[gentoo-portage-dev] [PATCH v3] emerge: check for writable /var/db/pkg (490732)

[Zac Medico <zmedico@gentoo.org>]

If there are packages to be merged or unmerge, then bail out early
if /var/db/pkg is not writable (in order to avoid a fatal EROFS error
which would otherwise occur later on). Behavior remains unchanged for
--pretend mode. For --ask mode, it will bail out just after the last
relevant --ask prompt.

In contrast to the writeable_check module, which operates on files just
before they are merged, the new vardbapi.writable check is performed
before anything has been built (much earlier).

X-Gentoo-Bug: 490732
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=490732
---
PATCH v3 fixes emerge --unmerge --pretend to succeed when /var/db/pkg
is not writable (--pretend actions may still be useful when operating
with a readonly filesystem).

 pym/_emerge/actions.py       | 15 +++++++++++++++
 pym/_emerge/unmerge.py       |  9 +++++++++
 pym/portage/dbapi/vartree.py | 12 ++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/pym/_emerge/actions.py b/pym/_emerge/actions.py
index 48b0826..6f7dfe0 100644
--- a/pym/_emerge/actions.py
+++ b/pym/_emerge/actions.py
@@ -428,6 +428,21 @@ def action_build(settings, trees, mtimedb,
 			# least show warnings about missed updates and such.
 			mydepgraph.display_problems()
 
+		if not Scheduler._opts_no_self_update.intersection(myopts):
+
+			eroots = set()
+			for x in mydepgraph.altlist():
+				if isinstance(x, Package) and x.operation == "merge":
+					eroots.add(x.root)
+
+			for eroot in eroots:
+				if not trees[eroot]["vartree"].dbapi.writable:
+					writemsg_level("!!! %s\n" %
+						_("Read-only file system: %s") %
+						trees[eroot]["vartree"].dbapi._dbroot,
+						level=logging.ERROR, noiselevel=-1)
+					return 1
+
 		if ("--resume" in myopts):
 			favorites=mtimedb["resume"]["favorites"]
 
diff --git a/pym/_emerge/unmerge.py b/pym/_emerge/unmerge.py
index df29000..7f6d82a 100644
--- a/pym/_emerge/unmerge.py
+++ b/pym/_emerge/unmerge.py
@@ -10,6 +10,7 @@ import textwrap
 import portage
 from portage import os
 from portage.dbapi._expand_new_virt import expand_new_virt
+from portage.localization import _
 from portage.output import bold, colorize, darkgreen, green
 from portage._sets import SETPREFIX
 from portage._sets.base import EditablePackageSet
@@ -536,6 +537,7 @@ def unmerge(root_config, myopts, unmerge_action,
 	if "--pretend" in myopts:
 		#we're done... return
 		return os.EX_OK
+
 	if "--ask" in myopts:
 		uq = UserQuery(myopts)
 		if uq.query("Would you like to unmerge these packages?",
@@ -546,6 +548,13 @@ def unmerge(root_config, myopts, unmerge_action,
 			print("Quitting.")
 			print()
 			return 128 + signal.SIGINT
+
+	if not vartree.dbapi.writable:
+		writemsg_level("!!! %s\n" %
+			_("Read-only file system: %s") % vartree.dbapi._dbroot,
+			level=logging.ERROR, noiselevel=-1)
+		return 1
+
 	#the real unmerging begins, after a short delay unless we're raging....
 	if not unmerge_action == "rage-clean" and clean_delay and not autoclean:
 		countdown(int(settings["CLEAN_DELAY"]), ">>> Unmerging")
diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index 0fd1bd9..df031cd 100644
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -33,6 +33,7 @@ portage.proxy.lazyimport.lazyimport(globals(),
 	'portage.util.env_update:env_update',
 	'portage.util.listdir:dircache,listdir',
 	'portage.util.movefile:movefile',
+	'portage.util.path:first_existing',
 	'portage.util.writeable_check:get_ro_checker',
 	'portage.util._dyn_libs.PreservedLibsRegistry:PreservedLibsRegistry',
 	'portage.util._dyn_libs.LinkageMapELF:LinkageMapELF@LinkageMap',
@@ -189,6 +190,17 @@ class vardbapi(dbapi):
 		self._cached_counter = None
 
 	@property
+	def writable(self):
+		"""
+		Check if var/db/pkg is writable, or permissions are sufficient
+		to create it if it does not exist yet.
+		@rtype: bool
+		@return: True if var/db/pkg is writable or can be created,
+			False otherwise
+		"""
+		return os.access(first_existing(self._dbroot), os.W_OK)
+
+	@property
 	def root(self):
 		warnings.warn("The root attribute of "
 			"portage.dbapi.vartree.vardbapi"
-- 
2.0.4