[PATCH v2 00/12] udev-cache related changes

[PATCH v2 00/12] udev-cache related changes

[Richard Tollerton]

This is v2 of the changes submitted by Ben Shelton on August 4. I've reworked the
patches quite a bit, larger changes include:

- All non-udev-cache-related patches have been omitted. I'll submit those
  separately.
- Use `find` to build `tar` filelist. This eliminates the need for GNU- and
  busybox-specific tar options.
- No new settings have been added to udev-cache.default in order to preserve
  compatibility with older overrides of udev-cache.default. Note, this means a
  lot of new settings are duplicated between initscripts.
- System config is now generated immediately before the tarball is generated,
  and is manipulated at the file level instead of the shell variable level.
- Internal/corporate commit message fields stripped.
- Spurious whitespace changes should all be fixed.

There is one requested fix I'm pushing back on: Copying both $CMP_FILE_LIST and
/dev to tmpfs in a single operation to minimize race conditions. For a variety
of reasons, I abandoned trying to make this work in a single command. Instead
it's done in two: grabbing the system configuration (i.e reading /proc files and
udev rules) is done first, then /dev is archived as an uncompressed tarball.
Notably, using tar instead of cp means that I can use `find -xdev` and `find
-type` to eliminate a lot of other complexity. I think this approach will wind
up being faster than the straight-up copy approach, although I have not made any
attempt to confirm that.

The following changes since commit 47d1fc9f5c38f3d092937c47bd4c2f45adaa7fe6:

  qemu: fix Darwin cross-compilation (2014-08-18 20:43:24 +0100)

are available in the git repository at:

  git://github.com/rtollert/openembedded-core dev/rtollert/udev-cache-7
  https://github.com/rtollert/openembedded-core/tree/dev/rtollert/udev-cache-7

Richard Tollerton (12):
  udev-cache: Update cache tarball atomically
  udev-cache: Compress the cache
  udev-cache: choose a more descriptive cache filename
  busybox: enable `tar -m`
  udev-cache: strip timestamps on extract
  udev-cache: omit sockets and filesystems mounted under /dev
  udev-cache: Don't ignore error messages from cache extract
  udev-cache: parametrize sysconf file paths
  udev-cache: get system config immediately before cache
  udev-cache: invalidate on rules.d changes
  udev-cache: Update cache asynchronously
  udev-cache: refactor; improve verbosity and error handling

 meta/recipes-core/busybox/busybox/defconfig    |  2 +-
 meta/recipes-core/udev/udev/init               | 53 ++++++++++++--------------
 meta/recipes-core/udev/udev/udev-cache         | 42 ++++++++++++++++++--
 meta/recipes-core/udev/udev/udev-cache.default |  2 +-
 4 files changed, 64 insertions(+), 35 deletions(-)

-- 
2.0.4

[PATCH v2 01/12] udev-cache: Update cache tarball atomically

[Richard Tollerton]

Overwriting the tarball in-place could cause a partial write, if the
system stops at an inopportune time. This is mitigated by first writing
to a temporary file, then moving that file on top of the final location.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Ben Shelton <ben.shelton@ni.com>
Acked-by: Gratian Crisan <gratian.crisan@ni.com>
---
 meta/recipes-core/udev/udev/udev-cache | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index db5a513..c08cef2 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -16,6 +16,7 @@ export TZ=/etc/localtime
 [ -d /sys/class ] || exit 1
 
 [ -f /etc/default/rcS ] && . /etc/default/rcS
+DEVCACHE_TMP="/dev/shm/udev-cache-tmp.tar"
 [ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
 
 if [ "$ROOTFS_READ_ONLY" = "yes" ]; then
@@ -25,7 +26,8 @@ fi
 
 if [ "$DEVCACHE" != "" -a -e /dev/shm/udev.cache ]; then
 	echo "Populating dev cache"
-	(cd /; tar cf "$DEVCACHE" dev)
+	(cd /; tar cf "${DEVCACHE_TMP}" dev)
+	mv -f "${DEVCACHE_TMP}" "$DEVCACHE"
 	mv /dev/shm/udev.cache /etc/udev/cache.data
 fi
 
-- 
2.0.4

[PATCH v2 02/12] udev-cache: Compress the cache

[Richard Tollerton]

$DEVCACHE is observed to be 100k uncompressed; compressing it reduces
its size to ~5k. But compress it outside of `tar` so that archival
operation takes as little time as possible, to minimize the risk of
devices being created/removed during execution.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/udev-cache         | 3 ++-
 meta/recipes-core/udev/udev/udev-cache.default | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index c08cef2..ec07f50 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -27,7 +27,8 @@ fi
 if [ "$DEVCACHE" != "" -a -e /dev/shm/udev.cache ]; then
 	echo "Populating dev cache"
 	(cd /; tar cf "${DEVCACHE_TMP}" dev)
-	mv -f "${DEVCACHE_TMP}" "$DEVCACHE"
+	gzip < "${DEVCACHE_TMP}" > "$DEVCACHE"
+	rm -f "${DEVCACHE_TMP}"
 	mv /dev/shm/udev.cache /etc/udev/cache.data
 fi
 
diff --git a/meta/recipes-core/udev/udev/udev-cache.default b/meta/recipes-core/udev/udev/udev-cache.default
index 2093336..909ec87 100644
--- a/meta/recipes-core/udev/udev/udev-cache.default
+++ b/meta/recipes-core/udev/udev/udev-cache.default
@@ -1,5 +1,5 @@
 # Default for /etc/init.d/udev
 
 # Comment this out to disable device cache
-DEVCACHE="/etc/dev.tar"
+DEVCACHE="/etc/dev.tar.gz"
 PROBE_PLATFORM_BUS="yes"
-- 
2.0.4

[PATCH v2 03/12] udev-cache: choose a more descriptive cache filename

[Richard Tollerton]

"/etc/dev.tar.gz" doesn't adequately imply that udev-cache maintains it.
Instead, call it "/etc/udev-cache.tar.gz".

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Ben Shelton <ben.shelton@ni.com>
Acked-by: Gratian Crisan <gratian.crisan@ni.com>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
---
 meta/recipes-core/udev/udev/udev-cache.default | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/recipes-core/udev/udev/udev-cache.default b/meta/recipes-core/udev/udev/udev-cache.default
index 909ec87..a3b7326 100644
--- a/meta/recipes-core/udev/udev/udev-cache.default
+++ b/meta/recipes-core/udev/udev/udev-cache.default
@@ -1,5 +1,5 @@
 # Default for /etc/init.d/udev
 
 # Comment this out to disable device cache
-DEVCACHE="/etc/dev.tar.gz"
+DEVCACHE="/etc/udev-cache.tar.gz"
 PROBE_PLATFORM_BUS="yes"
-- 
2.0.4

[PATCH v2 04/12] busybox: enable `tar -m`

[Richard Tollerton]

CONFIG_FEATURE_TAR_NOPRESERVE_TIME=y is needed for the commit
"udev-cache: strip timestamps on extract". Enabling this flag increases
the size of busybox by 0 bytes on x86.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/busybox/busybox/defconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/recipes-core/busybox/busybox/defconfig b/meta/recipes-core/busybox/busybox/defconfig
index 35f1026..8394067 100644
--- a/meta/recipes-core/busybox/busybox/defconfig
+++ b/meta/recipes-core/busybox/busybox/defconfig
@@ -159,7 +159,7 @@ CONFIG_FEATURE_TAR_GNU_EXTENSIONS=y
 # CONFIG_FEATURE_TAR_LONG_OPTIONS is not set
 # CONFIG_FEATURE_TAR_TO_COMMAND is not set
 # CONFIG_FEATURE_TAR_UNAME_GNAME is not set
-# CONFIG_FEATURE_TAR_NOPRESERVE_TIME is not set
+CONFIG_FEATURE_TAR_NOPRESERVE_TIME=y
 # CONFIG_FEATURE_TAR_SELINUX is not set
 # CONFIG_UNCOMPRESS is not set
 # CONFIG_UNLZMA is not set
-- 
2.0.4

[PATCH v2 05/12] udev-cache: strip timestamps on extract

[Richard Tollerton]

Under normal udev operation, device nodes are obviously timestamped
based on the system time at current boot. However, when using
udev-cache, they are timestamped from a previous boot.

The existence of machines lacking RTCs makes this more than a cosmetic
issue: if the current time is set further on in the boot, so that the
system time is still 1970 by the time the cache is extracted, tar will
print a timestamp warning for every extracted file (potentially hundreds
of them).

To fix, use -m on extract.

If using busybox `tar`, this commit requires
CONFIG_FEATURE_TAR_NOPRESERVE_TIME=y.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/init | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/recipes-core/udev/udev/init b/meta/recipes-core/udev/udev/init
index f2c84d5..4a6df6e 100644
--- a/meta/recipes-core/udev/udev/init
+++ b/meta/recipes-core/udev/udev/init
@@ -69,7 +69,7 @@ case "$1" in
 		    readfiles /etc/udev/cache.data
 		    OLDDATA="$READDATA"
 		    if [ "$OLDDATA" = "$NEWDATA" ]; then
-                            (cd /; tar xf $DEVCACHE > /dev/null 2>&1)
+                            (cd /; tar xmf $DEVCACHE > /dev/null 2>&1)
                             not_first_boot=1
                             [ "$VERBOSE" != "no" ] && echo "udev: using cache file $DEVCACHE"
                             [ -e /dev/shm/udev.cache ] && rm -f /dev/shm/udev.cache
-- 
2.0.4

[PATCH v2 06/12] udev-cache: omit sockets and filesystems mounted under /dev

[Richard Tollerton]

Archiving sockets causes tar to report an error and return a nonzero
exit status. Archiving a mounted filesystem is harmless, but may greatly
bloat the size of the cache tarball, and wastes time on boot.

To fix these issues, use `find` to only include the files we want, which
are the file types that udev will create (block/char devices and
symlinks) that are on the same filesystem as /dev.

While we're at it, remove a subshell by archiving /dev as an absolute
path. However, `tar` will complain about stripping the leading slash on
stderr. To inhibit this, `cut` out the leading slash.

An alternative solution is to use `tar --exclude`, but that is modestly
more brittle, since we'd need to explicitly list every socket and
filesystem to exclude. Note that `tar --one-file-system` is
GNU-specific, and tar implementations generally have nothing equivalent
to `find -type`.

If using busybox `find`, this change requires CONFIG_FEATURE_FIND_TYPE=y
and CONFIG_FEATURE_FIND_XDEV=y. If using busybox `tar`, this change
requires CONFIG_FEATURE_TAR_FROM=y.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/udev-cache | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index ec07f50..aaf1ddd 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -26,7 +26,8 @@ fi
 
 if [ "$DEVCACHE" != "" -a -e /dev/shm/udev.cache ]; then
 	echo "Populating dev cache"
-	(cd /; tar cf "${DEVCACHE_TMP}" dev)
+	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 /dev/shm/udev.cache /etc/udev/cache.data
-- 
2.0.4

[PATCH v2 07/12] udev-cache: Don't ignore error messages from cache extract

[Richard Tollerton]

Previous changes should obviate all known spurious errors coming out of
tar. Since real extraction failures can and will occur, stop redirecting
stdout/stderr to /dev/null.

Take this opportunity to also remove an unnecessary subshell.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/init | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/recipes-core/udev/udev/init b/meta/recipes-core/udev/udev/init
index 4a6df6e..1d073c2 100644
--- a/meta/recipes-core/udev/udev/init
+++ b/meta/recipes-core/udev/udev/init
@@ -69,7 +69,7 @@ case "$1" in
 		    readfiles /etc/udev/cache.data
 		    OLDDATA="$READDATA"
 		    if [ "$OLDDATA" = "$NEWDATA" ]; then
-                            (cd /; tar xmf $DEVCACHE > /dev/null 2>&1)
+                            tar xmf $DEVCACHE -C / -m
                             not_first_boot=1
                             [ "$VERBOSE" != "no" ] && echo "udev: using cache file $DEVCACHE"
                             [ -e /dev/shm/udev.cache ] && rm -f /dev/shm/udev.cache
-- 
2.0.4

[PATCH v2 08/12] udev-cache: parametrize sysconf file paths

[Richard Tollerton]

The udev-cache facility uses files that represent system states, to
ensure that the cache tarball is valid to apply. These paths were
hardcoded in several places; collect them into SYSCONF_CACHED and
SYSCONF_TMP.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/init       | 10 ++++++----
 meta/recipes-core/udev/udev/udev-cache |  6 ++++--
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/meta/recipes-core/udev/udev/init b/meta/recipes-core/udev/udev/init
index 1d073c2..7ffa4a6 100644
--- a/meta/recipes-core/udev/udev/init
+++ b/meta/recipes-core/udev/udev/init
@@ -14,6 +14,8 @@ export TZ=/etc/localtime
 [ -d /sys/class ] || exit 1
 [ -r /proc/mounts ] || exit 1
 [ -x @UDEVD@ ] || exit 1
+SYSCONF_CACHED="/etc/udev/cache.data"
+SYSCONF_TMP="/dev/shm/udev.cache"
 [ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
 [ -f /etc/udev/udev.conf ] && . /etc/udev/udev.conf
 [ -f /etc/default/rcS ] && . /etc/default/rcS
@@ -66,13 +68,13 @@ case "$1" in
             if [ -e $DEVCACHE ]; then
 		    readfiles $CMP_FILE_LIST
 		    NEWDATA="$READDATA"
-		    readfiles /etc/udev/cache.data
+		    readfiles "$SYSCONF_CACHED"
 		    OLDDATA="$READDATA"
 		    if [ "$OLDDATA" = "$NEWDATA" ]; then
                             tar xmf $DEVCACHE -C / -m
                             not_first_boot=1
                             [ "$VERBOSE" != "no" ] && echo "udev: using cache file $DEVCACHE"
-                            [ -e /dev/shm/udev.cache ] && rm -f /dev/shm/udev.cache
+                            [ -e $SYSCONF_TMP ] && rm -f "$SYSCONF_TMP"
                     else
 			    # Output detailed reason why the cached /dev is not used
 			    if [ "$VERBOSE" != "no" ]; then
@@ -81,14 +83,14 @@ case "$1" in
 				    echo "udev: olddata: $OLDDATA"
 				    echo "udev: newdata: $NEWDATA"
 			    fi
-			    echo "$NEWDATA" > /dev/shm/udev.cache
+			    echo "$NEWDATA" > "$SYSCONF_TMP"
                     fi
 	    else
 		    if [ "$ROOTFS_READ_ONLY" != "yes" ]; then
 			    # If rootfs is not read-only, it's possible that a new udev cache would be generated;
 			    # otherwise, we do not bother to read files.
 			    readfiles $CMP_FILE_LIST
-			    echo "$READDATA" > /dev/shm/udev.cache
+			    echo "$READDATA" > "$SYSCONF_TMP"
 		    fi
             fi
     fi
diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index aaf1ddd..497d257 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -17,6 +17,8 @@ export TZ=/etc/localtime
 
 [ -f /etc/default/rcS ] && . /etc/default/rcS
 DEVCACHE_TMP="/dev/shm/udev-cache-tmp.tar"
+SYSCONF_CACHED="/etc/udev/cache.data"
+SYSCONF_TMP="/dev/shm/udev.cache"
 [ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
 
 if [ "$ROOTFS_READ_ONLY" = "yes" ]; then
@@ -24,13 +26,13 @@ if [ "$ROOTFS_READ_ONLY" = "yes" ]; then
     exit 0
 fi
 
-if [ "$DEVCACHE" != "" -a -e /dev/shm/udev.cache ]; then
+if [ "$DEVCACHE" != "" -a -e "$SYSCONF_TMP" ]; then
 	echo "Populating dev cache"
 	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 /dev/shm/udev.cache /etc/udev/cache.data
+	mv "$SYSCONF_TMP" "$SYSCONF_CACHED"
 fi
 
 exit 0
-- 
2.0.4

[PATCH v2 09/12] udev-cache: get system config immediately before cache

[Richard Tollerton]

The system device configuration -- /proc/devices, /proc/cmdline, etc. --
and the contents of /dev must be stored as simultaneously as possible.
Otherwise, hotplug events could be processed between the time we get the
system config and the time we archive /dev, and the udev cache may be
incorrect.

To solve this, update the cached system configuration inside the
udev-cache initscript, not the udev initscript. Also, run it before
archiving /dev, because it should execute nearly instantaneously.

We still need to compute the system configuration inside the udev
initscript, to detect if it changed, so refactor it into a new function
sysconf_cmd(). This also allows administrators to modify it for
machine-specific requirements.

Evaluating the system configuration requires a shell function
readfiles() defined in the udev initscript. The only salient differences
between readfiles() and just using `cat` directly are a) readfiles()
skips files without error if they don't exist, which is necessary
because /proc/atags is in CMP_FILE_LIST but does not exist on all
targets; and b) input lines are concatenated into an output shell
variable with newlines stripped. (a) can be eliminated by not including
/proc/atags in CMP_FILE_LIST if it doesn't exist. (b) is O(n^2) anyway,
and makes $NEWDATA, $OLDDATA etc. very hard to read, and we don't need
to strip newlines anyway. So make sysconf_cmd() use `cat` and remove
readfiles().

Instead of storing system configuration in shell variables ($NEWDATA,
$OLDDATA), store them directly in files: redirect to $SYSCONF_TMP
instead of storing in $NEWDATA; read from $SYSCONF_CACHED directly
instead of reading it into $OLDDATA. This turns comparing $NEWDATA vs.
$OLDDATA into a call to `cmp`. However, busybox lacks `cmp -q`, so
instead, redirect cmp's output to /dev/null.

$OLDDATA and $NEWDATA go away. This obviates the most of error message
printed when the udev cache can't be used, but it probably wasn't of
much help, because $OLDDATA and $NEWDATA are so large that they would
have scrolled off the screen anyway. Beyond that, this error is so
important that it should probably be printed regardless of the setting
of VERBOSE. So leave the "udev: cache not used" log message and remove
everything else.

Because the udev-cache initscript evaluates the system configuration
itself, it makes no sense to signal it to run by storing the system
configuration in a file. Instead, signal udev-cache execution by
touching a file, $DEVCACHE_REGEN.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/init       | 44 +++++++++++++---------------------
 meta/recipes-core/udev/udev/udev-cache | 17 +++++++++++--
 2 files changed, 31 insertions(+), 30 deletions(-)

diff --git a/meta/recipes-core/udev/udev/init b/meta/recipes-core/udev/udev/init
index 7ffa4a6..10cbf56 100644
--- a/meta/recipes-core/udev/udev/init
+++ b/meta/recipes-core/udev/udev/init
@@ -16,21 +16,20 @@ export TZ=/etc/localtime
 [ -x @UDEVD@ ] || exit 1
 SYSCONF_CACHED="/etc/udev/cache.data"
 SYSCONF_TMP="/dev/shm/udev.cache"
+DEVCACHE_REGEN="/dev/shm/udev-regen" # create to request cache regen
+
+# List of files whose contents will be included in cached system state.
+CMP_FILE_LIST="/proc/version /proc/cmdline /proc/devices"
+[ -f /proc/atags ] && CMP_FILE_LIST="$CMP_FILE_LIST /proc/atags"
+
+# Command to compute system configuration.
+sysconf_cmd () {
+	cat -- $CMP_FILE_LIST
+}
 [ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
 [ -f /etc/udev/udev.conf ] && . /etc/udev/udev.conf
 [ -f /etc/default/rcS ] && . /etc/default/rcS
 
-readfiles () {
-   READDATA=""
-   for filename in $@; do
-	   if [ -r $filename ]; then
-		   while read line; do
-			   READDATA="$READDATA$line"
-		   done < $filename
-	   fi
-   done
-}
-
 kill_udevd () {
     pid=`pidof -x udevd`
     [ -n "$pid" ] && kill $pid
@@ -62,35 +61,24 @@ case "$1" in
     mkdir -p /var/volatile/tmp
 
     # Cache handling.
-    # 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"
     if [ "$DEVCACHE" != "" ]; then
             if [ -e $DEVCACHE ]; then
-		    readfiles $CMP_FILE_LIST
-		    NEWDATA="$READDATA"
-		    readfiles "$SYSCONF_CACHED"
-		    OLDDATA="$READDATA"
-		    if [ "$OLDDATA" = "$NEWDATA" ]; then
+		    sysconf_cmd > $SYSCONF_TMP
+		    if cmp $SYSCONF_CACHED $SYSCONF_TMP >/dev/null; then
                             tar xmf $DEVCACHE -C / -m
                             not_first_boot=1
                             [ "$VERBOSE" != "no" ] && echo "udev: using cache file $DEVCACHE"
-                            [ -e $SYSCONF_TMP ] && rm -f "$SYSCONF_TMP"
+                            [ -e "$DEVCACHE_REGEN" ] && rm -f "$DEVCACHE_REGEN"
                     else
 			    # Output detailed reason why the cached /dev is not used
-			    if [ "$VERBOSE" != "no" ]; then
-				    echo "udev: udev cache not used"
-				    echo "udev: we use $CMP_FILE_LIST as criteria to judge whether the cache /dev could be resued"
-				    echo "udev: olddata: $OLDDATA"
-				    echo "udev: newdata: $NEWDATA"
-			    fi
-			    echo "$NEWDATA" > "$SYSCONF_TMP"
+			    echo "udev: cache not used"
+			    touch "$DEVCACHE_REGEN"
                     fi
 	    else
 		    if [ "$ROOTFS_READ_ONLY" != "yes" ]; then
 			    # If rootfs is not read-only, it's possible that a new udev cache would be generated;
 			    # otherwise, we do not bother to read files.
-			    readfiles $CMP_FILE_LIST
-			    echo "$READDATA" > "$SYSCONF_TMP"
+			    touch "$DEVCACHE_REGEN"
 		    fi
             fi
     fi
diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index 497d257..5a1bc78 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -19,6 +19,16 @@ export TZ=/etc/localtime
 DEVCACHE_TMP="/dev/shm/udev-cache-tmp.tar"
 SYSCONF_CACHED="/etc/udev/cache.data"
 SYSCONF_TMP="/dev/shm/udev.cache"
+DEVCACHE_REGEN="/dev/shm/udev-regen" # create to request cache regen
+
+# List of files whose contents will be included in cached system state.
+CMP_FILE_LIST="/proc/version /proc/cmdline /proc/devices"
+[ -f /proc/atags ] && CMP_FILE_LIST="$CMP_FILE_LIST /proc/atags"
+
+# Command to compute system configuration.
+sysconf_cmd () {
+	cat -- $CMP_FILE_LIST
+}
 [ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
 
 if [ "$ROOTFS_READ_ONLY" = "yes" ]; then
@@ -26,13 +36,16 @@ if [ "$ROOTFS_READ_ONLY" = "yes" ]; then
     exit 0
 fi
 
-if [ "$DEVCACHE" != "" -a -e "$SYSCONF_TMP" ]; then
+if [ "$DEVCACHE" != "" -a -e "$DEVCACHE_REGEN" ]; then
 	echo "Populating dev cache"
+	# Run sysconf_cmd before `tar`, not after, so that as little time as
+	# possible elapses between creating $SYSCONF_CACHED and $DEVCACHE.
+	sysconf_cmd > "$SYSCONF_CACHED"
 	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"
+	rm -f "$DEVCACHE_REGEN"
 fi
 
 exit 0
-- 
2.0.4

Re: [PATCH v2 09/12] udev-cache: get system config immediately before cache

[Richard Purdie]

On Fri, 2014-08-22 at 16:30 -0500, Richard Tollerton wrote:
> The system device configuration -- /proc/devices, /proc/cmdline, etc. --
> and the contents of /dev must be stored as simultaneously as possible.
> Otherwise, hotplug events could be processed between the time we get the
> system config and the time we archive /dev, and the udev cache may be
> incorrect.
> 
> To solve this, update the cached system configuration inside the
> udev-cache initscript, not the udev initscript. Also, run it before
> archiving /dev, because it should execute nearly instantaneously.
> 
> We still need to compute the system configuration inside the udev
> initscript, to detect if it changed, so refactor it into a new function
> sysconf_cmd(). This also allows administrators to modify it for
> machine-specific requirements.
> 
> Evaluating the system configuration requires a shell function
> readfiles() defined in the udev initscript. The only salient differences
> between readfiles() and just using `cat` directly are a) readfiles()
> skips files without error if they don't exist, which is necessary
> because /proc/atags is in CMP_FILE_LIST but does not exist on all
> targets; and b) input lines are concatenated into an output shell
> variable with newlines stripped. (a) can be eliminated by not including
> /proc/atags in CMP_FILE_LIST if it doesn't exist. (b) is O(n^2) anyway,
> and makes $NEWDATA, $OLDDATA etc. very hard to read, and we don't need
> to strip newlines anyway. So make sysconf_cmd() use `cat` and remove
> readfiles().

The reason this was done was actually c) avoid having to execute cat as
a new process.

> Instead of storing system configuration in shell variables ($NEWDATA,
> $OLDDATA), store them directly in files: redirect to $SYSCONF_TMP
> instead of storing in $NEWDATA; read from $SYSCONF_CACHED directly
> instead of reading it into $OLDDATA. This turns comparing $NEWDATA vs.
> $OLDDATA into a call to `cmp`. However, busybox lacks `cmp -q`, so
> instead, redirect cmp's output to /dev/null.

The above reason c) is also why we don't use cmp. It turned out to be
faster to read into a variable than fork/exec cmp.

Cheers,

Richard

Re: [PATCH v2 09/12] udev-cache: get system config immediately before cache

[Richard Tollerton]

Richard Purdie <richard.purdie@linuxfoundation.org> writes:

> The above reason c) is also why we don't use cmp. It turned out to be
> faster to read into a variable than fork/exec cmp.

You appear to be wrong: cat+cmp is 27-41% faster than readfiles. In
fact, testing cat alone (without cmp) shows that `cat` to tmpfs file is
2x-3x as fast as readfiles.

These figures reproduce on both a Xilinx Zynq Cortex-A9 and my Xeon dev
machine; the former running busybox sh, the latter running bash.

See below for test script.

---

#!/bin/busybox sh

files="/proc/version /proc/cmdline /proc/devices"
runs=100

readfiles () {
   READDATA=""
   for filename in $@; do
	   if [ -r $filename ]; then
		   while read line; do
			   READDATA="$READDATA$line"
		   done < $filename
	   fi
   done
}

dotest_cat_inner () {
	cat $@
}

dotest_cat () {
	cat $@ > /tmp/a.txt
	cat $@ > /tmp/b.txt
	cmp /tmp/a.txt /tmp/b.txt
}

dotest_readfiles_inner () {
	readfiles $@
	echo "$READDATA"
}

dotest_readfiles () {
	readfiles $@
	NEWDATA="$READDATA"
	readfiles $@
	OLDDATA="$OLDDATA"
	[ "$OLDDATA" = "$NEWDATA" ]
}

timetest () {
	cmd=$1
	i=$2
	shift 2
	while [ "$i" -gt 0 ]; do
		$cmd $@ >/dev/null
		i=$(( i-1 ))
	done
}

case $1 in
cat) timetest dotest_cat $runs $files ;;
readfiles) timetest dotest_readfiles $runs $files ;;
inner_cat) timetest dotest_cat_inner $runs $files ;;
inner_readfiles) timetest dotest_readfiles_inner $runs $files ;;
*) 
	printf 'cat:\n'
	time $0 cat

	printf '\nreadfiles:\n'
	time $0 readfiles

	printf '\ncat_inner:\n'
	time $0 inner_cat

	printf '\nreadfiles_inner:\n'
	time $0 inner_readfiles
	;;
esac


> Cheers,
>
> Richard
>

-- 
Richard Tollerton <rich.tollerton@ni.com>

[PATCH v2 10/12] udev-cache: invalidate on rules.d changes

[Richard Tollerton]

Presently, the cache is not regenerated if udev rules are modified,
which may cause the cache to preserve an old configuration. To fix,
include the size, mtime, and filename of all udev rules in the system
configuration.

This change requires `stat`. If busybox supplies stat,
CONFIG_FEATURE_STAT_FORMAT must be enabled.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/init       | 5 +++++
 meta/recipes-core/udev/udev/udev-cache | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/meta/recipes-core/udev/udev/init b/meta/recipes-core/udev/udev/init
index 10cbf56..c44dc2d 100644
--- a/meta/recipes-core/udev/udev/init
+++ b/meta/recipes-core/udev/udev/init
@@ -22,9 +22,14 @@ DEVCACHE_REGEN="/dev/shm/udev-regen" # create to request cache regen
 CMP_FILE_LIST="/proc/version /proc/cmdline /proc/devices"
 [ -f /proc/atags ] && CMP_FILE_LIST="$CMP_FILE_LIST /proc/atags"
 
+# List of files whose metadata (size/mtime/name) will be included in cached
+# system state.
+META_FILE_LIST="lib/udev/rules.d/* etc/udev/rules.d/*"
+
 # Command to compute system configuration.
 sysconf_cmd () {
 	cat -- $CMP_FILE_LIST
+	stat -L -c '%s %Y %n' -- $META_FILE_LIST | awk -F/ '{print $1 " " $NF;}'
 }
 [ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
 [ -f /etc/udev/udev.conf ] && . /etc/udev/udev.conf
diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index 5a1bc78..c499676 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -25,9 +25,14 @@ DEVCACHE_REGEN="/dev/shm/udev-regen" # create to request cache regen
 CMP_FILE_LIST="/proc/version /proc/cmdline /proc/devices"
 [ -f /proc/atags ] && CMP_FILE_LIST="$CMP_FILE_LIST /proc/atags"
 
+# List of files whose metadata (size/mtime/name) will be included in cached
+# system state.
+META_FILE_LIST="lib/udev/rules.d/* etc/udev/rules.d/*"
+
 # Command to compute system configuration.
 sysconf_cmd () {
 	cat -- $CMP_FILE_LIST
+	stat -L -c '%s %Y %n' -- $META_FILE_LIST | awk -F/ '{print $1 " " $NF;}'
 }
 [ -f /etc/default/udev-cache ] && . /etc/default/udev-cache
 
-- 
2.0.4

[PATCH v2 11/12] udev-cache: Update cache asynchronously

[Richard Tollerton]

Don't hold up the boot while the cache is being updated.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Ben Shelton <ben.shelton@ni.com>
Acked-by: Gratian Crisan <gratian.crisan@ni.com>
---
 meta/recipes-core/udev/udev/udev-cache | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index c499676..baeb125 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -43,14 +43,17 @@ fi
 
 if [ "$DEVCACHE" != "" -a -e "$DEVCACHE_REGEN" ]; then
 	echo "Populating dev cache"
-	# Run sysconf_cmd before `tar`, not after, so that as little time as
-	# possible elapses between creating $SYSCONF_CACHED and $DEVCACHE.
-	sysconf_cmd > "$SYSCONF_CACHED"
-	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}"
-	rm -f "$DEVCACHE_REGEN"
+	(
+		# Run sysconf_cmd before `tar`, not after, so that as little
+		# time as possible elapses between creating $SYSCONF_CACHED and
+		# $DEVCACHE.
+		sysconf_cmd > "$SYSCONF_CACHED"
+		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}"
+		rm -f "$DEVCACHE_REGEN"
+	) &
 fi
 
 exit 0
-- 
2.0.4

[PATCH v2 12/12] udev-cache: refactor; improve verbosity and error handling

[Richard Tollerton]

Most of /etc/init.d/udev-cache is in a conditional block which can be
replaced by a `[ ... ] || exit 0` to reduce nesting. This also
provides an opportunity to improve handling of VERBOSE a bit.

Previously, errors encountered during find, tar, etc. were ignored,
which could mask some problems, or cause invalid cache files to get
created. To solve: abort the update process (and report an error) if any
command in the process fails; and write the system configuration to
$SYSCONF_TMP first -- only update $SYSCONF_CACHED when we are certain
that the cache tarball was successfully created.

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
---
 meta/recipes-core/udev/udev/udev-cache | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/meta/recipes-core/udev/udev/udev-cache b/meta/recipes-core/udev/udev/udev-cache
index baeb125..dc97198 100644
--- a/meta/recipes-core/udev/udev/udev-cache
+++ b/meta/recipes-core/udev/udev/udev-cache
@@ -41,19 +41,26 @@ if [ "$ROOTFS_READ_ONLY" = "yes" ]; then
     exit 0
 fi
 
-if [ "$DEVCACHE" != "" -a -e "$DEVCACHE_REGEN" ]; then
-	echo "Populating dev cache"
-	(
-		# Run sysconf_cmd before `tar`, not after, so that as little
-		# time as possible elapses between creating $SYSCONF_CACHED and
-		# $DEVCACHE.
-		sysconf_cmd > "$SYSCONF_CACHED"
-		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}"
-		rm -f "$DEVCACHE_REGEN"
-	) &
+[ "$DEVCACHE" != "" ] || exit 0
+[ "${VERBOSE}" == "no" ] || echo -n "udev-cache: checking for ${DEVCACHE_REGEN}... "
+if ! [ -e "$DEVCACHE_REGEN" ]; then
+	[ "${VERBOSE}" == "no" ] || echo "not found."
+	exit 0
 fi
+[ "${VERBOSE}" == "no" ] || echo "found; building cache."
+
+(
+	# Run sysconf_cmd before `tar`, not after, so that as little time as
+	# possible elapses between creating $SYSCONF_CACHED and $DEVCACHE.
+	if ! { sysconf_cmd > "$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}" > "$DEVCACHE" \
+		&& mv "$SYSCONF_TMP" "$SYSCONF_CACHED" \
+		&& rm -f "$DEVCACHE_REGEN" "${DEVCACHE_TMP}"; }
+	then
+		echo "udev-cache: update failed!"
+	fi
+) &
 
 exit 0
-- 
2.0.4