioutil.c

@@ -64,7 +64,7 @@ int build_allocation_map(struct bitset_mapping* allocation_map, int fd)
 				struct fiemap_extent *last = &fiemap->fm_extents[
 					fiemap->fm_mapped_extents-1
 				];
-				offset += last->fe_logical + last->fe_length;
+				offset = last->fe_logical + last->fe_length;
 			}
 			else {
 				offset += fiemap->fm_length;

tests/acceptance/environment.rb

@@ -78,6 +78,10 @@ class Environment
   end
 
 
+  def write1( data )
+    @nbd1.write( 0, data )
+  end
+
   def writefile1(data)
     @file1 = FileWriter.new(@filename1, @blocksize).write(data)
   end

tests/acceptance/test_happy_path.rb

@@ -129,5 +129,32 @@ class TestHappyPath < Test::Unit::TestCase
     assert_no_match( /^(F|E):/, stderr )
   end
 
+
+  def test_write_more_than_one_run
+    one_mb = 2**20
+    data = "\0" * 256 * one_mb
+
+    File.open(@env.filename1, "wb") do |f| f.write( "1" * 256 * one_mb ) end
+
+    @env.serve1
+    sleep 5
+    @env.write1( data )
+    @env.nbd1.can_die(0)
+    @env.nbd1.kill
+
+    i = 0
+    File.open(@env.filename1, "rb") do |f|
+      while mb = f.read( one_mb )
+        unless "\0"*one_mb == mb
+          msg = "Read non-zeros after offset %x:\n"%(i * one_mb)
+          msg += `hexdump #{@env.filename1} | head -n5`
+          fail msg
+        end
+        i += 1
+      end
+    end
+    p i
+  end
+
 end