Support the use of device mapper for root filesystem mounts

This makes it possible to detect the physical block device that the root
filesystem uses even if Linux's device mapper is being used for
encrypted partitions or overlays or anything else.

src/mmc_linux.c

@@ -27,6 +27,7 @@
 #include <sys/wait.h>
 #include <sys/sysmacros.h>
 
+#include <dirent.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <stdbool.h>
@@ -235,20 +236,78 @@ int mmc_device_size(const char *mmc_path, off_t *end_offset)
     return *end_offset > 0 ? 0 : -1;
 }
 
+#define DEV_BLOCK_PATH_MAX 64
+#define DEV_ID_LENGTH 16 // "major:minor"
+
+static void dev_to_string(int dev, char *str)
+{
+    snprintf(str, DEV_ID_LENGTH, "%d:%d",  major(dev), minor(dev));
+}
+
+static int traverse_devices(const char *current, const char *goal, int depth_left)
+{
+    // Found?
+    if (strcmp(current, goal) == 0)
+        return 1;
+
+    // Traverse more?
+    if (depth_left <= 0)
+        return 0;
+    depth_left--;
+
+    // Check all device-mapper devices
+    int found_goal = 0;
+    char *slaves_path;
+    if (asprintf(&slaves_path, "/sys/dev/block/%s/slaves", current) < 0)
+        return 0;
+
+    struct dirent **namelist = NULL;
+    int n = scandir(slaves_path, &namelist, NULL, NULL);
+    for (int i = 0; i < n && !found_goal; i++) {
+        const char *name = namelist[i]->d_name;
+        if (name[0] == '.')
+            continue;
+
+        // The dev file contains the major:minor string
+        char *dev_path;
+        if (asprintf(&dev_path, "%s/%s/dev", slaves_path, name) < 0)
+            return 0;
+
+        char next[DEV_ID_LENGTH];
+        int rc = readsysfs(dev_path, next, sizeof(next));
+        if (rc > 0)
+            found_goal = traverse_devices(next, goal, depth_left);
+
+        free(dev_path);
+    }
+
+    free(slaves_path);
+    if (namelist) {
+        for (int i = 0; i < n; i++)
+            free(namelist[i]);
+        free(namelist);
+    }
+    return found_goal;
+}
+
 int mmc_is_path_on_device(const char *file_path, const char *device_path)
 {
+    char starting_device[DEV_ID_LENGTH];
+    char goal_device[DEV_ID_LENGTH];
+
     // Stat both paths.
-    struct stat file_st;
-    if (stat(file_path, &file_st) < 0)
+    struct stat sb;
+    if (stat(file_path, &sb) < 0)
         return -1;
+    dev_to_string(sb.st_dev, starting_device);
 
-    struct stat device_st;
-    if (stat(device_path, &device_st) < 0)
+    if (stat(device_path, &sb) < 0)
         return -1;
+    dev_to_string(sb.st_rdev, goal_device);
 
-    // Check that the device's major/minor are the same
-    // as the file's containing device's major/minor
-    return device_st.st_rdev == file_st.st_dev ? 1 : 0;
+    // Traverse through device-mapper mappings to see if we can get from the
+    // starting file_path's containing device to the block device of interest.
+    return traverse_devices(starting_device, goal_device, 3);
 }
 
 int mmc_is_path_at_device_offset(const char *file_path, off_t block_offset)

tests/210_new_require_path.test

@@ -0,0 +1,33 @@
+#!/bin/sh
+
+#
+# Tests that the "require-path-on-device" feature works. This allows one to
+# update firmware images based on where the filesystem is mounted.
+#
+
+. "$(cd "$(dirname "$0")" && pwd)/common.sh"
+
+$HAS_MOUNT_SHIM || exit 77
+
+cat >$CONFIG <<EOF
+task test.correct {
+    require-path-on-device("/", "/dev/rootdisk0p1")
+    on-init { info("correct") }
+}
+task test.fail {
+    on-init { error("something else!") }
+}
+EOF
+cat >$WORK/expected_output.txt <<EOF
+fwup: correct
+EOF
+
+# Create the firmware file the normal way
+$FWUP_CREATE -c -f $CONFIG -o $FWFILE
+
+# Use the mount shim instead of the write shim
+LD_PRELOAD="$MOUNT_LD_PRELOAD" DYLD_INSERT_LIBRARIES="$MOUNT_DYLD_INSERT_LIBRARIES" $FWUP_APPLY -a -q -d $IMGFILE -i $FWFILE -t test > $WORK/actual_output.txt
+diff -w $WORK/expected_output.txt $WORK/actual_output.txt
+
+# Check that the verify logic works on this file
+$FWUP_VERIFY -V -i $FWFILE

tests/211_new_require_path_dm.test

@@ -0,0 +1,46 @@
+#!/bin/sh
+
+#
+# Tests that the "require-path-on-device" feature can traverse through
+# device mapper mounts.
+#
+
+. "$(cd "$(dirname "$0")" && pwd)/common.sh"
+
+$HAS_MOUNT_SHIM || exit 77
+
+if [ "$HOST_OS" != "Linux" ]; then
+    echo "Skipping since device mapper logic only on Linux-specific fwup code."
+    exit 77
+fi
+
+cat >$CONFIG <<EOF
+task test.correct {
+    require-path-on-device("/boot", "/dev/mmcblk0p2")
+    on-init { info("correct") }
+}
+task test.fail {
+    on-init { error("something else!") }
+}
+EOF
+cat >$WORK/expected_output.txt <<EOF
+fwup: correct
+EOF
+
+# Create the firmware file the normal way
+$FWUP_CREATE -c -f $CONFIG -o $FWFILE
+
+# Set up some fake /sys/dev/block directories similar to device mapper
+mkdir -p $WORK/sys/dev/block/254:0/slaves/mmcblk0p1 # Fake entry to test scanning
+mkdir -p $WORK/sys/dev/block/254:0/slaves/mmcblk0p2
+mkdir -p $WORK/sys/dev/block/254:0/slaves/mmcblk0p3 # Fake entry to test scanning
+echo "1:1" > $WORK/sys/dev/block/254:0/slaves/mmcblk0p1/dev
+echo "179:2" > $WORK/sys/dev/block/254:0/slaves/mmcblk0p2/dev
+echo "1:1" > $WORK/sys/dev/block/254:0/slaves/mmcblk0p3/dev
+
+# Use the mount shim instead of the write shim
+LD_PRELOAD="$MOUNT_LD_PRELOAD" DYLD_INSERT_LIBRARIES="$MOUNT_DYLD_INSERT_LIBRARIES" $FWUP_APPLY -a -q -d $IMGFILE -i $FWFILE -t test > $WORK/actual_output.txt
+diff -w $WORK/expected_output.txt $WORK/actual_output.txt
+
+# Check that the verify logic works on this file
+$FWUP_VERIFY -V -i $FWFILE

tests/Makefile.am

@@ -209,6 +209,8 @@ TESTS = 001_simple_fw.test \
 	206_mbr_ebr_missing_partition.test \
 	207_mbr_ebr_overlapping_records.test \
 	208_mbr_ebr_overlapping_parts.test \
-	209_reboot_param.test
+	209_reboot_param.test \
+	210_new_require_path.test \
+	211_new_require_path_dm.test
 
 EXTRA_DIST = $(TESTS) common.sh 1K.bin 1K-corrupt.bin 150K.bin

tests/common.sh

@@ -140,7 +140,19 @@ else
     export HAS_WRITE_SHIM=false
 fi
 
-WORK=$TESTS_DIR/work-$(basename "$0")
+# The mount simulator only runs only runs on a subset of
+# platforms. Let autoconf figure out which ones.
+MOUNT_SHIM="$TESTS_DIR/fixture/.libs/libmount_shim.$SO_EXT"
+if [ -e "$MOUNT_SHIM" ]; then
+    export HAS_MOUNT_SHIM=true
+    export MOUNT_LD_PRELOAD="$MOUNT_SHIM"
+    export MOUNT_DYLD_INSERT_LIBRARIES="$MOUNT_SHIM"
+else
+    export HAS_MOUNT_SHIM=false
+fi
+
+# Export WORK for the shims to use if needed
+export WORK=$TESTS_DIR/work-$(basename "$0")
 RESULTS=$WORK/results
 
 CONFIG=$WORK/fwup.conf

tests/fixture/.gitignore

@@ -2,3 +2,4 @@
 /verify-syscalls
 /.libs
 /libwrite_shim*
+/libmount_shim*

tests/fixture/Makefile.am

@@ -11,11 +11,15 @@ verify_syscalls_SOURCES=verify-syscalls.c
 endif
 
 if HAS_WRITE_SHIM
-check_LTLIBRARIES = libwrite_shim.la
+check_LTLIBRARIES = libwrite_shim.la libmount_shim.la
 libwrite_shim_la_SOURCES = write_shim.c
 
 # The "-rpath /nowhere" is the trick to getting libtool to create a shared library for
 # "check" LTLIBRARIES.
 libwrite_shim_la_LDFLAGS = ${AM_LDFLAGS} -ldl -dynamiclib -avoid-version -shared -rpath /nowhere
 libwrite_shim_la_CFLAGS = ${AM_CFLAGS}
+
+libmount_shim_la_SOURCES = mount_shim.c
+libmount_shim_la_LDFLAGS = ${AM_LDFLAGS} -ldl -dynamiclib -avoid-version -shared -rpath /nowhere
+libmount_shim_la_CFLAGS = ${AM_CFLAGS} -D_FILE_OFFSET_BITS=64
 endif