feat(radarbox): Implement rbfeeder_fixcputemp

Use LD_PRELOAD hook to workaround radarbox cpu temperature segfault issue.
Allow container to run on userspace podman where sysfs volume is impossible.

Signed-off-by: Jiaxun Yang <[email protected]>

Dockerfile

@@ -200,8 +200,21 @@ RUN set -x && \
     # mlat-client: simple test
     /usr/local/share/radarbox-mlat-client/venv/bin/python3 -c 'import mlat.client'
 
+FROM debian:bullseye as rbfeeder_fixcputemp
+SHELL ["/bin/bash", "-o", "pipefail", "-c"]
+ADD rbfeeder_fixcputemp ./
+RUN set -x && \
+    apt-get update && \
+    apt-get install -y --no-install-suggests --no-install-recommends \
+        build-essential
+ARG TARGETARCH
+RUN if [ $TARGETARCH != "arm" ]; then \
+        apt-get install -y crossbuild-essential-armhf \
+    ; fi
+RUN make CC=arm-linux-gnueabihf-gcc
+
 # THTTPD
-FROM alpine:3.13.2 AS thttpd
+FROM alpine:3.19.1 AS thttpd
 
 ENV THTTPD_VERSION=2.29
 
@@ -244,6 +257,7 @@ COPY --from=confd /opt/confd/bin/confd /copy_root/opt/confd/bin/
 COPY --from=radarbox /usr/bin/rbfeeder /copy_root/usr/bin/rbfeeder_armhf
 COPY --from=radarbox /usr/bin/dump1090-rb /copy_root/usr/bin/dump1090-rbs
 COPY --from=radarbox /usr/local/share/radarbox-mlat-client /copy_root/usr/local/share/radarbox-mlat-client
+COPY --from=rbfeeder_fixcputemp ./librbfeeder_fixcputemp.so /copy_root/usr/lib/arm-linux-gnueabihf/librbfeeder_fixcputemp.so
 ADD build /copy_root/build
 
 FROM debian:bullseye-slim as serve

build/rbfeeder_wrapper.sh

@@ -5,9 +5,10 @@
 
 # attempt to run natively
 if /usr/bin/rbfeeder_armhf --no-start --version >/dev/null 2>&1; then
+    export LD_PRELOAD=/usr/lib/arm-linux-gnueabihf/librbfeeder_fixcputemp.so
     /usr/bin/rbfeeder_armhf "$@"
 elif qemu-arm-static /usr/bin/rbfeeder_armhf --no-start --version >/dev/null 2>&1; then
-    qemu-arm-static /usr/bin/rbfeeder_armhf "$@"
+    qemu-arm-static -E LD_PRELOAD=/usr/lib/arm-linux-gnueabihf/librbfeeder_fixcputemp.so /usr/bin/rbfeeder_armhf "$@"
 else
     for i in {1..5}; do
         echo "FATAL: Could not run rbfeeder natively or via qemu!" | mawk -W interactive '{printf "%c[34m[radarbox-feeder]%c[0m %s\n", 27, 27, $0}'

rbfeeder_fixcputemp/.gitignore

@@ -0,0 +1,2 @@
+*.o
+*.so

rbfeeder_fixcputemp/Makefile

@@ -0,0 +1,11 @@
+CFLAGS := $(CFLAGS) -fPIC -Wall
+
+TARGET = librbfeeder_fixcputemp
+
+all: $(TARGET).so
+
+$(TARGET).so: $(TARGET).o
+	$(CC) $^ -shared -o $@
+
+clean:
+	rm *.so *.o

rbfeeder_fixcputemp/README.md

@@ -0,0 +1,24 @@
+# Fixup CPU Teampeature for RBFeeder
+
+This is a simple hook library for RBFeeder to fixup the CPU temperature measurement function on non-Raspberry Pi devices.
+
+## Implementation
+When running on a Raspberry Pi, the CPU temperature is read from the `/sys/class/thermal/thermal_zone0/temp` file. However this file does not exist on some other devices, and RBFeeder will crash because the file is not found.
+
+This library hooked `fopen` function to intercept the file open request for `/sys/class/thermal/thermal_zone0/temp` and return a fake file handle with a fixed temperature value if we are unable to open that file.
+
+## Usage
+1. Build the library by running `make` with cross compiler or on the target device.
+```
+$ make CC=arm-linux-gnueabihf-gcc
+```
+
+2. LD_PRELOAD the library when running RBFeeder.
+```
+$ LD_PRELOAD=./libfixcputemp.so ./rbfeeder
+```
+
+or if you are using qemu
+```
+$ qemu-arm -E LD_PRELOAD=./librbfeeder_fixcputemp.so ./rbfeeder
+```

rbfeeder_fixcputemp/librbfeeder_fixcputemp.c

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <dlfcn.h>
+
+#undef fopen
+
+ssize_t cputemp_read(void *cookie, char *buf, size_t size)
+{
+    const char temp[] = "0";
+    size_t len = sizeof(temp);
+    if (size < len)
+    {
+        return -1;
+    }
+    memcpy(buf, temp, len);
+    return len;
+}
+
+cookie_io_functions_t cputemp_funcs = {
+    .read = cputemp_read,
+};
+
+FILE *fopen(const char *path, const char *mode)
+{
+    FILE *orig_file = NULL;
+    static FILE *(*real_fopen)(const char *, const char *) = NULL;
+    if (real_fopen == NULL)
+    {
+        real_fopen = dlsym(RTLD_NEXT, "fopen");
+        if (real_fopen == NULL)
+        {
+            fprintf(stderr, "fixcputemp: Error in `dlsym`: %s\n", dlerror());
+            return NULL;
+        }
+    }
+
+    orig_file = real_fopen(path, mode);
+    if (orig_file)
+    {
+        return orig_file;
+    }
+
+    if (strcmp(path, "/sys/class/thermal/thermal_zone0/temp") == 0)
+    {
+        if (strcmp(mode, "r") != 0)
+        {
+            fprintf(stderr, "fixcputemp: fopen() called with mode other than 'r'\n");
+            return NULL;
+        }
+        return fopencookie(NULL, "r", cputemp_funcs);
+    }
+    return NULL;
+}