Trying again to land OOM priority manager changes.

sandbox/linux/suid/process_util_linux.c

-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The following is the C version of code from base/process_utils_linux.cc.
 // We shouldn't link against C++ code in a setuid binary.
 
 #define _GNU_SOURCE  // needed for O_DIRECTORY
 
 #include "process_util.h"
 
 #include <fcntl.h>
 #include <inttypes.h>
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 
+// Ranges for the current (oom_score_adj) and previous (oom_adj)
+// flavors of OOM score.
+static const int kMaxOomScore = 1000;
+static const int kMaxOldOomScore = 15;
+
 bool AdjustOOMScore(pid_t process, int score) {
-  if (score < 0 || score > 15)
+  if (score < 0 || score > kMaxOomScore)
     return false;
 
   char oom_adj[27];  // "/proc/" + log_10(2**64) + "\0"
                      //    6     +       20     +     1         = 27
   snprintf(oom_adj, sizeof(oom_adj), "/proc/%" PRIdMAX, (intmax_t)process);
 
   const int dirfd = open(oom_adj, O_RDONLY | O_DIRECTORY);
   if (dirfd < 0)
     return false;
 
   struct stat statbuf;
   if (fstat(dirfd, &statbuf) < 0) {
     close(dirfd);
     return false;
   }
   if (getuid() != statbuf.st_uid) {
     close(dirfd);
     return false;
   }
 
-  const int fd = openat(dirfd, "oom_adj", O_WRONLY);
+  int fd = openat(dirfd, "oom_score_adj", O_WRONLY);
+  if (fd < 0) {
+    // We failed to open oom_score_adj, so let's try for the older
+    // oom_adj file instead.
+    fd = openat(dirfd, "oom_adj", O_WRONLY);
+    if (fd < 0) {
+      // Nope, that doesn't work either.
+      return false;
+    } else {
+      // If we're using the old oom_adj file, the allowed range is now
+      // [0, kMaxOldOomScore], so we scale the score.  This may result in some
+      // aliasing of values, of course.
+      score = score * kMaxOldOomScore / kMaxOomScore;
+    }
+  }
   close(dirfd);
 
-  if (fd < 0)
-    return false;
-
-  char buf[3];  // 0 <= |score| <= 15;
+  char buf[11];  // 0 <= |score| <= kMaxOomScore; using log_10(2**32) + 1 size
   snprintf(buf, sizeof(buf), "%d", score);
   size_t len = strlen(buf);
 
   ssize_t bytes_written = write(fd, buf, len);
   close(fd);
   return (bytes_written == len);
 }