lifecycle: don't clean priming area if the snap is being tried

snapcraft/internal/errors.py

@@ -594,3 +594,21 @@ class SnapcraftCopyFileNotFoundError(SnapcraftError):
 
     def __init__(self, path):
         super().__init__(path=path)
+
+
+class MountPointNotFoundError(SnapcraftError):
+    fmt = (
+        'Nothing is mounted at {mount_point!r}'
+    )
+
+    def __init__(self, mount_point):
+        super().__init__(mount_point=mount_point)
+
+
+class RootNotMountedError(SnapcraftError):
+    fmt = (
+        '{root!r} is not mounted'
+    )
+
+    def __init__(self, root):
+        super().__init__(root=root)

snapcraft/internal/lifecycle/_clean.py

@@ -19,7 +19,7 @@
 import shutil
 
 from snapcraft import formatting_utils
-from snapcraft.internal import common, project_loader
+from snapcraft.internal import common, errors, project_loader, mountinfo
 from . import constants
 
 
@@ -112,11 +112,25 @@ def _cleanup_common_directories_for_step(step, project_options, parts=None):
 
     index = common.COMMAND_ORDER.index(step)
 
+    being_tried = False
     if index <= common.COMMAND_ORDER.index('prime'):
-        # Remove the priming area.
+        # Remove the priming area. Only remove the actual 'prime' directory if
+        # it's NOT being used in 'snap try'. We'll know that if it's
+        # bind-mounted somewhere.
+        mounts = mountinfo.MountInfo()
+        try:
+            mounts.for_root(project_options.prime_dir)
+        except errors.RootNotMountedError:
+            remove_dir = True
+            message = 'Cleaning up priming area'
+        else:
+            remove_dir = False
+            message = ("Cleaning up priming area, but not removing as it's in "
+                       "use by 'snap try'")
+            being_tried = True
         _cleanup_common(
-            project_options.prime_dir, 'prime', 'Cleaning up priming area',
-            parts)
+            project_options.prime_dir, 'prime', message, parts,
+            remove_dir=remove_dir)
 
     if index <= common.COMMAND_ORDER.index('stage'):
         # Remove the staging area.
@@ -131,15 +145,24 @@ def _cleanup_common_directories_for_step(step, project_options, parts=None):
             parts)
         _cleanup_internal_snapcraft_dir()
 
-    _remove_directory_if_empty(project_options.prime_dir)
+    if not being_tried:
+        _remove_directory_if_empty(project_options.prime_dir)
     _remove_directory_if_empty(project_options.stage_dir)
     _remove_directory_if_empty(project_options.parts_dir)
 
 
-def _cleanup_common(directory, step, message, parts):
+def _cleanup_common(directory, step, message, parts, *, remove_dir=True):
     if os.path.isdir(directory):
         logger.info(message)
-        shutil.rmtree(directory)
+        if remove_dir:
+            shutil.rmtree(directory)
+        else:
+            # Don't delete the parent directory, but delete its contents
+            for f in os.scandir(directory):
+                if f.is_dir(follow_symlinks=False):
+                    shutil.rmtree(f.path)
+                elif f.is_file(follow_symlinks=False):
+                    os.remove(f.path)
     for part in parts:
         part.mark_cleaned(step)
 

snapcraft/internal/mountinfo.py

@@ -0,0 +1,77 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright (C) 2018 Canonical Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import collections
+import contextlib
+import csv
+from typing import Dict, List  # noqa: F401
+
+from snapcraft.internal import errors
+
+
+class Mount:
+    """A class to provide programmatic access to a specific mountpoint"""
+
+    def __init__(self, mountinfo_row: List[str]) -> None:
+        # Parse the row according to section 3.5 of
+        # https://www.kernel.org/doc/Documentation/filesystems/proc.txt
+        self.mount_id = mountinfo_row[0]
+        self.parent_id = mountinfo_row[1]
+        self.st_dev = mountinfo_row[2]
+        self.root = mountinfo_row[3]
+        self.mount_point = mountinfo_row[4]
+        self.mount_options = mountinfo_row[5]
+        separator_index = mountinfo_row.index('-')
+        self.optional_fields = mountinfo_row[6:separator_index]
+        self.filesystem_type = mountinfo_row[separator_index+1]
+        self.mount_source = mountinfo_row[separator_index+2]
+        self.super_options = mountinfo_row[separator_index+3]
+
+
+class MountInfo:
+    """A class to provide programmatic access to /proc/self/mountinfo"""
+
+    def __init__(self, *,
+                 mountinfo_file: str = '/proc/self/mountinfo') -> None:
+        """Create a new MountInfo instance.
+
+        :param str mountinfo_file: Path to mountinfo file to be parsed.
+        """
+        # Maintain two dicts pointing to the same underlying objects:
+        # a dict of mount points to Mounts, and a dict of roots to Mounts.
+        self._mount_point_mounts = {}  # type: Dict[str, Mount]
+        root_mounts = collections.defaultdict(list)  # type: Dict[str, List[Mount]]  # noqa
+
+        with contextlib.suppress(FileNotFoundError):
+            with open(mountinfo_file) as f:
+                for row in csv.reader(f, delimiter=' '):
+                    mount = Mount(row)
+                    self._mount_point_mounts[mount.mount_point] = mount
+                    root_mounts[mount.root].append(mount)
+
+        self._root_mounts = dict(root_mounts)
+
+    def for_mount_point(self, mount_point: str) -> Mount:
+        try:
+            return self._mount_point_mounts[mount_point]
+        except KeyError:
+            raise errors.MountPointNotFoundError(mount_point)
+
+    def for_root(self, root: str) -> List[Mount]:
+        try:
+            return self._root_mounts[root]
+        except KeyError:
+            raise errors.RootNotMountedError(root)

tests/unit/test_lifecycle.py

@@ -765,6 +765,20 @@ def test_clean_removes_global_state(self):
             os.path.join('snap', '.snapcraft'),
             Not(DirExists()))
 
+    @mock.patch('snapcraft.internal.mountinfo.MountInfo.for_root')
+    def test_clean_leaves_prime_alone_for_tried(self, mock_for_root):
+        self.make_snapcraft_yaml(
+            textwrap.dedent("""\
+                parts:
+                  test-part:
+                    plugin: nil
+                """))
+        lifecycle.execute('prime', self.project_options)
+        lifecycle.clean(self.project_options, parts=None)
+        self.assertThat(
+            'prime', DirExists(),
+            'Expected prime directory to remain after cleaning for tried snap')
+
 
 class RecordSnapcraftYamlTestCase(BaseLifecycleTestCase):
 

tests/unit/test_mountinfo.py

@@ -0,0 +1,114 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright (C) 2018 Canonical Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from textwrap import dedent
+
+from testtools.matchers import Equals, HasLength
+
+from snapcraft.internal import (
+    errors,
+    mountinfo,
+)
+
+from tests import unit
+
+
+class MountInfoTestCase(unit.TestCase):
+
+    def _write_mountinfo(self, contents):
+        path = 'mountinfo'
+        with open(path, 'w') as f:
+            f.write(contents)
+        return path
+
+    def test_mountinfo_by_root(self):
+        mounts = mountinfo.MountInfo(mountinfo_file=self._write_mountinfo(
+            dedent("""\
+                23 28 0:4 / /proc rw,nosuid,nodev,noexec,relatime shared:14 - proc proc rw
+                1341 28 7:6 / /snap/snapcraft/1 ro,nodev,relatime shared:39 - squashfs /dev/loop6 ro
+                1455 28 253:0 /test-snap/prime /snap/test-snap/x1 ro,relatime shared:1 - ext4 /dev/mapper/foo rw,errors=remount-ro,data=ordered
+                """)))  # noqa
+
+        root_mounts = mounts.for_root('/')
+        for mount_point in ('/proc', '/snap/snapcraft/1'):
+            self.assertTrue(
+                any(m for m in root_mounts if m.mount_point == mount_point),
+                'Expected {!r} to be included in root mounts'.format(
+                    mount_point))
+
+        test_snap_mounts = mounts.for_root('/test-snap/prime')
+        self.assertThat(test_snap_mounts, HasLength(1))
+        self.expectThat(
+            test_snap_mounts[0].mount_point, Equals('/snap/test-snap/x1'))
+
+    def test_mountinfo_by_mount_point(self):
+        mounts = mountinfo.MountInfo(mountinfo_file=self._write_mountinfo(
+            dedent("""\
+                23 28 0:4 / /proc rw,nosuid,nodev,noexec,relatime shared:14 - proc proc rw
+                1341 28 7:6 / /snap/snapcraft/1 ro,nodev,relatime shared:39 - squashfs /dev/loop6 ro
+                1455 28 253:0 /test-snap/prime /snap/test-snap/x1 ro,relatime shared:1 - ext4 /dev/mapper/foo rw,errors=remount-ro,data=ordered
+                """)))  # noqa
+
+        mount = mounts.for_mount_point('/proc')
+        self.assertThat(mount.mount_id, Equals('23'))
+        self.assertThat(mount.parent_id, Equals('28'))
+        self.assertThat(mount.st_dev, Equals('0:4'))
+        self.assertThat(mount.root, Equals('/'))
+        self.assertThat(mount.mount_point, Equals('/proc'))
+        self.assertThat(
+            mount.mount_options, Equals('rw,nosuid,nodev,noexec,relatime'))
+        self.assertThat(mount.optional_fields, Equals(['shared:14']))
+        self.assertThat(mount.filesystem_type, Equals('proc'))
+        self.assertThat(mount.mount_source, Equals('proc'))
+        self.assertThat(mount.super_options, Equals('rw'))
+
+        mount = mounts.for_mount_point('/snap/snapcraft/1')
+        self.assertThat(mount.mount_id, Equals('1341'))
+        self.assertThat(mount.parent_id, Equals('28'))
+        self.assertThat(mount.st_dev, Equals('7:6'))
+        self.assertThat(mount.root, Equals('/'))
+        self.assertThat(mount.mount_point, Equals('/snap/snapcraft/1'))
+        self.assertThat(mount.mount_options, Equals('ro,nodev,relatime'))
+        self.assertThat(mount.optional_fields, Equals(['shared:39']))
+        self.assertThat(mount.filesystem_type, Equals('squashfs'))
+        self.assertThat(mount.mount_source, Equals('/dev/loop6'))
+        self.assertThat(mount.super_options, Equals('ro'))
+
+        mount = mounts.for_mount_point('/snap/test-snap/x1')
+        self.assertThat(mount.mount_id, Equals('1455'))
+        self.assertThat(mount.parent_id, Equals('28'))
+        self.assertThat(mount.st_dev, Equals('253:0'))
+        self.assertThat(mount.root, Equals('/test-snap/prime'))
+        self.assertThat(mount.mount_point, Equals('/snap/test-snap/x1'))
+        self.assertThat(mount.mount_options, Equals('ro,relatime'))
+        self.assertThat(mount.optional_fields, Equals(['shared:1']))
+        self.assertThat(mount.filesystem_type, Equals('ext4'))
+        self.assertThat(mount.mount_source, Equals('/dev/mapper/foo'))
+        self.assertThat(
+            mount.super_options, Equals('rw,errors=remount-ro,data=ordered'))
+
+    def test_mountinfo_missing_root(self):
+        mounts = mountinfo.MountInfo(mountinfo_file=self._write_mountinfo(''))
+        raised = self.assertRaises(
+            errors.RootNotMountedError, mounts.for_root, 'test-root')
+        self.assertThat(raised.root, Equals('test-root'))
+
+    def test_mountinfo_missing_mount_point(self):
+        mounts = mountinfo.MountInfo(mountinfo_file=self._write_mountinfo(''))
+        raised = self.assertRaises(
+            errors.MountPointNotFoundError, mounts.for_mount_point,
+            'test-root')
+        self.assertThat(raised.mount_point, Equals('test-root'))