Hardlinked chroot done with linux-user-chroot

The patch gives two things.

Improves morph build time by reusing decompressed files of
chunks/stage-fillers with hardlinks from the chroot. Rather than
decompressing each time into each chroot.

Original: real    5h 17m 47s
Hardlink: real    2h 52m 27s

It uses linux-user-chroot to create the chroot and make all but
the basics readonly.

2 files changed, 64 insertions, 34 deletions

diff --git a/morphlib/builder2.py b/morphlib/builder2.py
index c7d25e1a..402c17f4 100644
--- a/morphlib/builder2.py
+++ b/morphlib/builder2.py
@@ -259,53 +259,30 @@ class ChunkBuilder(BuilderBase):
 
     def build_and_cache(self):  # pragma: no cover
         with self.build_watch('overall-build'):
-            mounted = self.do_mounts()
+            
+            builddir, destdir = self.staging_area.chroot_open(self.artifact.source)
             log_name = None
             try:
-                builddir = self.staging_area.builddir(self.artifact.source)
                 self.get_sources(builddir)
-                destdir = self.staging_area.destdir(self.artifact.source)
                 with self.local_artifact_cache.put_source_metadata(
                         self.artifact.source, self.artifact.cache_key,
                         'build-log') as log:
                     log_name = log.real_filename
                     self.run_commands(builddir, destdir, log)
             except:
-                self.do_unmounts(mounted)
+                self.staging_area.chroot_close()
                 if log_name:
                     with open(log_name) as f:
                         for line in f:
                             logging.error('OUTPUT FROM FAILED BUILD: %s' %
                                           line.rstrip('\n'))
                 raise
-            self.do_unmounts(mounted)
+            self.staging_area.chroot_close()
             built_artifacts = self.assemble_chunk_artifacts(destdir)
 
         self.save_build_times()
         return built_artifacts
 
-    to_mount = (
-        ('proc',    'proc',  'none'),
-        ('dev/shm', 'tmpfs', 'none'),
-    )
-
-    def do_mounts(self):  # pragma: no cover
-        mounted = []
-        if not self.setup_mounts:
-            return mounted
-        for mount_point, mount_type, source in ChunkBuilder.to_mount:
-            logging.debug('Mounting %s in staging area' % mount_point)
-            path = os.path.join(self.staging_area.dirname, mount_point)
-            if not os.path.exists(path):
-                os.makedirs(path)
-            self.app.runcmd(['mount', '-t', mount_type, source, path])
-            mounted.append(path)
-        return mounted
-
-    def do_unmounts(self, mounted):  # pragma: no cover
-        for path in mounted:
-            logging.debug('Unmounting %s in staging area' % path)
-            morphlib.fsutils.unmount(self.app.runcmd, path)
 
     def get_sources(self, srcdir):  # pragma: no cover
         '''Get sources from git to a source directory, for building.'''
@@ -392,10 +369,12 @@ class ChunkBuilder(BuilderBase):
                         # buffers, but flush handles both
                         logfile.write('# # %s\n' % cmd)
                         logfile.flush()
-                        self.runcmd(['sh', '-c', cmd],
-                                    cwd=relative_builddir,
-                                    stdout=logfile,
-                                    stderr=subprocess.STDOUT)
+
+                        self.staging_area.runcmd(['sh', '-c', cmd],
+                                                cwd=relative_builddir,
+                                                stdout=logfile,
+                                                stderr=subprocess.STDOUT)
+
                         logfile.flush()
                     except cliapp.AppException, e:
                         logfile.flush()
diff --git a/morphlib/stagingarea.py b/morphlib/stagingarea.py
index a87b45c3..31fb8410 100644
--- a/morphlib/stagingarea.py
+++ b/morphlib/stagingarea.py
@@ -40,6 +40,8 @@ class StagingArea(object):
         self._app = app
         self.dirname = dirname
         self.tempdir = tempdir
+        self.builddirname = None
+        self.destdirname = None        
 
     # Wrapper to be overridden by unit tests.
     def _mkdir(self, dirname):  # pragma: no cover
@@ -90,7 +92,17 @@ class StagingArea(object):
 
         logging.debug('Installing artifact %s' %
                       getattr(handle, 'name', 'unknown name'))
-        morphlib.bins.unpack_binary_from_file(handle, self.dirname)
+
+        decompressed_artifact = os.path.join(self._app.settings['cachedir'],'artifacts',os.path.basename(handle.name) + '.d')
+        if not os.path.exists(decompressed_artifact):
+            self._mkdir(decompressed_artifact)
+            morphlib.bins.unpack_binary_from_file(handle, decompressed_artifact + "/")
+            
+        if not os.path.exists(self.dirname):
+            self._mkdir(self.dirname)
+
+        self._app.runcmd(["cp -al " + decompressed_artifact+"/* " + self.dirname+"/"],shell=True)
+
 
     def remove(self):
         '''Remove the entire staging area.
@@ -103,6 +115,27 @@ class StagingArea(object):
 
         shutil.rmtree(self.dirname)
 
+    def chroot_open(self, source):
+        # After setup, and before it's use as a chroot
+
+        assert self.builddirname == None and self.destdirname == None
+
+        builddir = self.builddir(source)
+        destdir = self.destdir(source)
+        self.builddirname = self.relative(builddir).lstrip('/')
+        self.destdirname = self.relative(destdir).lstrip('/')
+
+        for mount_point in ['proc','dev/shm']:
+            path = os.path.join(self.dirname, mount_point)
+            if not os.path.exists(path):
+                os.makedirs(path)
+
+        return builddir, destdir
+
+    def chroot_close(self):
+        # After it's use as a chroot is complete.
+        pass
+
     def runcmd(self, argv, **kwargs):  # pragma: no cover
         '''Run a command in a chroot in the staging area.'''
         cwd = kwargs.get('cwd') or '/'
@@ -111,6 +144,24 @@ class StagingArea(object):
             del kwargs['cwd']
         else:
             cwd = '/'
-        real_argv = ['chroot', self.dirname, 'sh', '-c',
-                     'cd "$1" && shift && exec "$@"', '--', cwd] + argv
+
+        entries = os.listdir(self.dirname)
+    
+        for friend in [self.builddirname,self.destdirname,'dev','proc','tmp']:
+            try:
+                entries.remove(friend)
+            except:
+                pass
+
+        real_argv = ['linux-user-chroot']
+
+        for entry in entries:
+            real_argv += ['--mount-readonly',"/"+entry]
+            
+        real_argv += ['--mount-proc','/proc']
+        real_argv += ['--mount-bind','/dev/shm','/dev/shm']
+        real_argv += [self.dirname, 'sh', '-c',
+                     'cd "$1" && shift && exec "$@"', '--', cwd]
+        real_argv += argv
+
         return self._app.runcmd(real_argv, **kwargs)