Stop moving staging areas of failed builds

Stop moving staging areas of failed builds from the 'staging' directory
to the 'failed' directory.  Moving staging areas make it very difficult
to debug build failures on the build essential chunks, as the paths set
on the configure scripts and some environment variables (e.g.
STAGE2_SYSROOT, DESTDIR) will be invalid after moving the staging area.

This change will also make it easier to create scripts that chroot n
environment similiar to the one where the build failure occurred.

To make it still possible to safely do a build an run `morph gc` in
parallel, we use flock(2) to control access to the staging area
directory.

Also, move the `test_supports_non_isolated_mode` test into a different
class, as it requires a different SetUp() routine (the staging area is
contructed with different parameters).

Change-Id: I06c3c435ad05c12afabc0adc2a9d4f8a284ccc02

1 files changed, 22 insertions, 20 deletions

diff --git a/morphlib/stagingarea.py b/morphlib/stagingarea.py
index 76bb3a18..c8c77229 100644
--- a/morphlib/stagingarea.py
+++ b/morphlib/stagingarea.py
@@ -20,6 +20,7 @@ import stat
 import cliapp
 from urlparse import urlparse
 import tempfile
+import fcntl
 
 import morphlib
 
@@ -58,6 +59,25 @@ class StagingArea(object):
             path = full_path + os.environ['PATH'].split(':')
         self.env['PATH'] = ':'.join(path)
 
+
+        # Keep trying until we have created a directory with an
+        # exclusive lock on it, as if the user runs `morph gc` in
+        # parallel the staging area directory could have been removed
+        # or have its exclusive lock associated with the `morph gc`
+        # process
+        while True:
+            try:
+                fd = os.open(dirname, os.O_RDONLY)
+                fcntl.flock(fd, fcntl.LOCK_EX)
+                if os.path.exists(dirname):
+                    self.staging_area_fd = fd
+                    break
+                else:
+                    os.close(fd) # pragma: no cover
+            except OSError: # pragma: no cover
+                if not os.path.exists(dirname):
+                    os.makedirs(dirname)
+
     # Wrapper to be overridden by unit tests.
     def _mkdir(self, dirname):  # pragma: no cover
         os.makedirs(dirname)
@@ -170,9 +190,6 @@ class StagingArea(object):
             #       the other renamed its tempdir here first.
             os.rename(savedir, unpacked_artifact)
 
-        if not os.path.exists(self.dirname):
-            self._mkdir(self.dirname)
-
         self.hardlink_all_files(unpacked_artifact, self.dirname)
 
     def remove(self):
@@ -185,6 +202,7 @@ class StagingArea(object):
         '''
 
         shutil.rmtree(self.dirname)
+        os.close(self.staging_area_fd)
 
     to_mount_in_staging = (
         ('dev/shm', 'tmpfs', 'none'),
@@ -303,21 +321,5 @@ class StagingArea(object):
             msg = morphlib.util.error_message_for_containerised_commandline(
                 argv, err, container_config)
             raise cliapp.AppException(
-                'In staging area %s: %s' % (self._failed_location(), msg))
-
-    def _failed_location(self):  # pragma: no cover
-        '''Path this staging area will be moved to if an error occurs.'''
-        return os.path.join(self._app.settings['tempdir'], 'failed',
-                            os.path.basename(self.dirname))
-
-    def abort(self): # pragma: no cover
-        '''Handle what to do with a staging area in the case of failure.
-           This may either remove it or save it for later inspection.
-        '''
-        # TODO: when we add the option to throw away failed builds,
-        #       hook it up here
-
-        dest_dir = self._failed_location()
-        os.rename(self.dirname, dest_dir)
-        self.dirname = dest_dir
+                'In staging area %s: %s' % (self.dirname, msg))