Error when staging ostree sources when /tmp is mounted as a tmpfs on the host system - "Invalid cross-device link"

Summary

When staging OSTree sources, buildstream will attempt a rename between $XDG_CACHE_HOME/buildstream/sources/ostree and /tmp. If /tmp and $XDG_CACHE_HOME are not on the same block device (if /tmp is mounted as a tmpfs), this will fail.

Steps to reproduce

• Mount /tmp as a tmpfs ('systemctl enable tmp.mount && systemctl reboot' should work on most systems)
• Attempt to stage an OSTree source

What is the current bug behavior?

See summary

What is the expected correct behavior?

Staging of sources is not affected by host block device configuration.

Relevant logs and/or screenshots

Backtrace:

        An unhandled exception occured:          
                                                                                                                        
        Traceback (most recent call last):
          File "/usr/lib64/python3.6/shutil.py", line 544, in move                                     
            os.rename(src, real_dst)                                                                      
        OSError: [Errno 18] Invalid cross-device link: '/home/matthew/.cache/buildstream/sources/ostree/tmprk3jdzl0/checkout/usr' -> '/tmp/tmppqsog1z8/usr'
    
        During handling of the above exception, another exception occurred:
                
        Traceback (most recent call last):
          File "/usr/local/lib/python3.6/site-packages/buildstream/plugins/sources/ostree.py", line 160, in stage
            shutil.move(source_path, directory)
          File "/usr/lib64/python3.6/shutil.py", line 556, in move
            rmtree(src)
          File "/usr/lib64/python3.6/shutil.py", line 480, in rmtree
            _rmtree_safe_fd(fd, path, onerror)
          File "/usr/lib64/python3.6/shutil.py", line 418, in _rmtree_safe_fd
            _rmtree_safe_fd(dirfd, fullname, onerror)
          File "/usr/lib64/python3.6/shutil.py", line 438, in _rmtree_safe_fd
            onerror(os.unlink, fullname, sys.exc_info())          
          File "/usr/lib64/python3.6/shutil.py", line 436, in _rmtree_safe_fd
            os.unlink(name, dir_fd=topfd)
        PermissionError: [Errno 13] Permission denied: 'find'                         
                                                                                         
        The above exception was the direct cause of the following exception:
                
        Traceback (most recent call last):
          File "/usr/local/lib/python3.6/site-packages/buildstream/utils.py", line 986, in _tempdir
            yield tempdir                                                    
          File "/usr/local/lib/python3.6/site-packages/buildstream/source.py", line 624, in tempdir
            yield tempdir
          File "/usr/local/lib/python3.6/site-packages/buildstream/plugins/sources/ostree.py", line 163, in stage
            .format(self, self.url, tmpdir, directory, e)) from e
        buildstream.source.SourceError: ostree source at sdk.bst [line 4 column 2]: Failed to move ostree checkout http://d2dfs.uk.rdlabs.hpecorp.net/ostree/repo from '/home/matthew/.cache/buildstream/sources/ostree/tmprk3jdzl0' to '/tmp/tmppqsog1z8'
                                                                                     
        [Errno 13] Permission denied: 'find'                                              
                                                                                  
        During handling of the above exception, another exception occurred:                             
                                                                                               
        Traceback (most recent call last):
          File "/usr/local/lib/python3.6/site-packages/buildstream/element.py", line 1562, in _assemble
            collect = self.assemble(sandbox)                     
          File "/usr/local/lib/python3.6/site-packages/buildstream/plugins/elements/import.py", line 71, in assemble
            self._stage_sources_in_sandbox(sandbox, 'input', mount_workspaces=False)
          File "/usr/local/lib/python3.6/site-packages/buildstream/element.py", line 1364, in _stage_sources_in_sandbox
            self._stage_sources_at(host_vdirectory, mount_workspaces=mount_workspaces)
          File "/usr/local/lib/python3.6/site-packages/buildstream/element.py", line 1399, in _stage_sources_at
            source._stage(temp_staging_directory)                      
          File "/usr/local/lib/python3.6/site-packages/buildstream/source.py", line 680, in _stage
            self.stage(staging_directory)
          File "/usr/local/lib/python3.6/site-packages/buildstream/plugins/sources/ostree.py", line 163, in stage 
            .format(self, self.url, tmpdir, directory, e)) from e
          File "/usr/lib64/python3.6/contextlib.py", line 99, in __exit__                                               
            self.gen.throw(type, value, traceback)
          File "/usr/local/lib/python3.6/site-packages/buildstream/source.py", line 624, in tempdir                 
            yield tempdir         
          File "/usr/lib64/python3.6/contextlib.py", line 99, in __exit__                          
            self.gen.throw(type, value, traceback)                                                    
          File "/usr/local/lib/python3.6/site-packages/buildstream/utils.py", line 988, in _tempdir
            cleanup_tempdir()
          File "/usr/local/lib/python3.6/site-packages/buildstream/utils.py", line 982, in cleanup_tempdir
            shutil.rmtree(tempdir)
          File "/usr/lib64/python3.6/shutil.py", line 480, in rmtree
            _rmtree_safe_fd(fd, path, onerror)
          File "/usr/lib64/python3.6/shutil.py", line 418, in _rmtree_safe_fd
            _rmtree_safe_fd(dirfd, fullname, onerror)
          File "/usr/lib64/python3.6/shutil.py", line 418, in _rmtree_safe_fd
            _rmtree_safe_fd(dirfd, fullname, onerror)
          File "/usr/lib64/python3.6/shutil.py", line 418, in _rmtree_safe_fd
            _rmtree_safe_fd(dirfd, fullname, onerror)
          File "/usr/lib64/python3.6/shutil.py", line 438, in _rmtree_safe_fd
            onerror(os.unlink, fullname, sys.exc_info())
          File "/usr/lib64/python3.6/shutil.py", line 436, in _rmtree_safe_fd
            os.unlink(name, dir_fd=topfd)
        PermissionError: [Errno 13] Permission denied: 'find'
    
        During handling of the above exception, another exception occurred:
    
        Traceback (most recent call last):
          File "/usr/local/lib/python3.6/site-packages/buildstream/_scheduler/jobs/job.py", line 409, in _child_action
            result = self.child_process()                                   
          File "/usr/local/lib/python3.6/site-packages/buildstream/_scheduler/jobs/elementjob.py", line 94, in child_process
            return self._action_cb(self._element)
          File "/usr/local/lib/python3.6/site-packages/buildstream/_scheduler/queues/buildqueue.py", line 71, in process
            return element._assemble()    
          File "/usr/local/lib/python3.6/site-packages/buildstream/element.py", line 1640, in _assemble
            build_result_dict = {"success": self.__build_result[0], "description": self.__build_result[1]}
        TypeError: 'NoneType' object is not subscriptable

Possible fixes

Other relevant information

• BuildStream version affected: /milestone %BuildStream_v1.3
• commit 44da8175

---