catalyst: Add and use namespace context manager

Wraps snakeoil's simple_unshare; returns to the previous namespaces on
context exit. Will be used by the next commit.

Signed-off-by: Matt Turner <mattst88@gentoo.org>

2 files changed, 39 insertions, 10 deletions

diff --git a/catalyst/context.py b/catalyst/context.py
new file mode 100644
index 00000000..8a58f33d
--- /dev/null
+++ b/catalyst/context.py
@@ -0,0 +1,32 @@
+
+import contextlib
+import os
+
+from snakeoil.process.namespaces import setns, simple_unshare
+
+@contextlib.contextmanager
+def namespace(mount=False, uts=False, ipc=False, net=False, pid=False,
+              user=False, hostname=None):
+    namespaces = {
+        (mount, "mnt"):  None,
+        (uts,   "uts"):  None,
+        (ipc,   "ipc"):  None,
+        (net,   "net"):  None,
+        (pid,   "pid"):  None,
+        (user,  "user"): None,
+    }
+
+    # Save fds of current namespaces
+    for ns in [ns for ns in namespaces if ns[0]]:
+        fp = open(f"/proc/self/ns/{ns[1]}")
+        namespaces[ns] = fp
+
+    simple_unshare(mount=mount, uts=uts, ipc=ipc, net=net, pid=pid, user=user,
+                   hostname=hostname)
+    try:
+        yield
+    finally:
+        for ns in [ns for ns in namespaces if ns[0]]:
+            fp = namespaces[ns]
+            setns(fp.fileno(), 0)
+            fp.close()
diff --git a/catalyst/main.py b/catalyst/main.py
index 543895c6..93a4a0d3 100644
--- a/catalyst/main.py
+++ b/catalyst/main.py
@@ -7,14 +7,13 @@ import textwrap
 
 import toml
 
-from snakeoil.process import namespaces
-
 from DeComp.definitions import (COMPRESS_DEFINITIONS, DECOMPRESS_DEFINITIONS,
                                 CONTENTS_DEFINITIONS)
 from DeComp.contents import ContentsMap
 
 from catalyst import log
 import catalyst.config
+from catalyst.context import namespace
 from catalyst.defaults import (confdefaults, option_messages,
                                DEFAULT_CONFIG_FILE, valid_config_file_values)
 from catalyst.support import CatalystError
@@ -356,15 +355,13 @@ def _main(parser, opts):
     # use pid & user namespaces, but snakeoil's namespace module has signal
     # transfer issues (CTRL+C doesn't propagate), and user namespaces need
     # more work due to Gentoo build process (uses sudo/root/portage).
-    namespaces.simple_unshare(
-        mount=True, uts=True, ipc=True, pid=False, net=False, user=False,
-        hostname='catalyst')
+    with namespace(mount=True, uts=True, ipc=True, hostname='catalyst'):
+        # everything is setup, so the build is a go
+        try:
+            success = build_target(addlargs)
+        except KeyboardInterrupt:
+            log.critical('Catalyst build aborted due to user interrupt (Ctrl-C)')
 
-    # everything is setup, so the build is a go
-    try:
-        success = build_target(addlargs)
-    except KeyboardInterrupt:
-        log.critical('Catalyst build aborted due to user interrupt (Ctrl-C)')
     if not success:
         sys.exit(2)
     sys.exit(0)