init: Make 'write_file' return bool to match 'read_file'.

The mismatch of return values makes reasoning about the correctness of
CLs like https://android-review.googlesource.com/317923 quite hard.

Bug: 33941660
Test: Init builds, HiKey boots.
Change-Id: Ia4b8a9af420682997b154a594892740181980921

init/builtins.cpp

@@ -249,7 +249,7 @@ static int do_class_reset(const std::vector<std::string>& args) {
 }
 
 static int do_domainname(const std::vector<std::string>& args) {
-    return write_file("/proc/sys/kernel/domainname", args[1].c_str());
+    return write_file("/proc/sys/kernel/domainname", args[1].c_str()) ? 0 : 1;
 }
 
 static int do_enable(const std::vector<std::string>& args) {
@@ -277,7 +277,7 @@ static int do_export(const std::vector<std::string>& args) {
 }
 
 static int do_hostname(const std::vector<std::string>& args) {
-    return write_file("/proc/sys/kernel/hostname", args[1].c_str());
+    return write_file("/proc/sys/kernel/hostname", args[1].c_str()) ? 0 : 1;
 }
 
 static int do_ifup(const std::vector<std::string>& args) {
@@ -814,7 +814,7 @@ static int do_verity_update_state(const std::vector<std::string>& args) {
 static int do_write(const std::vector<std::string>& args) {
     const char* path = args[1].c_str();
     const char* value = args[2].c_str();
-    return write_file(path, value);
+    return write_file(path, value) ? 0 : 1;
 }
 
 static int do_copy(const std::vector<std::string>& args) {

init/init.cpp

@@ -542,7 +542,7 @@ static void selinux_initialize(bool in_kernel_domain) {
             }
         }
 
-        if (write_file("/sys/fs/selinux/checkreqprot", "0") == -1) {
+        if (!write_file("/sys/fs/selinux/checkreqprot", "0")) {
             security_failure();
         }
 

init/util.cpp

@@ -185,18 +185,18 @@ bool read_file(const char* path, std::string* content) {
     return okay;
 }
 
-int write_file(const char* path, const char* content) {
+bool write_file(const char* path, const char* content) {
     int fd = TEMP_FAILURE_RETRY(open(path, O_WRONLY|O_CREAT|O_NOFOLLOW|O_CLOEXEC, 0600));
     if (fd == -1) {
         PLOG(ERROR) << "write_file: Unable to open '" << path << "'";
-        return -1;
+        return false;
     }
-    int result = android::base::WriteStringToFd(content, fd) ? 0 : -1;
-    if (result == -1) {
+    bool success = android::base::WriteStringToFd(content, fd);
+    if (!success) {
         PLOG(ERROR) << "write_file: Unable to write to '" << path << "'";
     }
     close(fd);
-    return result;
+    return success;
 }
 
 boot_clock::time_point boot_clock::now() {

init/util.h

@@ -33,7 +33,7 @@ int create_socket(const char *name, int type, mode_t perm,
                   uid_t uid, gid_t gid, const char *socketcon);
 
 bool read_file(const char* path, std::string* content);
-int write_file(const char* path, const char* content);
+bool write_file(const char* path, const char* content);
 
 // A std::chrono clock based on CLOCK_BOOTTIME.
 class boot_clock {