SERVER-9248 Ignore errors when checking readahead

To test, run sudo chmod o-x /sys/dev/block
Manual backport of commit 9501c1bfce47079de54e0aba7b78bae341e3e916

1 files changed, 31 insertions, 23 deletions

diff --git a/src/mongo/db/db.cpp b/src/mongo/db/db.cpp
index b66cd60d913..29d470f39e0 100644
--- a/src/mongo/db/db.cpp
+++ b/src/mongo/db/db.cpp
@@ -543,38 +543,46 @@ namespace mongo {
     /// warn if readahead > 256KB (gridfs chunk size)
     static void checkReadAhead(const string& dir) {
 #ifdef __linux__
-        const dev_t dev = getPartition(dir);
-
-        // This path handles the case where the filesystem uses the whole device (including LVM)
-        string path = str::stream() <<
-            "/sys/dev/block/" << major(dev) << ':' << minor(dev) << "/queue/read_ahead_kb";
-
-        if (!boost::filesystem::exists(path)){
-            // This path handles the case where the filesystem is on a partition.
-            path = str::stream()
-                << "/sys/dev/block/" << major(dev) << ':' << minor(dev) // this is a symlink
-                << "/.." // parent directory of a partition is for the whole device
-                << "/queue/read_ahead_kb";
-        }
+        try { 
+            const dev_t dev = getPartition(dir);
+
+            // This path handles the case where the filesystem uses the whole device (including LVM)
+            string path = str::stream() <<
+                "/sys/dev/block/" << major(dev) << ':' << minor(dev) << "/queue/read_ahead_kb";
+
+            if (!boost::filesystem::exists(path)){
+                // This path handles the case where the filesystem is on a partition.
+                path = str::stream()
+                    << "/sys/dev/block/" << major(dev) << ':' << minor(dev) // this is a symlink
+                    << "/.." // parent directory of a partition is for the whole device
+                    << "/queue/read_ahead_kb";
+            }
 
-        if (boost::filesystem::exists(path)) {
-            ifstream file (path.c_str());
-            if (file.is_open()) {
-                int kb;
-                file >> kb;
-                if (kb > 256) {
-                    log() << startupWarningsLog;
+            if (boost::filesystem::exists(path)) {
+                ifstream file (path.c_str());
+                if (file.is_open()) {
+                    int kb;
+                    file >> kb;
+                    if (kb > 256) {
+                        log() << startupWarningsLog;
 
-                    log() << "** WARNING: Readahead for " << dir << " is set to " << kb << "KB"
+                        log() << "** WARNING: Readahead for " << dir << " is set to " << kb << "KB"
                             << startupWarningsLog;
 
-                    log() << "**          We suggest setting it to 256KB (512 sectors) or less"
+                        log() << "**          We suggest setting it to 256KB (512 sectors) or less"
                             << startupWarningsLog;
 
-                    log() << "**          http://dochub.mongodb.org/core/readahead"
+                        log() << "**          http://dochub.mongodb.org/core/readahead"
                             << startupWarningsLog;
+                    }
                 }
             }
+            catch (const std::exception& e) {
+                log() << "unable to validate readahead settings due to error: " << e.what()
+                    << startupWarningsLog;
+                log() << "for more information, see http://dochub.mongodb.org/core/readahead"
+                    << startupWarningsLog;
+            }
         }
 #endif // __linux__
     }