Use Kernel::exec instead of system()

We don't need to keep the ruby process around once we've
established that it's ok to run a git command.

lib/gitlab_shell.rb

@@ -44,13 +44,17 @@ class GitlabShell
 
   def process_cmd
     repo_full_path = File.join(repos_path, repo_name)
-    system("#{@git_cmd} #{repo_full_path}")
+    exec_cmd "#{@git_cmd} #{repo_full_path}"
   end
 
   def validate_access
     api.allowed?(@git_cmd, @repo_name, @key_id, '_any')
   end
 
+  def exec_cmd args
+    Kernel::exec args
+  end
+
   def api
     GitlabNet.new
   end

spec/gitlab_shell_spec.rb

@@ -5,7 +5,7 @@ describe GitlabShell do
   subject do
     ARGV[0] = 'key-56'
     GitlabShell.new.tap do |shell|
-      shell.stub(process_cmd: true)
+      shell.stub(exec_cmd: :exec_called)
       shell.stub(api: api)
     end
   end
@@ -53,6 +53,10 @@ describe GitlabShell do
       it "should process the command" do
         subject.should_receive(:process_cmd).with()
       end
+
+      it "should execute the command" do
+        subject.should_receive(:exec_cmd).with("git-upload-pack /home/git/repositories/gitlab-ci.git")
+      end
     end
 
     context 'git-receive-pack' do
@@ -62,6 +66,10 @@ describe GitlabShell do
       it "should process the command" do
         subject.should_receive(:process_cmd).with()
       end
+
+      it "should execute the command" do
+        subject.should_receive(:exec_cmd).with("git-receive-pack /home/git/repositories/gitlab-ci.git")
+      end
     end
 
     context 'arbitrary command' do
@@ -71,6 +79,10 @@ describe GitlabShell do
       it "should not process the command" do
         subject.should_not_receive(:process_cmd)
       end
+
+      it "should not execute the command" do
+        subject.should_not_receive(:exec_cmd)
+      end
     end
 
     context 'no command' do