Allow the use of a custom Android DT directory

On platforms that use ACPI instead of Device Tree (DT), such as
Ranchu x86/x86_64, /proc/device-tree/firmware/android/ does not
exist. As a result, Android O is unable to mount /system, etc.
at the first stage of init:

 init: First stage mount skipped (missing/incompatible fstab in
 device tree)

Those platforms may create another directory that mimics the layout
of the standard DT directory in procfs, and store early mount
configuration there. E.g., Ranchu x86/x86_64 creates one in sysfs
using information encoded in the ACPI tables:

 https://android-review.googlesource.com/442472
 https://android-review.googlesource.com/443432
 https://android-review.googlesource.com/442393
 https://android-review.googlesource.com/442395

Therefore, instead of hardcoding the Android DT path, load it from
the kernel command line using a new Android-specific property key
("androidboot.android_dt_dir"). If no such property exists, fall
back to the standard procfs path (so no change is needed for DT-
aware platforms).

Note that init/ and fs_mgr/ each have their own copy of the Android
DT path, because they do not share any global state. A future CL
should remove the duplication by refactoring.

With this CL as well as the above ones, the said warning is gone,
but early mount fails. That is a separate bug, though, and will be
addressed by another CL.

Test: Boot patched sdk_phone_x86-userdebug system image with patched
      Goldfish 3.18 x86 kernel in patched Android Emulator, verify
      the "init: First stage mount skipped" warning no longer shows
      in dmesg.

Change-Id: Ib6df577319503ec1ca778de2b5458cc72ce07415
Signed-off-by: Yu Ning <yu.ning@intel.com>

fs_mgr/fs_mgr_boot_config.cpp

@@ -23,19 +23,11 @@
 
 #include "fs_mgr_priv.h"
 
-// Tries to get the boot config value in properties, kernel cmdline and
-// device tree (in that order).  returns 'true' if successfully found, 'false'
-// otherwise
-bool fs_mgr_get_boot_config(const std::string& key, std::string* out_val) {
+// Tries to get the given boot config value from kernel cmdline.
+// Returns true if successfully found, false otherwise.
+bool fs_mgr_get_boot_config_from_kernel_cmdline(const std::string& key, std::string* out_val) {
     FS_MGR_CHECK(out_val != nullptr);
 
-    // first check if we have "ro.boot" property already
-    *out_val = android::base::GetProperty("ro.boot." + key, "");
-    if (!out_val->empty()) {
-        return true;
-    }
-
-    // fallback to kernel cmdline, properties may not be ready yet
     std::string cmdline;
     std::string cmdline_key("androidboot." + key);
     if (android::base::ReadFileToString("/proc/cmdline", &cmdline)) {
@@ -50,9 +42,29 @@ bool fs_mgr_get_boot_config(const std::string& key, std::string* out_val) {
         }
     }
 
+    return false;
+}
+
+// Tries to get the boot config value in properties, kernel cmdline and
+// device tree (in that order).  returns 'true' if successfully found, 'false'
+// otherwise
+bool fs_mgr_get_boot_config(const std::string& key, std::string* out_val) {
+    FS_MGR_CHECK(out_val != nullptr);
+
+    // first check if we have "ro.boot" property already
+    *out_val = android::base::GetProperty("ro.boot." + key, "");
+    if (!out_val->empty()) {
+        return true;
+    }
+
+    // fallback to kernel cmdline, properties may not be ready yet
+    if (fs_mgr_get_boot_config_from_kernel_cmdline(key, out_val)) {
+        return true;
+    }
+
     // lastly, check the device tree
     if (is_dt_compatible()) {
-        std::string file_name = kAndroidDtDir + "/" + key;
+        std::string file_name = get_android_dt_dir() + "/" + key;
         if (android::base::ReadFileToString(file_name, out_val)) {
             if (!out_val->empty()) {
                 out_val->pop_back();  // Trims the trailing '\0' out.

fs_mgr/fs_mgr_fstab.cpp

@@ -29,6 +29,8 @@
 
 #include "fs_mgr_priv.h"
 
+const std::string kDefaultAndroidDtDir("/proc/device-tree/firmware/android");
+
 struct fs_mgr_flag_values {
     char *key_loc;
     char *verity_loc;
@@ -313,9 +315,26 @@ static int parse_flags(char *flags, struct flag_list *fl,
     return f;
 }
 
+static std::string init_android_dt_dir() {
+    std::string android_dt_dir;
+    // The platform may specify a custom Android DT path in kernel cmdline
+    if (!fs_mgr_get_boot_config_from_kernel_cmdline("android_dt_dir", &android_dt_dir)) {
+        // Fall back to the standard procfs-based path
+        android_dt_dir = kDefaultAndroidDtDir;
+    }
+    return android_dt_dir;
+}
+
+// FIXME: The same logic is duplicated in system/core/init/
+const std::string& get_android_dt_dir() {
+    // Set once and saves time for subsequent calls to this function
+    static const std::string kAndroidDtDir = init_android_dt_dir();
+    return kAndroidDtDir;
+}
+
 static bool is_dt_fstab_compatible() {
     std::string dt_value;
-    std::string file_name = kAndroidDtDir + "/fstab/compatible";
+    std::string file_name = get_android_dt_dir() + "/fstab/compatible";
     if (read_dt_file(file_name, &dt_value)) {
         if (dt_value == "android,fstab") {
             return true;
@@ -331,7 +350,7 @@ static std::string read_fstab_from_dt() {
         return fstab;
     }
 
-    std::string fstabdir_name = kAndroidDtDir + "/fstab";
+    std::string fstabdir_name = get_android_dt_dir() + "/fstab";
     std::unique_ptr<DIR, int (*)(DIR*)> fstabdir(opendir(fstabdir_name.c_str()), closedir);
     if (!fstabdir) return fstab;
 
@@ -394,7 +413,7 @@ static std::string read_fstab_from_dt() {
 }
 
 bool is_dt_compatible() {
-    std::string file_name = kAndroidDtDir + "/compatible";
+    std::string file_name = get_android_dt_dir() + "/compatible";
     std::string dt_value;
     if (read_dt_file(file_name, &dt_value)) {
         if (dt_value == "android,firmware") {

fs_mgr/fs_mgr_priv.h

@@ -119,6 +119,7 @@ bool fs_mgr_wait_for_file(const std::string& filename,
                           const std::chrono::milliseconds relative_timeout);
 bool fs_mgr_update_for_slotselect(struct fstab *fstab);
 bool fs_mgr_is_device_unlocked();
+const std::string& get_android_dt_dir();
 bool is_dt_compatible();
 bool is_device_secure();
 int load_verity_state(struct fstab_rec* fstab, int* mode);

fs_mgr/fs_mgr_priv_boot_config.h

@@ -20,8 +20,7 @@
 #include <sys/cdefs.h>
 #include <string>
 
-const std::string kAndroidDtDir("/proc/device-tree/firmware/android");
-
+bool fs_mgr_get_boot_config_from_kernel_cmdline(const std::string& key, std::string* out_val);
 bool fs_mgr_get_boot_config(const std::string& key, std::string* out_val);
 
 #endif /* __CORE_FS_MGR_PRIV_BOOTCONFIG_H */

init/init.cpp

@@ -513,7 +513,7 @@ static void process_kernel_dt() {
         return;
     }
 
-    std::unique_ptr<DIR, int (*)(DIR*)> dir(opendir(kAndroidDtDir.c_str()), closedir);
+    std::unique_ptr<DIR, int (*)(DIR*)> dir(opendir(get_android_dt_dir().c_str()), closedir);
     if (!dir) return;
 
     std::string dt_file;
@@ -523,7 +523,7 @@ static void process_kernel_dt() {
             continue;
         }
 
-        std::string file_name = kAndroidDtDir + dp->d_name;
+        std::string file_name = get_android_dt_dir() + dp->d_name;
 
         android::base::ReadFileToString(file_name, &dt_file);
         std::replace(dt_file.begin(), dt_file.end(), ',', '.');

init/util.cpp

@@ -53,6 +53,8 @@ using namespace std::literals::string_literals;
 namespace android {
 namespace init {
 
+const std::string kDefaultAndroidDtDir("/proc/device-tree/firmware/android/");
+
 // DecodeUid() - decodes and returns the given string, which can be either the
 // numeric or name representation, into the integer uid or gid. Returns
 // UINT_MAX on error.
@@ -374,10 +376,31 @@ void panic() {
     DoReboot(ANDROID_RB_RESTART2, "reboot", "bootloader", false);
 }
 
-// Reads the content of device tree file under kAndroidDtDir directory.
+static std::string init_android_dt_dir() {
+    // Use the standard procfs-based path by default
+    std::string android_dt_dir = kDefaultAndroidDtDir;
+    // The platform may specify a custom Android DT path in kernel cmdline
+    import_kernel_cmdline(false,
+                          [&](const std::string& key, const std::string& value, bool in_qemu) {
+                              if (key == "androidboot.android_dt_dir") {
+                                  android_dt_dir = value;
+                              }
+                          });
+    LOG(INFO) << "Using Android DT directory " << android_dt_dir;
+    return android_dt_dir;
+}
+
+// FIXME: The same logic is duplicated in system/core/fs_mgr/
+const std::string& get_android_dt_dir() {
+    // Set once and saves time for subsequent calls to this function
+    static const std::string kAndroidDtDir = init_android_dt_dir();
+    return kAndroidDtDir;
+}
+
+// Reads the content of device tree file under the platform's Android DT directory.
 // Returns true if the read is success, false otherwise.
 bool read_android_dt_file(const std::string& sub_path, std::string* dt_content) {
-    const std::string file_name = kAndroidDtDir + sub_path;
+    const std::string file_name = get_android_dt_dir() + sub_path;
     if (android::base::ReadFileToString(file_name, dt_content)) {
         if (!dt_content->empty()) {
             dt_content->pop_back();  // Trims the trailing '\0' out.

init/util.h

@@ -30,8 +30,6 @@
 
 #define COLDBOOT_DONE "/dev/.coldboot_done"
 
-const std::string kAndroidDtDir("/proc/device-tree/firmware/android/");
-
 using android::base::boot_clock;
 using namespace std::chrono_literals;
 
@@ -57,7 +55,10 @@ bool expand_props(const std::string& src, std::string* dst);
 
 void panic() __attribute__((__noreturn__));
 
-// Reads or compares the content of device tree file under kAndroidDtDir directory.
+// Returns the platform's Android DT directory as specified in the kernel cmdline.
+// If the platform does not configure a custom DT path, returns the standard one (based in procfs).
+const std::string& get_android_dt_dir();
+// Reads or compares the content of device tree file under the platform's Android DT directory.
 bool read_android_dt_file(const std::string& sub_path, std::string* dt_content);
 bool is_android_dt_value_expected(const std::string& sub_path, const std::string& expected_content);