bst shell: Added --isolate option, disabled by default.tristan/isolate-shell

This changes a few things:

  o How the shell environment and sandbox modes are setup is
    not decided by whether a `--build` sandbox was staged or not

  o In interactive build debugging mode, an isolated build
    sandbox is used

  o The bst shell command now has the option to control it

  o All invocations of bst shell now use a read-only rootfs,
    avoiding FUSE layer and file descriptor limits (this can
    be made optional later if needed)

This is a part of issue #223

3 files changed, 19 insertions, 17 deletions

diff --git a/buildstream/_frontend/cli.py b/buildstream/_frontend/cli.py
index 9d203427f..c5fc87bab 100644
--- a/buildstream/_frontend/cli.py
+++ b/buildstream/_frontend/cli.py
@@ -458,20 +458,22 @@ def show(app, elements, deps, except_, order, format, downloadable):
 ##################################################################
 @cli.command(short_help="Shell into an element's sandbox environment")
 @click.option('--build', '-b', is_flag=True, default=False,
-              help='Create a build sandbox')
+              help='Stage dependencies and sources to build')
 @click.option('--sysroot', '-s', default=None,
               type=click.Path(exists=True, file_okay=False, readable=True),
               help="An existing sysroot")
+@click.option('--isolate', is_flag=True, default=False,
+              help='Create an isolated build sandbox')
 @click.argument('element',
                 type=click.Path(dir_okay=False, readable=True))
 @click.argument('command', type=click.STRING, nargs=-1)
 @click.pass_obj
-def shell(app, element, sysroot, build, command):
+def shell(app, element, sysroot, isolate, build, command):
     """Run a command in the target element's sandbox environment
 
-    This will first stage a temporary sysroot for running
-    the target element, assuming it has already been built
-    and all required artifacts are in the local cache.
+    This will stage a temporary sysroot for running the target
+    element, assuming it has already been built and all required
+    artifacts are in the local cache.
 
     Use the --build option to create a temporary sysroot for
     building the element instead.
@@ -508,7 +510,7 @@ def shell(app, element, sysroot, build, command):
         sys.exit(-1)
 
     try:
-        exitcode = app.pipeline.targets[0]._shell(scope, sysroot, command=command)
+        exitcode = app.pipeline.targets[0]._shell(scope, sysroot, isolate=isolate, command=command)
         sys.exit(exitcode)
     except BstError as e:
         click.echo("", err=True)
diff --git a/buildstream/_frontend/main.py b/buildstream/_frontend/main.py
index 9cab22c4a..dc251748d 100644
--- a/buildstream/_frontend/main.py
+++ b/buildstream/_frontend/main.py
@@ -342,7 +342,7 @@ class App():
                 if choice == 'shell':
                     click.echo("\nDropping into an interactive shell in the failed build sandbox\n", err=True)
                     try:
-                        element._shell(Scope.BUILD, failure.sandbox)
+                        element._shell(Scope.BUILD, failure.sandbox, isolate=True)
                     except BstError as e:
                         click.echo("Error while attempting to create interactive shell: {}".format(e), err=True)
                 elif choice == 'log':
diff --git a/buildstream/element.py b/buildstream/element.py
index c43701d09..f0df03b26 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -1368,18 +1368,25 @@ class Element(Plugin):
     # Args:
     #    scope (Scope): Either BUILD or RUN scopes are valid, or None
     #    directory (str): A directory to an existing sandbox, or None
+    #    isolate (bool): Whether to isolate the environment like we do in builds
     #    command (list): An argv to launch in the sandbox
     #
     # Returns: Exit code
     #
     # If directory is not specified, one will be staged using scope
-    def _shell(self, scope=None, directory=None, command=None):
+    def _shell(self, scope=None, directory=None, isolate=False, command=None):
 
         with self._prepare_sandbox(scope, directory) as sandbox:
             environment = self.get_environment()
-            flags = SandboxFlags.INTERACTIVE
+            flags = SandboxFlags.INTERACTIVE | SandboxFlags.ROOT_READ_ONLY
+
+            # Special configurations for non-isolated sandboxes
+            if not isolate:
+
+                # Open the network, and reuse calling uid/gid
+                #
+                flags |= SandboxFlags.NETWORK_ENABLED | SandboxFlags.INHERIT_UID
 
-            if scope == Scope.RUN:
                 # If a testing sandbox was requested, override the element environment
                 # with some of the host environment and use that for the shell.
                 #
@@ -1390,13 +1397,6 @@ class Element(Plugin):
                     if os.environ.get(override) is not None:
                         environment[override] = os.environ.get(override)
 
-            # Decide whether to create a build style sandbox or an open
-            # testing sandbox based on whether the build scope was requested
-            if scope == Scope.BUILD:
-                flags |= SandboxFlags.ROOT_READ_ONLY
-            elif scope == Scope.RUN:
-                flags |= SandboxFlags.NETWORK_ENABLED | SandboxFlags.INHERIT_UID
-
             if command:
                 argv = [arg for arg in command]
             else: