Return correct disk free/available size when FS is mounted with size = 0

base/sys_info_posix.cc

 // 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.
 
 #include "base/sys_info.h"
 
 #include <errno.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
@@ skipping 10 matching lines @@
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 
 #if defined(OS_ANDROID)
 #include <sys/vfs.h>
 #define statvfs statfs  // Android uses a statvfs-like statfs struct and call.
 #else
 #include <sys/statvfs.h>
 #endif
 
+#if defined(OS_LINUX)
+#include <linux/magic.h>
+#endif
+
 namespace {
 
 #if !defined(OS_OPENBSD)
 int NumberOfProcessors() {
   // sysconf returns the number of "logical" (not "physical") processors on both
   // Mac and Linux.  So we get the number of max available "logical" processors.
   //
   // Note that the number of "currently online" processors may be fewer than the
   // returned value of NumberOfProcessors(). On some platforms, the kernel may
   // make some processors offline intermittently, to save power when system
@@ skipping 25 matching lines @@
     NOTREACHED();
     return 0;
   }
   return limit.rlim_cur == RLIM_INFINITY ? 0 : limit.rlim_cur;
 }
 
 base::LazyInstance<
     base::internal::LazySysInfoValue<int64_t, AmountOfVirtualMemory>>::Leaky
     g_lazy_virtual_memory = LAZY_INSTANCE_INITIALIZER;
 
+#if defined(OS_LINUX)
+bool IsStatsZeroIfUnlimited(unsigned long int fsid) {
+  // On Linux, stats.f_blocks is 0 when memory based file system (like tmpfs,
+  // ramfs, or hugetlbfs), is mounted without any size limit (i.e. size set to
+  // 0).
+  return fsid == TMPFS_MAGIC || fsid == HUGETLBFS_MAGIC || fsid == RAMFS_MAGIC;
+}
+#endif
+
 bool GetDiskSpaceInfo(const base::FilePath& path,
                       int64_t* available_bytes,
                       int64_t* total_bytes) {
   struct statvfs stats;
   if (HANDLE_EINTR(statvfs(path.value().c_str(), &stats)) != 0)
     return false;
 
-  if (available_bytes)
-    *available_bytes = static_cast<int64_t>(stats.f_bavail) * stats.f_frsize;
-  if (total_bytes)
-    *total_bytes = static_cast<int64_t>(stats.f_blocks) * stats.f_frsize;
+#if defined(OS_LINUX)
+  const bool zero_size_means_unlimited =
+      stats.f_blocks == 0 && IsStatsZeroIfUnlimited(stats.f_fsid);

[Lei Zhang, 2016/08/01 21:30:55]

Are you sure f_fsid is the right field to check? Locally I ran this program:

#include <stdio.h>
#include <sys/statvfs.h>

int main() {
  struct statvfs stats;
  statvfs("/run/shm/foo", &stats);
  printf("%lu\n", stats.f_fsid);
  return 0;
}

and it returned 0, for a file foo that exists on /run/shm, which is tmpfs.

[Sriram, 2016/08/02 00:03:24]

You are right - I misunderstood the man page and f_fsid is not the same as
f_type and f_type is not exposed via statvfs() call. Switched to statfs() as all
values needed here is available.

+#else
+  const bool zero_size_means_unlimited = false;
+#endif
+
+  if (available_bytes) {
+    *available_bytes =
+        zero_size_means_unlimited
+            ? std::numeric_limits<int64_t>::max()
+            : static_cast<int64_t>(stats.f_bavail) * stats.f_frsize;
+  }
+
+  if (total_bytes) {
+    *total_bytes = zero_size_means_unlimited
+                       ? std::numeric_limits<int64_t>::max()
+                       : static_cast<int64_t>(stats.f_blocks) * stats.f_frsize;
+  }
+
   return true;
 }
 
 }  // namespace
 
 namespace base {
 
 #if !defined(OS_OPENBSD)
 int SysInfo::NumberOfProcessors() {
   return g_lazy_number_of_processors.Get().value();
@@ skipping 64 matching lines @@
   }
   return arch;
 }
 
 // static
 size_t SysInfo::VMAllocationGranularity() {
   return getpagesize();
 }
 
 }  // namespace base