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udev-cache: stop race between sysconf and cache generation 

The validity of the udev cache is determined by the sysconf
file (/etc/udev/cache.data). Currently, there is a substantial delay
between sysconf generation in /etc/init.d/udev and cache generation in
/etc/init.d/udev-cache. If a hotplug event arrives in the middle of
this, then the sysconf will be out of date with respect to the cache.

The solution is two-pronged. First, we minimize the race window by
regenerating the sysconf immediately before the cache, in
/etc/init.d/udev-cache. This allows us to kill the race entirely by
stopping the udev event queue while the sysconf and cache are being
generated.

(From OE-Core rev: 107e7fa2b2cc2e06addb83518c03b3ab769fed6f)

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Richard Tollerton 2014-12-08 16:44:33 -06:00 committed by Richard Purdie
parent a957ff1dc4
commit 24a159e169
1 changed files with 18 additions and 0 deletions
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18
meta/recipes-core/udev/udev/udev-cache
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@ -19,8 +19,22 @@ export TZ=/etc/localtime
DEVCACHE_TMP="/dev/shm/udev-cache-tmp.tar"
SYSCONF_CACHED="/etc/udev/cache.data"
SYSCONF_TMP="/dev/shm/udev.cache"
# A list of files which are used as a criteria to judge whether the udev cache could be reused.
CMP_FILE_LIST="/proc/version /proc/cmdline /proc/devices /proc/atags"
[ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
readfiles () {
READDATA=""
for filename in $@; do
if [ -r $filename ]; then
while read line; do
READDATA="$READDATA$line"
done < $filename
fi
done
}
if [ "$ROOTFS_READ_ONLY" = "yes" ]; then
[ "$VERBOSE" != "no" ] && echo "udev-cache: read-only rootfs, skip generating udev-cache"
exit 0
@ -28,11 +42,15 @@ fi
if [ "$DEVCACHE" != "" -a -e "$SYSCONF_TMP" ]; then
echo "Populating dev cache"
udevadm control --stop-exec-queue
readfiles $CMP_FILE_LIST
echo "$READDATA" > "$SYSCONF_TMP"
find /dev -xdev \( -type b -o -type c -o -type l \) | cut -c 2- \
| xargs tar cf "${DEVCACHE_TMP}" -T-
gzip < "${DEVCACHE_TMP}" > "$DEVCACHE"
rm -f "${DEVCACHE_TMP}"
mv "$SYSCONF_TMP" "$SYSCONF_CACHED"
udevadm control --start-exec-queue
fi
exit 0