[gentoo-portage-dev] [PATCH] Check for and report read-only filesystems

[gentoo-portage-dev] [PATCH] Check for and report read-only filesystems

[Chris Reffett]

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Hi all,
Attached is a patch to test if Portage is going to write to a
read-only filesystem and print out the list of filesystems that need
to be remounted RW. This leaves ${D} intact rather than having some
files moved before hitting the RO filesystem. Fixes bug 378869. Since
git.overlays.gentoo.org is down, I haven't had the chance to rebase
this against latest, but I can resubmit if it doesn't cleanly apply.
This is my first patch to the list, so I apologize if I didn't submit
correctly.

Chris Reffett
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From c464ac5e0007a087def9a96efea9653e508e57c1 Mon Sep 17 00:00:00 2001
From: Chris Reffett <creffett@gentoo.org>
Date: Fri, 10 Jan 2014 09:03:26 -0500
Subject: [PATCH] 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.

---
 pym/portage/dbapi/vartree.py       | 31 ++++++++++++++++++++++++
 pym/portage/util/checkwriteable.py | 49 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 pym/portage/util/checkwriteable.py

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index ed62323..8ae7014 100644
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -28,6 +28,7 @@ portage.proxy.lazyimport.lazyimport(globals(),
 	'portage.util:apply_secpass_permissions,ConfigProtect,ensure_dirs,' + \
 		'writemsg,writemsg_level,write_atomic,atomic_ofstream,writedict,' + \
 		'grabdict,normalize_path,new_protect_filename',
+	'portage.util.checkwriteable:check_dirs_writeable',
 	'portage.util.digraph:digraph',
 	'portage.util.env_update:env_update',
 	'portage.util.listdir:dircache,listdir',
@@ -3508,6 +3509,8 @@ class dblink(object):
 		
 		This function does the following:
 		
+		calls check_dirs_writeable to verify that no files will be
+		written to read-only filesystems
 		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("/" + relative_path)
+
 				for fname in files:
 					try:
 						fname = _unicode_decode(fname,
@@ -3829,6 +3836,30 @@ class dblink(object):
 			for other in others_in_slot])
 		prepare_build_dirs(settings=self.settings, cleanup=cleanup)
 
+		# Check for read-only filesystems
+		rofilesystems = check_dirs_writeable(mydirlist)
+
+		if rofilesystems:
+			msg = _("One or more files installed to this package are "
+				"set to be installed to read-only filesystems. "
+				"Please mount the filesystems below 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/checkwriteable.py b/pym/portage/util/checkwriteable.py
new file mode 100644
index 0000000..9bd9056
--- /dev/null
+++ b/pym/portage/util/checkwriteable.py
@@ -0,0 +1,49 @@
+#-*- coding:utf-8 -*-
+# Copyright 2014 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+from __future__ import unicode_literals
+
+import re
+
+from portage.util import writemsg
+from portage.localization import _
+
+
+def check_dirs_writeable(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: 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 open("/proc/mounts") as procmounts:
+			roregex = re.compile(r'(\A|,)ro(\Z|,)')
+			for line in procmounts:
+				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(_("!!! /proc/mounts cannot be read"))
+		return []
+
+	if not ro_filesystems:
+		return ro_filesystems
+
+	for directory in dir_list:
+		for filesystem in ro_filesystems:
+			if re.match(filesystem, directory):
+				ro_filesystems_written.add(filesystem)
+
+	return ro_filesystems_written
-- 
1.8.5.1

Re: [gentoo-portage-dev] [PATCH] Check for and report read-only filesystems

[Brian Dolbec]

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On Fri, 2014-01-10 at 22:07 -0500, Chris Reffett wrote:
> Hi all,
> Attached is a patch to test if Portage is going to write to a
> read-only filesystem and print out the list of filesystems that need
> to be remounted RW. This leaves ${D} intact rather than having some
> files moved before hitting the RO filesystem. Fixes bug 378869. Since
> git.overlays.gentoo.org is down, I haven't had the chance to rebase
> this against latest, but I can resubmit if it doesn't cleanly apply.
> This is my first patch to the list, so I apologize if I didn't submit
> correctly.
> 
> Chris Reffett


yeah, patch looks good.

Only thing I didn't like is the return 1  IS that suppose to be True or
sys.exit() value?

If that is what the module was using, then it's ok.  Personally I'm not
a fan of using 0, 1 for False, True.

But that will come later...

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Re: [gentoo-portage-dev] [PATCH] Check for and report read-only filesystems

[Chris Reffett]

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Hash: SHA1

On 01/11/2014 12:09 AM, Brian Dolbec wrote:
> On Fri, 2014-01-10 at 22:07 -0500, Chris Reffett wrote:
>> Hi all, Attached is a patch to test if Portage is going to write
>> to a read-only filesystem and print out the list of filesystems
>> that need to be remounted RW. This leaves ${D} intact rather than
>> having some files moved before hitting the RO filesystem. Fixes
>> bug 378869. Since git.overlays.gentoo.org is down, I haven't had
>> the chance to rebase this against latest, but I can resubmit if
>> it doesn't cleanly apply. This is my first patch to the list, so
>> I apologize if I didn't submit correctly.
>> 
>> Chris Reffett
> 
> 
> yeah, patch looks good.
> 
> Only thing I didn't like is the return 1  IS that suppose to be
> True or sys.exit() value?
> 
> If that is what the module was using, then it's ok.  Personally I'm
> not a fan of using 0, 1 for False, True.
> 
> But that will come later...
> 
That was just following the style of the rest of the module, for
example a collision will return 1. This can be added to the "stuff to
be fixed up in future patches" list.

Chris Reffett
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Re: [gentoo-portage-dev] [PATCH] Check for and report read-only filesystems

[Mike Frysinger]

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On Friday 10 January 2014 22:07:52 Chris Reffett wrote:
> Attached is a patch to test if Portage is going to write to a
> read-only filesystem and print out the list of filesystems that need
> to be remounted RW. This leaves ${D} intact rather than having some
> files moved before hitting the RO filesystem. Fixes bug 378869. Since
> git.overlays.gentoo.org is down, I haven't had the chance to rebase
> this against latest, but I can resubmit if it doesn't cleanly apply.
> This is my first patch to the list, so I apologize if I didn't submit
> correctly.

please use `git send-email` to post patches.  attaching them makes things 
harder to review.

> --- /dev/null
> +++ b/pym/portage/util/checkwriteable.py
>
> +		with open("/proc/mounts") as procmounts:

this won't work on non-Linux systems

also, as a general style thing, unless there's a real need for the var to have 
a "full" name, just use "f" or "fp"

> +			roregex = re.compile(r'(\A|,)ro(\Z|,)')
> +			for line in procmounts:
> +				if roregex.search(line.split(" ")[3].strip()) is not None:
> +					romount = line.split(" ")[1].strip()
> +					ro_filesystems.add(romount)

ad hoc parsing of /proc/mounts isn't a good thing.  at the risk of over 
engineering, there should be a func that would take care of expanding the 
mount paths into a list of namedcollections (one per mount).  then you simply 
walk it looking at its options.

> +	for directory in dir_list:
> +		for filesystem in ro_filesystems:
> +			if re.match(filesystem, directory):
> +				ro_filesystems_written.add(filesystem)

there's no need to use re and in fact you don't want to.  you're looking at 
wrong strings here, not regexes.
-mike

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[gentoo-portage-dev] [PATCH v2] 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]

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.
---
 pym/portage/dbapi/vartree.py  | 32 +++++++++++++++++
 pym/portage/util/rochecker.py | 81 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 pym/portage/util/rochecker.py

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index ed62323..c77cf07 100644
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -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("/" + 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_func = get_ro_checker()
+		rofilesystems = ro_checker_func(mydirlist)
+
+		if rofilesystems:
+			msg = _("One or more files installed to this package are "
+				"set to be installed to read-only filesystems. "
+				"Please mount the filesystems below 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..67e8131
--- /dev/null
+++ b/pym/portage/util/rochecker.py
@@ -0,0 +1,81 @@
+#-*- 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 logging
+import re
+
+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
+	"""
+	if ostype == "Linux":
+		return linux_ro_checker
+	else:
+		return 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: 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 open("/proc/mounts") 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 []
+
+	if not ro_filesystems:
+		return ro_filesystems
+
+	for directory in dir_list:
+		for filesystem in ro_filesystems:
+			if filesystem == directory:
+				ro_filesystems_written.add(filesystem)
+
+	return ro_filesystems_written
+
+
+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 []
-- 
1.8.5.1

[gentoo-portage-dev] [PATCH v3] 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]

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
---
 pym/portage/dbapi/vartree.py  | 32 +++++++++++++++++
 pym/portage/util/rochecker.py | 81 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 pym/portage/util/rochecker.py

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index ed62323..917634f 100644
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -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..67e8131
--- /dev/null
+++ b/pym/portage/util/rochecker.py
@@ -0,0 +1,81 @@
+#-*- 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 logging
+import re
+
+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
+	"""
+	if ostype == "Linux":
+		return linux_ro_checker
+	else:
+		return 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: 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 open("/proc/mounts") 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 []
+
+	if not ro_filesystems:
+		return ro_filesystems
+
+	for directory in dir_list:
+		for filesystem in ro_filesystems:
+			if filesystem == directory:
+				ro_filesystems_written.add(filesystem)
+
+	return ro_filesystems_written
+
+
+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 []
-- 
1.8.5.1

Re: [gentoo-portage-dev] [PATCH v3] 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.

[Mike Frysinger]

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On Saturday 18 January 2014 21:00:48 Chris Reffett wrote:
> --- /dev/null
> +++ b/pym/portage/util/rochecker.py
> @@ -0,0 +1,81 @@
> +#-*- 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

prefer OSes -> OS's

> +get_ro_checker()
> +"""

period at the end

> +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
> +	"""

not a new issue, but we really need to get away from this style and use 
PEP257.  someone feel like fixing that in the code base ? :)

> +	if ostype == "Linux":
> +		return linux_ro_checker
> +	else:
> +		return empty_ro_checker

isn't this a glorified dict ?

_CHECKERS = {
	'Linux': linux_ro_checker,
}

def get_ro_checker()
	return _CHECKERS.get(ostype, empty_ro_checker)
-mike

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Re: [gentoo-portage-dev] [PATCH v3] 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.

[Alexander Berntsen]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

On 19/01/14 10:17, Mike Frysinger wrote:
> prefer OSes -> OS's
That's just not proper English. It makes no sense. Please don't prefer
that. If for nothing else, then to prevent me from sighing whenever I
have to read it.

> not a new issue, but we really need to get away from this style and
> use PEP257.  someone feel like fixing that in the code base ? :)
I agree. If you give me at least a week (won't have time until next
weekend), I can look into it.
- -- 
Alexander
alexander@plaimi.net
http://plaimi.net/~alexander
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Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

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hQqnReHPRwLpDNRccOcA/jUODDanycVmNLpD/rjkYnKyllnbUSIxduYuMcJFqXme
=vaDs
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Re: [gentoo-portage-dev] [PATCH v3] 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.

[Alec Warner]

[-- Attachment #1: Type: text/plain, Size: 1568 bytes --]

On Sun, Jan 19, 2014 at 2:39 AM, Alexander Berntsen <alexander@plaimi.net>wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
>
> On 19/01/14 10:17, Mike Frysinger wrote:
> > prefer OSes -> OS's
> That's just not proper English. It makes no sense. Please don't prefer
> that. If for nothing else, then to prevent me from sighing whenever I
> have to read it.
>

The bikeshed should be red! Be happy in the fact that this bit has no
significant bearing on the code and just pick one.


> > not a new issue, but we really need to get away from this style and
> > use PEP257.  someone feel like fixing that in the code base ? :)
> I agree. If you give me at least a week (won't have time until next
> weekend), I can look into it.
>

Sorry, my fault. I added docstrings in 2006 (looks like the first one was
vercmp in
http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=blobdiff;f=pym/portage_versions.py;h=8e58c2f47766c0ed6c007c0cba1fccebca7d4eb4;hp=ec01773ad199a87d7906eb3862a14b9c8102fc29;hb=cfc497009e6054a5403461be676bb94deebbbf50;hpb=53f14db70339391fb13ca0adab353645f84be3f2)
I'm happy for these to change. ;p

-A



> - --

Alexander
> alexander@plaimi.net
> http://plaimi.net/~alexander
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v2.0.22 (GNU/Linux)
> Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
>
> iF4EAREIAAYFAlLbq10ACgkQRtClrXBQc7U7MAD/Yl2pd0ood3UKmvNMg9gdWMsw
> hQqnReHPRwLpDNRccOcA/jUODDanycVmNLpD/rjkYnKyllnbUSIxduYuMcJFqXme
> =vaDs
> -----END PGP SIGNATURE-----
>
>

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Re: [gentoo-portage-dev] [PATCH v3] 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.

[Mike Frysinger]

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On Sunday 19 January 2014 05:39:25 Alexander Berntsen wrote:
> On 19/01/14 10:17, Mike Frysinger wrote:
> > prefer OSes -> OS's
> 
> That's just not proper English.

i don't think that phrase means what you think it means.  if you're wishing 
for English to be a standard, then you're in for a rude surprise.

> It makes no sense.

of course it does.

> Please don't prefer
> that. If for nothing else, then to prevent me from sighing whenever I
> have to read it.

https://en.wikipedia.org/wiki/English_plurals#Plurals_of_letters_and_abbreviations
-mike

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Re: [gentoo-portage-dev] [PATCH v3] 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.

[Gordon Pettey]

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If your going to make that argumint, ewe mite a's well right the
documentation in LOL-1337. Encouraging bad grammar in documentation just
make's thing's harder for everybody.


On Mon, Jan 20, 2014 at 9:28 PM, Mike Frysinger <vapier@gentoo.org> wrote:

> On Sunday 19 January 2014 05:39:25 Alexander Berntsen wrote:
> > On 19/01/14 10:17, Mike Frysinger wrote:
> > > prefer OSes -> OS's
> >
> > That's just not proper English.
>
> i don't think that phrase means what you think it means.  if you're wishing
> for English to be a standard, then you're in for a rude surprise.
>
> > It makes no sense.
>
> of course it does.
>
> > Please don't prefer
> > that. If for nothing else, then to prevent me from sighing whenever I
> > have to read it.
>
>
> https://en.wikipedia.org/wiki/English_plurals#Plurals_of_letters_and_abbreviations
> -mike
>

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Re: [gentoo-portage-dev] [PATCH v3] 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.

[Mike Frysinger]

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On Monday 20 January 2014 22:53:25 Gordon Pettey wrote:
> If your going to make that argumint, ewe mite a's well right the
> documentation in LOL-1337. Encouraging bad grammar in documentation just
> make's thing's harder for everybody.

(1) don't top post
(2) you posted nothing to support your assertion that using 's to pluralize 
acronyms is "bad grammar"
(3) i posted information that shows it's an accepted form

so if you don't have anything useful to post, then just refrain from doing so
-mike

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[gentoo-portage-dev] [PATCH v4] 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]

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.
---
 pym/portage/dbapi/vartree.py  | 34 ++++++++++++++++-
 pym/portage/util/rochecker.py | 87 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 120 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..22cf222 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..2bbfe9d
--- /dev/null
+++ b/pym/portage/util/rochecker.py
@@ -0,0 +1,87 @@
+#-*- 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: 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 []
+
+	if not ro_filesystems:
+		return ro_filesystems
+
+	for directory in dir_list:
+		for filesystem in ro_filesystems:
+			if filesystem == directory:
+				ro_filesystems_written.add(filesystem)
+
+	return ro_filesystems_written
+
+
+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 []
+
+
+# A map from ostype output to the appropriate function to return in get_ro_checker
+_CHECKERS = {
+	"Linux": linux_ro_checker,
+}
-- 
1.8.5.1

Re: [gentoo-portage-dev] [PATCH v4] 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.

[Mike Frysinger]

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On Monday 20 January 2014 19:50:54 Chris Reffett wrote:
> +		# Check for read-only filesystems

please use full sentences.  that means putting a period at the end.  this 
applies to many additions in this patch.

> +	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)

pretty sure the body of this with block is indented one too many times
-mike

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[gentoo-portage-dev] [PATCH v5] 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]

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.
---
 pym/portage/dbapi/vartree.py  | 34 ++++++++++++++++-
 pym/portage/util/rochecker.py | 88 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 121 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..2d3c89f
--- /dev/null
+++ b/pym/portage/util/rochecker.py
@@ -0,0 +1,88 @@
+#-*- 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 []
+
+	if not ro_filesystems:
+		return ro_filesystems
+
+	for directory in dir_list:
+		for filesystem in ro_filesystems:
+			if filesystem == directory:
+				ro_filesystems_written.add(filesystem)
+
+	return ro_filesystems_written
+
+
+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

Re: [gentoo-portage-dev] [PATCH v5] 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.

[Mike Frysinger]

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On Monday 20 January 2014 23:00:31 Chris Reffett wrote:
> +	if not ro_filesystems:
> +		return ro_filesystems
> +
> +	for directory in dir_list:
> +		for filesystem in ro_filesystems:
> +			if filesystem == directory:
> +				ro_filesystems_written.add(filesystem)
> +
> +	return ro_filesystems_written

is this just the intersection of two sets ?  so all this logic could be:
	return ro_filesystems ^ set(dir_list)
-mike

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[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]

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