[gentoo-portage-dev] [PATCH v6] Test for read-only filesystems, bail out during preinst if there are any which will be written to and display a useful error message. Fixes bug 378869.

[Chris Reffett <creffett@gentoo.org>]

v2: Reformat, add a function to return an appropriate read-only checker
for the operating system, so that this can be extended to other OSes.

v3: minor formatting tweaks from bernalex, including use os.path.join()
instead of string concatenation

v4: Update copyright header, change the code in rochecker to open with
io.open in order to not break on non-ascii characters as reported by
Arfrever. Change get_ro_checker to use a dict as suggested by vapier.

v5: Fix comment format as requested by vapier.

v6: Change linux_ro_checker to use set.intersection instead of the
longer check-and-append system as suggested by vapier.
---
 pym/portage/dbapi/vartree.py  | 34 +++++++++++++++++-
 pym/portage/util/rochecker.py | 80 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+), 1 deletion(-)
 create mode 100644 pym/portage/util/rochecker.py

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index ed62323..cf6781b 100644
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -1,4 +1,4 @@
-# Copyright 1998-2013 Gentoo Foundation
+# Copyright 1998-2014 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 from __future__ import unicode_literals
@@ -32,6 +32,7 @@ portage.proxy.lazyimport.lazyimport(globals(),
 	'portage.util.env_update:env_update',
 	'portage.util.listdir:dircache,listdir',
 	'portage.util.movefile:movefile',
+	'portage.util.rochecker:get_ro_checker',
 	'portage.util._dyn_libs.PreservedLibsRegistry:PreservedLibsRegistry',
 	'portage.util._dyn_libs.LinkageMapELF:LinkageMapELF@LinkageMap',
 	'portage.util._async.SchedulerInterface:SchedulerInterface',
@@ -3508,6 +3509,8 @@ class dblink(object):
 		
 		This function does the following:
 		
+		calls get_ro_checker to retrieve a function for checking whether Portage
+		will write to a read-only filesystem, then runs it against the directory list
 		calls self._preserve_libs if FEATURES=preserve-libs
 		calls self._collision_protect if FEATURES=collision-protect
 		calls doebuild(mydo=pkg_preinst)
@@ -3685,6 +3688,7 @@ class dblink(object):
 			eagain_error = False
 
 			myfilelist = []
+			mydirlist = []
 			mylinklist = []
 			paths_with_newlines = []
 			def onerror(e):
@@ -3717,6 +3721,9 @@ class dblink(object):
 					unicode_errors.append(new_parent[ed_len:])
 					break
 
+				relative_path = parent[srcroot_len:]
+				mydirlist.append(os.path.join("/", relative_path))
+
 				for fname in files:
 					try:
 						fname = _unicode_decode(fname,
@@ -3829,6 +3836,31 @@ class dblink(object):
 			for other in others_in_slot])
 		prepare_build_dirs(settings=self.settings, cleanup=cleanup)
 
+		# Check for read-only filesystems.
+		ro_checker = get_ro_checker()
+		rofilesystems = ro_checker(mydirlist)
+
+		if rofilesystems:
+			msg = _("One or more files installed to this package are "
+				"set to be installed to read-only filesystems. "
+				"Please mount the following filesystems as read-write "
+				"and retry.")
+			msg = textwrap.wrap(msg, 70)
+			msg.append("")
+			for f in rofilesystems:
+				msg.append("\t%s" % os.path.join(destroot,
+					f.lstrip(os.path.sep)))
+			msg.append("")
+			self._elog("eerror", "preinst", msg)
+
+			msg = _("Package '%s' NOT merged due to read-only file systems.") % \
+				self.settings.mycpv
+			msg += _(" If necessary, refer to your elog "
+				"messages for the whole content of the above message.")
+			msg = textwrap.wrap(msg, 70)
+			eerror(msg)
+			return 1
+
 		# check for package collisions
 		blockers = self._blockers
 		if blockers is None:
diff --git a/pym/portage/util/rochecker.py b/pym/portage/util/rochecker.py
new file mode 100644
index 0000000..c13bdfc
--- /dev/null
+++ b/pym/portage/util/rochecker.py
@@ -0,0 +1,80 @@
+#-*- coding:utf-8 -*-
+# Copyright 2014 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+"""
+Methods to check whether Portage is going to write to read-only filesystems.
+Since the methods are not portable across different OSes, each OS needs its
+own method. To expand RO checking for different OSes, add a method which
+accepts a list of directories and returns a list of mounts which need to be
+remounted RW, then add "elif ostype == (the ostype value for your OS)" to
+get_ro_checker().
+"""
+from __future__ import unicode_literals
+
+import io
+import logging
+import re
+
+from portage import _encodings
+from portage.util import writemsg_level
+from portage.localization import _
+from portage.data import ostype
+
+
+def get_ro_checker():
+	"""
+	Uses the system type to find an appropriate method for testing whether Portage
+	is going to write to any read-only filesystems.
+
+	@return:
+	1. A method for testing for RO filesystems appropriate to the current system.
+	"""
+	return _CHECKERS.get(ostype, empty_ro_checker)
+
+
+def linux_ro_checker(dir_list):
+	"""
+	Use /proc/mounts to check that no directories installed by the ebuild are set
+	to be installed to a read-only filesystem.
+
+	@param dir_list: A list of directories installed by the ebuild.
+	@type dir_list: List
+	@return:
+	1. A list of filesystems which are both set to be written to and are mounted
+	read-only, may be empty.
+	"""
+	ro_filesystems = set()
+	ro_filesystems_written = set()
+
+	try:
+		with io.open("/proc/mounts", mode='r', encoding=_encodings['content'],
+			errors='replace') as f:
+			roregex = re.compile(r'(\A|,)ro(\Z|,)')
+			for line in f:
+				if roregex.search(line.split(" ")[3].strip()) is not None:
+					romount = line.split(" ")[1].strip()
+					ro_filesystems.add(romount)
+
+	# If /proc/mounts can't be read, assume that there are no RO
+	# filesystems and return.
+	except EnvironmentError:
+		writemsg_level(_("!!! /proc/mounts cannot be read"),
+			level=logging.WARNING, noiselevel=-1)
+		return []
+
+	return set.intersection(ro_filesystems, set(dir_list))
+
+
+def empty_ro_checker(dir_list):
+	"""
+	Always returns [], this is the fallback function if the system does not have
+	an ro_checker method defined.
+	"""
+	return []
+
+
+# _CHECKERS is a map from ostype output to the appropriate function to return
+# in get_ro_checker.
+_CHECKERS = {
+	"Linux": linux_ro_checker,
+}
-- 
1.8.5.3