shared_memory: improve error messages on failure.

Be careful to leave errno untouched if the file open fails, so that
the latter logging statements that print errno will print the right
message.  Also format the logging text such that the perror-like
output (appending text like ": Permission denied") makes more sense.

Previously we'd end up printing text like
   Try [...] to fix.: Permission denied

BUG=57305
TEST=shared_memory_unittest should still pass

Review URL: http://codereview.chromium.org/3517003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@60986 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 11 insertions, 4 deletions

diff --git a/base/shared_memory_posix.cc b/base/shared_memory_posix.cc
index 32b3dae7..7283cbd 100644
--- a/base/shared_memory_posix.cc
+++ b/base/shared_memory_posix.cc
@@ -161,7 +161,8 @@ bool SharedMemory::CreateOrOpen(const std::string& name,
     // Deleting the file prevents anyone else from mapping it in
     // (making it private), and prevents the need for cleanup (once
     // the last fd is closed, it is truly freed).
-    file_util::Delete(path, false);
+    if (fp)
+      file_util::Delete(path, false);
   } else {
     if (!FilePathForMemoryName(name, &path))
       return false;
@@ -189,9 +190,15 @@ bool SharedMemory::CreateOrOpen(const std::string& name,
   if (fp == NULL) {
     if (posix_flags & O_CREAT) {
 #if !defined(OS_MACOSX)
-      PLOG(FATAL) << "Creating shared memory in " << path.value() << " failed. "
-                  << "This is frequently caused by incorrect permissions on "
-                  << "/dev/shm.  Try 'sudo chmod 777 /dev/shm' to fix.";
+      PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
+      FilePath dir = path.DirName();
+      if (access(dir.value().c_str(), W_OK | X_OK) < 0) {
+        PLOG(ERROR) << "Unable to access(W_OK|X_OK) " << dir.value();
+        if (dir.value() == "/dev/shm") {
+          LOG(FATAL) << "This is frequently caused by incorrect permissions on "
+                     << "/dev/shm.  Try 'sudo chmod 777 /dev/shm' to fix.";
+        }
+      }
 #else
       PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
 #endif