Make ancestor directories before writing htoprc

... and don't create config directories when reading the htop config.

The new subroutine for creating directories can also work with custom
paths specified in HTOPRC environment variable.

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

Author: Explorer09

Settings.c

@@ -563,6 +563,43 @@ static bool Settings_read(Settings* this, const char* fileName, const Machine* h
    return didReadAny;
 }
 
+static int makeAncestorDirectories(char* filePath) {
+   // The caller is expected to set the umask before calling this function.
+   // In particular, if the umask contains S_IWUSR or S_IXUSR bit then the
+   // making of subdirectories within the ancestor can fail.
+
+   // 0755 is the maximum permission we can give to directories at this phase.
+   const mode_t mode = S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH;
+
+   bool hasDirectory = false;
+   int savedErr = errno;
+
+   char *p = filePath;
+   while (true) {
+      while (*p == '/')
+         p++;
+
+      while (*p && *p != '/')
+         p++;
+
+      if (!*p)
+         break;
+
+      *p = '\0';
+      bool ok = !mkdir(filePath, mode);
+      *p = '/';
+      if (ok) {
+         hasDirectory = true;
+         errno = savedErr;
+      } else if (hasDirectory) {
+         return -errno;
+      }
+      // Try creating directories in the lower levels. It's possible for
+      // mkdir() to succeed in a lower level while an error happens earlier.
+   }
+   return 0;
+}
+
 typedef ATTR_FORMAT(printf, 2, 3) int (*OutputFunc)(FILE*, const char*,...);
 
 static void writeFields(OutputFunc of, FILE* fp,
@@ -649,9 +686,15 @@ int Settings_write(const Settings* this, bool onCrash) {
    } else if (!this->writeConfig) {
       return 0;
    } else {
-      /* create tempfile with mode 0600 */
-      mode_t cur_umask = umask(S_IXUSR | S_IRWXG | S_IRWXO);
+      // Prepare temp filename
       xAsprintf(&tmpFilename, "%s.tmp.XXXXXX", this->filename);
+
+      // Create ancestor directories with mode 0700
+      mode_t cur_umask = umask(S_IRWXG | S_IRWXO);
+      makeAncestorDirectories(tmpFilename);
+
+      // Create temp file with mode 0600
+      umask(S_IXUSR | S_IRWXG | S_IRWXO);
       int fdtmp = mkstemp(tmpFilename);
       umask(cur_umask);
       if (fdtmp == -1) {
@@ -851,8 +894,6 @@ Settings* Settings_new(const Machine* host, Hashtable* dynamicMeters, Hashtable*
          configDir = String_cat(home, CONFIGDIR);
          htopDir = String_cat(home, CONFIGDIR "/htop");
       }
-      (void) mkdir(configDir, 0700);
-      (void) mkdir(htopDir, 0700);
       free(htopDir);
       free(configDir);