Repair DBs with trailing slash in name

Summary:
Problem:

- `DB::SanitizeOptions` strips trailing slash from `wal_dir` but not `dbname`
- We check whether `wal_dir` and `dbname` refer to the same directory using string equality: https://github.com/facebook/rocksdb/blob/master/db/repair.cc#L258
- Providing `dbname` with trailing slash causes default `wal_dir` to be misidentified as a separate directory.
- Then the repair tries to add all SST files to the `VersionEdit` twice (once for `dbname` dir, once for `wal_dir`) and fails with coredump.

Solution:

- Add a new `Env` function, `AreFilesSame`, which uses device and inode number to check whether files are the same. It's currently only implemented in `PosixEnv`.
- Migrate repair to use `AreFilesSame` to check whether `dbname` and `wal_dir` are same. If unsupported, falls back to string comparison.
Closes https://github.com/facebook/rocksdb/pull/2827

Differential Revision: D5761349

Pulled By: ajkr

fbshipit-source-id: c839d548678b742af1166d60b09abd94e5476238

db/repair.cc

@@ -254,14 +254,21 @@ class Repairer {
     }
 
     // search wal_dir if user uses a customize wal_dir
-    if (!db_options_.wal_dir.empty() && 
-        db_options_.wal_dir != dbname_) {
+    bool same = false;
+    Status status = env_->AreFilesSame(db_options_.wal_dir, dbname_, &same);
+    if (status.IsNotSupported()) {
+      same = db_options_.wal_dir == dbname_;
+      status = Status::OK();
+    } else if (!status.ok()) {
+      return status;
+    }
+
+    if (!same) {
       to_search_paths.push_back(db_options_.wal_dir);
     }
 
     for (size_t path_id = 0; path_id < to_search_paths.size(); path_id++) {
-      Status status =
-          env_->GetChildren(to_search_paths[path_id], &filenames);
+      status = env_->GetChildren(to_search_paths[path_id], &filenames);
       if (!status.ok()) {
         return status;
       }

db/repair_test.cc

@@ -309,6 +309,25 @@ TEST_F(RepairTest, RepairColumnFamilyOptions) {
   }
 }
 
+TEST_F(RepairTest, DbNameContainsTrailingSlash) {
+  {
+    bool tmp;
+    if (env_->AreFilesSame("", "", &tmp).IsNotSupported()) {
+      fprintf(stderr,
+              "skipping RepairTest.DbNameContainsTrailingSlash due to "
+              "unsupported Env::AreFilesSame\n");
+      return;
+    }
+  }
+
+  Put("key", "val");
+  Flush();
+  Close();
+
+  ASSERT_OK(RepairDB(dbname_ + "/", CurrentOptions()));
+  Reopen(CurrentOptions());
+  ASSERT_EQ(Get("key"), "val");
+}
 #endif  // ROCKSDB_LITE
 }  // namespace rocksdb
 

env/env_posix.cc

@@ -23,6 +23,7 @@
 #ifdef OS_LINUX
 #include <sys/statfs.h>
 #include <sys/syscall.h>
+#include <sys/sysmacros.h>
 #endif
 #include <sys/time.h>
 #include <sys/types.h>
@@ -592,6 +593,26 @@ class PosixEnv : public Env {
     return result;
   }
 
+  virtual Status AreFilesSame(const std::string& first,
+                              const std::string& second, bool* res) override {
+    struct stat statbuf[2];
+    if (stat(first.c_str(), &statbuf[0]) != 0) {
+      return IOError("stat file", first, errno);
+    }
+    if (stat(second.c_str(), &statbuf[1]) != 0) {
+      return IOError("stat file", second, errno);
+    }
+
+    if (major(statbuf[0].st_dev) != major(statbuf[1].st_dev) ||
+        minor(statbuf[0].st_dev) != minor(statbuf[1].st_dev) ||
+        statbuf[0].st_ino != statbuf[1].st_ino) {
+      *res = false;
+    } else {
+      *res = true;
+    }
+    return Status::OK();
+  }
+
   virtual Status LockFile(const std::string& fname, FileLock** lock) override {
     *lock = nullptr;
     Status result;

include/rocksdb/env.h

@@ -261,6 +261,11 @@ class Env {
     return Status::NotSupported("LinkFile is not supported for this Env");
   }
 
+  virtual Status AreFilesSame(const std::string& first,
+                              const std::string& second, bool* res) {
+    return Status::NotSupported("AreFilesSame is not supported for this Env");
+  }
+
   // Lock the specified file.  Used to prevent concurrent access to
   // the same db by multiple processes.  On failure, stores nullptr in
   // *lock and returns non-OK.
@@ -980,6 +985,11 @@ class EnvWrapper : public Env {
     return target_->LinkFile(s, t);
   }
 
+  Status AreFilesSame(const std::string& first, const std::string& second,
+                      bool* res) override {
+    return target_->AreFilesSame(first, second, res);
+  }
+
   Status LockFile(const std::string& f, FileLock** l) override {
     return target_->LockFile(f, l);
   }