Kay Sievers
bf9d233f78
If a 'change' event is supposed to remove created symlinks, we create a new device structure from the sysfs device and fill it with the list of links, to compute the delta of the old and new list of links to apply. If the device is already 'remove'd by the kernel though, udev fails to create the device structure, so the links are not removed properly. > From: Neil Brown <nfbrown@suse.com> > Date: Thu, 8 Nov 2012 10:39:06 +0100 > Subject: [PATCH] If a 'change' event does not get handled by udev until > after the device has subsequently disappeared, udev mis-handles > it. This can happen with 'md' devices which emit a change > event and then a remove event when they are stopped. It is > normally only noticed if udev is very busy (lots of arrays > being stopped at once) or the machine is otherwise loaded > and reponding slowly. > > There are two problems. > > 1/ udev_device_new_from_syspath() will refuse to create the device > structure if the device does not exist in /sys, and particularly if > the uevent file does not exist. > If a 'db' file does exist, that is sufficient evidence that the device > is genuine and should be created. Equally if we have just received an > event from the kernel about the device, it must be real. > > This patch just disabled the test for the 'uevent' file, it doesn't > try imposing any other tests - it isn't clear that they are really > needed. > > 2/ udev_event_execute_rules() calls udev_device_read_db() on a 'device' > structure that is largely uninitialised and in particular does not > have the 'subsystem' set. udev_device_read_db() needs the subsystem > so it tries to read the 'subsystem' symlink out of sysfs. If the > device is already deleted, this naturally fails. > udev_event_execute_rules() knows the subsystem (as it was in the > event message) so this patch simply sets the subsystem for the device > structure to be loaded to match the subsystem of the device structure > that is handling the event. > > With these two changes, deleted handling of change events will still > correctly remove any symlinks that are not needed any more. Use udev_device_new() instead of allowing udev_device_new_from_syspath() to proceed without a sysfs device.
systemd System and Service Manager
DETAILS:
http://0pointer.de/blog/projects/systemd.html
WEB SITE:
http://www.freedesktop.org/wiki/Software/systemd
GIT:
git://anongit.freedesktop.org/systemd/systemd
ssh://git.freedesktop.org/git/systemd/systemd
GITWEB:
http://cgit.freedesktop.org/systemd/systemd
MAILING LIST:
http://lists.freedesktop.org/mailman/listinfo/systemd-devel
http://lists.freedesktop.org/mailman/listinfo/systemd-commits
IRC:
#systemd on irc.freenode.org
BUG REPORTS:
https://bugs.freedesktop.org/enter_bug.cgi?product=systemd
AUTHOR:
Lennart Poettering
Kay Sievers
...and many others
LICENSE:
LGPLv2.1+ for all code
- except sd-daemon.[ch] and sd-readahead.[ch] which are MIT
- except src/udev/ which is GPLv2.0+
REQUIREMENTS:
Linux kernel >= 2.6.39
with devtmpfs
with cgroups (but it's OK to disable all controllers)
optional but strongly recommended: autofs4, ipv6
dbus >= 1.4.0
libcap
libblkid >= 2.20 (from util-linux)
libkmod >= 5
PAM >= 1.1.2 (optional)
libcryptsetup (optional)
libgcrypt (optional)
libaudit (optional)
libacl (optional)
libattr (optional)
libselinux (optional)
liblzma (optional)
tcpwrappers (optional)
libgcrypt (optional)
libqrencode (optional)
libmicrohttpd (optional)
When you build from git you need the following additional dependencies:
docbook-xsl
xsltproc
automake
autoconf
libtool
intltool
gperf
gtkdocize (optional)
python (optional)
make, gcc, and similar tools
During runtime you need the following dependencies:
util-linux > v2.18 (requires fsck -l, agetty -s)
sulogin (from sysvinit-tools, optional but recommended)
dracut (optional)
When systemd-hostnamed is used it is strongly recommended to
install nss-myhostname to ensure that in a world of
dynamically changing hostnames the hostname stays resolvable
under all circumstances. In fact, systemd-hostnamed will warn
if nss-myhostname is not installed. Packagers are encouraged to
add a dependency on nss-myhostname to the package that
includes systemd-hostnamed.
Note that D-Bus can link against libsystemd-login.so, which
results in a cyclic build dependency. To accommodate for this
please build D-Bus without systemd first, then build systemd,
then rebuild D-Bus with systemd support.
WARNINGS:
systemd will warn you during boot if /etc/mtab is not a
symlink to /proc/mounts. Please ensure that /etc/mtab is a
proper symlink.
systemd will warn you during boot if /usr is on a different
file system than /. While in systemd itself very little will
break if /usr is on a separate partition many of its
dependencies very likely will break sooner or later in one
form or another. For example udev rules tend to refer to
binaries in /usr, binaries that link to libraries in /usr or
binaries that refer to data files in /usr. Since these
breakages are not always directly visible systemd will warn
about this, since this kind of file system setup is not really
supported anymore by the basic set of Linux OS components.
For more information on this issue consult
http://freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
To run systemd under valgrind, compile with VALGRIND defined
(e.g. ./configure CPPFLAGS='... -DVALGRIND=1'). Otherwise,
false positives will be triggered by code which violates
some rules but is actually safe.
ENGINEERING AND CONSULTING SERVICES:
ProFUSION <http://profusion.mobi> offers professional
engineering and consulting services for systemd for embedded
and other use. Please contact Gustavo Barbieri
<barbieri@profusion.mobi> for more information.
Disclaimer: This notice is not a recommendation or official
endorsement. However, ProFUSION's upstream work has been very
beneficial for the systemd project.