udev-cache: replace readfiles() with cmp

Currently, udev-cache system configurations are compared as shell string
variables, read into memory with the readfiles() function. This is more
complex, and significantly (27-41%) slower, than comparing them using
`cmp`. (Performance was verified on both Cortex-A9 and Intel Nehalem
systems.)

So just use cmp. This requires a few other small changes:

exclude /proc/atags from CMP_FILE_LIST if it doesn't exist to avoid
errors in `cat` and `cmp`.

`cmp -q` doesn't exist in busybox, so instead, redirect output to
/dev/null.

(From OE-Core rev: e8ea6a29ed3ab9892a3bc7ee8249f10688c0af29)

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 3 insertions, 14 deletions

diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index a1410f5579..e0e1c39488 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -21,20 +21,10 @@ 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"
+CMP_FILE_LIST="/proc/version /proc/cmdline /proc/devices"
+[ -f /proc/atags ] && CMP_FILE_LIST="$CMP_FILE_LIST /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
     [ "$VERBOSE" != "no" ] && echo "udev-cache: read-only rootfs, skip generating udev-cache"
     exit 0
@@ -43,8 +33,7 @@ fi
 if [ "$DEVCACHE" != "" -a -e "$SYSCONF_TMP" ]; then
         echo "Populating dev cache"
         udevadm control --stop-exec-queue
-        readfiles $CMP_FILE_LIST
-        echo "$READDATA" > "$SYSCONF_TMP"
+        cat -- $CMP_FILE_LIST > "$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"