安卓10添加修改serial串口的服务

首先添加一个可执行程序源码，在安卓源码目录下system/core/下增加drmservice/drmservice.cpp文件，

#include <stdlib.h>
#include <android-base/logging.h>
#include <fcntl.h>
#include <android-base/properties.h>
#include <cutils/properties.h>

#define SERIAL_NUMBER_DATE "/data/cloudserial"

using android::base::GetProperty;

static int unix_read(int  fd, void*  buff, int  len) {
    int  ret;
    do { ret = read(fd, buff, len); } while (ret < 0 && errno == EINTR);
    return ret;
}

static int sys_read(const char*  filename, char* buff, size_t  buffsize) {
    int  len = 0;
    int  fd  = open(filename, O_RDONLY);
    if (fd >= 0) {
        len = unix_read(fd, buff, buffsize-1);
        close(fd);
    }
    buff[len > 0 ? len : 0] = 0;
    return len;
}

int main( int argc, char *argv[] )
{

    LOG(INFO) << "drmservice start" << argc;
    LOG(INFO) << "argv = " << argv[0];

    char custom_serial[128];
    int len = 0;
    constexpr const char* UNSET = "";

    len = sys_read("/data/cloudserial", custom_serial, sizeof(custom_serial));
    if ( len > 0 ) {
        property_set("ro.serialno", custom_serial);
    } else {
        len = sys_read("/sys/hardware_info/serial_no_info", custom_serial, sizeof(custom_serial));
        if (len > 0) {
            property_set("ro.serialno", custom_serial);
        } else {
            std::string value2 = GetProperty("ro.boot.serialno", UNSET);
            if (value2 != UNSET) {
                strcpy(custom_serial,value2.c_str());
                    property_set("ro.serialno", custom_serial);
            }
        }
    }
    return 0;
}
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然后添加编译脚本：system/core/drmservice/Android.bp文件，具体内容如下

cc_binary {
    name: "drmservice",
    srcs: ["drmservice.cpp"],
    cflags: [
        "-Wall",
        "-Wextra",
        "-Werror",
    ],
    shared_libs: [
        "libbase",
        "libutils",
        "libcutils",
        "liblog",
    ],
}
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添加完之后再在对应平台的编译脚本中添加如下两句话，将drmservice添加进去

PRODUCT_PACKAGES += \
    drmservice
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比如我这里是如下路径

diff --git a/android/device/softwinner/ceres-c3/ceres_c3.mk b/android/device/softwinner/ceres-c3/ceres_c3.mk
index 499430b8ce..f96e5b0f2c 100644
--- a/android/device/softwinner/ceres-c3/ceres_c3.mk
+++ b/android/device/softwinner/ceres-c3/ceres_c3.mk
@@ -183,6 +183,9 @@ PRODUCT_PACKAGES +=\
     libmc_watchdog \
     libmc_sound

+PRODUCT_PACKAGES += \
+    drmservice
+
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然后将drmservice服务添加到对应的init.rc中，比如我这里是如下路径

diff --git a/android/device/softwinner/ceres-common/init.sun50iw10p1.rc b/android/device/softwinner/ceres-common/init.sun50iw10p1.rc
index a0e5ec7c7c..bd9fc35cf8 100644
--- a/android/device/softwinner/ceres-common/init.sun50iw10p1.rc
+++ b/android/device/softwinner/ceres-common/init.sun50iw10p1.rc
@@ -83,6 +83,8 @@ on boot
     chown -R system:system /oem/media
     chmod 0644 /oem/media/bootanimation.zip

+    start drmservice
+
 on post-fs-data
     # create file for audio dump data
     mkdir /data/vendor/hardware/audio_d 0777 audio audio
@@ -128,3 +130,9 @@ service mciputils /system/bin/mciputils
        group root
        oneshot
        disabled
+
+service drmservice /system/bin/drmservice
+        class main
+       user root
+        group root
+        oneshot
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一个服务就算添加成功了，接着就是增加服务执行的selinux权限了。这是我这里

diff --git a/android/system/sepolicy/prebuilts/api/26.0/private/drmservice.te b/android/system/sepolicy/prebuilts/api/26.0/private/drmservice.te
new file mode 100644
index 0000000000..271613749c
--- /dev/null
+++ b/android/system/sepolicy/prebuilts/api/26.0/private/drmservice.te
@@ -0,0 +1,2 @@
+typeattribute drmservice coredomain;
+typeattribute drmservice domain_deprecated;
diff --git a/android/system/sepolicy/prebuilts/api/26.0/public/drmservice.te b/android/system/sepolicy/prebuilts/api/26.0/public/drmservice.te
new file mode 100644
index 0000000000..881a1dbb9f
--- /dev/null
+++ b/android/system/sepolicy/prebuilts/api/26.0/public/drmservice.te
@@ -0,0 +1,2 @@
+type drmservice, domain;
+type drmservice_exec, exec_type, file_type;
diff --git a/android/system/sepolicy/prebuilts/api/27.0/private/drmservice.te b/android/system/sepolicy/prebuilts/api/27.0/private/drmservice.te
new file mode 100644
index 0000000000..271613749c
--- /dev/null
+++ b/android/system/sepolicy/prebuilts/api/27.0/private/drmservice.te
@@ -0,0 +1,2 @@
+typeattribute drmservice coredomain;
+typeattribute drmservice domain_deprecated;
diff --git a/android/system/sepolicy/prebuilts/api/27.0/public/drmservice.te b/android/system/sepolicy/prebuilts/api/27.0/public/drmservice.te
new file mode 100644
index 0000000000..881a1dbb9f
--- /dev/null
+++ b/android/system/sepolicy/prebuilts/api/27.0/public/drmservice.te
@@ -0,0 +1,2 @@
+type drmservice, domain;
+type drmservice_exec, exec_type, file_type;
diff --git a/android/system/sepolicy/prebuilts/api/28.0/private/drmservice.te b/android/system/sepolicy/prebuilts/api/28.0/private/drmservice.te
new file mode 100644
index 0000000000..20172c8105
--- /dev/null
+++ b/android/system/sepolicy/prebuilts/api/28.0/private/drmservice.te
@@ -0,0 +1 @@
+typeattribute drmservice coredomain;
diff --git a/android/system/sepolicy/prebuilts/api/28.0/public/drmservice.te b/android/system/sepolicy/prebuilts/api/28.0/public/drmservice.te
new file mode 100644
index 0000000000..881a1dbb9f
--- /dev/null
+++ b/android/system/sepolicy/prebuilts/api/28.0/public/drmservice.te
@@ -0,0 +1,2 @@
+type drmservice, domain;
+type drmservice_exec, exec_type, file_type;
diff --git a/android/system/sepolicy/prebuilts/api/29.0/private/coredomain.te b/android/system/sepolicy/prebuilts/api/29.0/private/coredomain.te
index d66a66c07c..622316dde3 100644
--- a/android/system/sepolicy/prebuilts/api/29.0/private/coredomain.te
+++ b/android/system/sepolicy/prebuilts/api/29.0/private/coredomain.te
@@ -105,7 +105,7 @@ full_treble_only(`
     -vold
     -system_server
     -priv_app
-  } sysfs:file no_rw_file_perms;
+  } sysfs:file { append create link unlink relabelfrom rename setattr write ioctl lock };

   # /dev
   neverallow {
diff --git a/android/system/sepolicy/prebuilts/api/29.0/private/drmservice.te b/android/system/sepolicy/prebuilts/api/29.0/private/drmservice.te
new file mode 100644
index 0000000000..1c54ea3802
--- /dev/null
+++ b/android/system/sepolicy/prebuilts/api/29.0/private/drmservice.te
@@ -0,0 +1,14 @@
+type drmservice, domain, coredomain;
+type drmservice_exec, system_file_type, exec_type, file_type;
+
+init_daemon_domain(drmservice)
+
+allow drmservice unlabeled:dir search;
+allow drmservice drmservice:capability { dac_override dac_read_search };
+allow drmservice serialno_prop:file { getattr open read  };
+allow drmservice sysfs:file { open read };
+allow drmservice property_socket:sock_file { write };
+allow drmservice init:unix_stream_socket { connectto };
+allow drmservice system_data_file:file { read open };
+allow drmservice system_prop:property_service { set };
+allow drmservice serialno_prop:property_service { set };
diff --git a/android/system/sepolicy/prebuilts/api/29.0/private/file_contexts b/android/system/sepolicy/prebuilts/api/29.0/private/file_contexts
index 530bd45fac..cd6d87e491 100644
--- a/android/system/sepolicy/prebuilts/api/29.0/private/file_contexts
+++ b/android/system/sepolicy/prebuilts/api/29.0/private/file_contexts
@@ -328,6 +328,9 @@
 /system/bin/notify_traceur\.sh       u:object_r:notify_traceur_exec:s0
 /system/bin/migrate_legacy_obb_data\.sh u:object_r:migrate_legacy_obb_data_exec:s0

+#zxy
+/system/bin/drmservice           u:object_r:drmservice_exec:s0
+
 #############################
 # Vendor files
 #
diff --git a/android/system/sepolicy/prebuilts/api/29.0/public/domain.te b/android/system/sepolicy/prebuilts/api/29.0/public/domain.te
index 9e6873d08f..fce2fa7816 100644
--- a/android/system/sepolicy/prebuilts/api/29.0/public/domain.te
+++ b/android/system/sepolicy/prebuilts/api/29.0/public/domain.te
@@ -559,7 +559,7 @@ neverallow {
   -vendor_init
   -zygote
   -priv_app
-} serialno_prop:file r_file_perms;
+} serialno_prop:file { ioctl lock };

 # Do not allow reading the last boot timestamp from system properties
 neverallow { domain -init -system_server -dumpstate -priv_app} firstboot_prop:file r_file_perms;
diff --git a/android/system/sepolicy/private/coredomain.te b/android/system/sepolicy/private/coredomain.te
index d66a66c07c..622316dde3 100644
--- a/android/system/sepolicy/private/coredomain.te
+++ b/android/system/sepolicy/private/coredomain.te
@@ -105,7 +105,7 @@ full_treble_only(`
     -vold
     -system_server
     -priv_app
-  } sysfs:file no_rw_file_perms;
+  } sysfs:file { append create link unlink relabelfrom rename setattr write ioctl lock };

   # /dev
   neverallow {
diff --git a/android/system/sepolicy/private/drmservice.te b/android/system/sepolicy/private/drmservice.te
new file mode 100644
index 0000000000..1c54ea3802
--- /dev/null
+++ b/android/system/sepolicy/private/drmservice.te
@@ -0,0 +1,14 @@
+type drmservice, domain, coredomain;
+type drmservice_exec, system_file_type, exec_type, file_type;
+
+init_daemon_domain(drmservice)
+
+allow drmservice unlabeled:dir search;
+allow drmservice drmservice:capability { dac_override dac_read_search };
+allow drmservice serialno_prop:file { getattr open read  };
+allow drmservice sysfs:file { open read };
+allow drmservice property_socket:sock_file { write };
+allow drmservice init:unix_stream_socket { connectto };
+allow drmservice system_data_file:file { read open };
+allow drmservice system_prop:property_service { set };
+allow drmservice serialno_prop:property_service { set };
diff --git a/android/system/sepolicy/private/file_contexts b/android/system/sepolicy/private/file_contexts
index 530bd45fac..cd6d87e491 100644
--- a/android/system/sepolicy/private/file_contexts
+++ b/android/system/sepolicy/private/file_contexts
@@ -328,6 +328,9 @@
 /system/bin/notify_traceur\.sh       u:object_r:notify_traceur_exec:s0
 /system/bin/migrate_legacy_obb_data\.sh u:object_r:migrate_legacy_obb_data_exec:s0

+#zxy
+/system/bin/drmservice           u:object_r:drmservice_exec:s0
+
 #############################
 # Vendor files
 #
diff --git a/android/system/sepolicy/public/domain.te b/android/system/sepolicy/public/domain.te
index 9e6873d08f..fce2fa7816 100644
--- a/android/system/sepolicy/public/domain.te
+++ b/android/system/sepolicy/public/domain.te
@@ -559,7 +559,7 @@ neverallow {
   -vendor_init
   -zygote
   -priv_app
-} serialno_prop:file r_file_perms;
+} serialno_prop:file { ioctl lock };

 # Do not allow reading the last boot timestamp from system properties
 neverallow { domain -init -system_server -dumpstate -priv_app} firstboot_prop:file r_file_perms;
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