os-helpers: fs: replace wait4file w/ inotifywait

Previously, scripts that required a file that is created asynchronously, such as the by-state links created by a udev rule, would busy loop until the file existed using wait4file(), part of os-helpers-fs. This is time consuming and inefficient, as the minimum wait time adds latency to the following operations. Instead, use inotifywait to receive an event from the kernel when the relevant file or path is modified to prevent unnecessary resource usage and busy waiting. Change-type: patch Signed-off-by: Joseph Kogut <[email protected]>
balena-os · Mar 24, 2023 · 1c7244e · 1c7244e
1 parent ead4a8f
commit 1c7244e
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Showing 6 changed files with 20 additions and 33 deletions.
diff --git a/meta-balena-common/recipes-core/initrdscripts/files/fsuuidsinit b/meta-balena-common/recipes-core/initrdscripts/files/fsuuidsinit
@@ -30,12 +30,11 @@ fsuuidsinit_enabled() {
         return 1
     fi
 
-    # Wait for balena by-state symlinks to come up
-    # We only wait for resin-rootA here as we use it right away
-    # but we in fact assume the other symlinks are created as well
-    # wait4file does $2 loops of 100ms, therefore use 10 * roottimeout
     timeout=${bootparam_roottimeout:-5}
-    if ! wait4file "/dev/disk/by-state/resin-rootA" "$((timeout * 10))"; then
+    if ! ls /dev/disk/by-state/* \
+        && ! inotifywait -r /dev \
+                         --include 'disk/by-state/resin-+(boot|data|root[AB]|state)$' \
+                         --timeout "${timeout}"; then
         error "Timeout while waiting for resin-root partition to be detected"
         return 1
     fi

diff --git a/meta-balena-common/recipes-core/initrdscripts/files/machineid b/meta-balena-common/recipes-core/initrdscripts/files/machineid
@@ -13,10 +13,13 @@ machineid_enabled() {
 machineid_run() {
     # Mount the state partition - that's where we store the machine_id
     state_partition_path="$(get_state_path_from_label "resin-state")"
-    if ! wait4file "$state_partition_path" "300"; then
+    if [ ! -e "${state_partition_path}" ] \
+        && ! inotifywait -r /dev \
+                         --include "${state_partition_path#/dev/}" \
+                         --timeout 30; then
         error "Timeout while waiting for resin-state partition to be detected."
         error "Not able to mount resin-state, machine-id will not be persistent."
-	return
+        return
     fi
 
     info "Binding machine-id from ${state_partition_path}"

diff --git a/meta-balena-common/recipes-core/initrdscripts/files/resindataexpander b/meta-balena-common/recipes-core/initrdscripts/files/resindataexpander
@@ -28,8 +28,12 @@ resindataexpander_enabled() {
     datadev=$(lsblk "/dev/${datapartdev}" -d -n -o PKNAME)
     pttype=$(get_part_table_type "/dev/${datadev}")
 
-    if ! wait4file "$datapart" "300"; then
-        error "Timeout while waiting for data partition to be detected. Data partition expansion will not be tried."
+    if [ ! -e "${datapart}" ] \
+        && ! inotifywait -r /dev \
+                         --include "${datapart#/dev/}" \
+                         --timeout 30; then
+        error "Timeout while waiting for data partition to be detected." \
+            "Data partition expansion will not be tried."
         return 1
     fi
 

diff --git a/meta-balena-common/recipes-support/os-helpers/os-helpers.bb b/meta-balena-common/recipes-support/os-helpers/os-helpers.bb
@@ -4,7 +4,7 @@ LICENSE = "Apache-2.0"
 LIC_FILES_CHKSUM = "file://${BALENA_COREBASE}/COPYING.Apache-2.0;md5=89aea4e17d99a7cacdbeed46a0096b10"
 
 DEPENDS = "time-native"
-RDEPENDS:${PN}-fs = "e2fsprogs-tune2fs mtools parted bash util-linux-fdisk"
+RDEPENDS:${PN}-fs = "e2fsprogs-tune2fs mtools parted bash util-linux-fdisk inotify-tools"
 RDEPENDS:${PN}-fs:append = "${@bb.utils.contains('MACHINE_FEATURES','raid',' mdadm','',d)}"
 RDEPENDS:${PN}-tpm2 = "libtss2-tcti-device tpm2-tools"
 RDEPENDS:${PN}-config = "bash"

diff --git a/meta-balena-common/recipes-support/os-helpers/os-helpers/os-helpers-fs b/meta-balena-common/recipes-support/os-helpers/os-helpers/os-helpers-fs
@@ -16,26 +16,6 @@ if [ -f "/usr/libexec/os-helpers-logging" ]; then
 . /usr/libexec/os-helpers-logging
 fi
 
-# Wait for a file to appear with loop count limit.
-# Use-case example: wait for udev to create a filesystem symlink.
-# Arguments:
-#   1 - target path
-#   2 - number of loops (each loop sleeps for 100ms)
-wait4file() {
-	_lpath="$1"
-	_lloops="$2"
-
-	while [ ! -e "$_lpath" ]; do
-		if [ "$_lloops" -gt 0 ]; then
-			sleep 0.1
-			_lloops=$((_lloops-1))
-		else
-			return 1
-		fi
-	done
-	return 0
-}
-
 # Output the UUID for the specified block device.
 # Arguments:
 #   1 - Target block device

diff --git a/meta-balena-common/recipes-support/resin-mounts/resin-mounts/resin-partition-mounter b/meta-balena-common/recipes-support/resin-mounts/resin-mounts/resin-partition-mounter
@@ -20,8 +20,6 @@
 
 set -e
 
-TIMEOUT_LOOPS=300 # ~ 100ms/loop * 300loops = 30000ms = 30s
-
 #
 # Help message
 #
@@ -103,7 +101,10 @@ if [ ! -d "$target_mountpoint" ]; then
     echo "ERROR: Target mountpoint $target_mountpoint not found."
     exit 1
 fi
-if ! wait4file "$target_path" "$TIMEOUT_LOOPS"; then
+if [ ! -e "${target_path}" ] \
+    && ! inotifywait -r /dev \
+                     --include "${target_path#/dev/}" \
+                     --timeout 30; then
     echo "ERROR: Timeout while waiting for $target_path to come up."
     exit 1
 fi