[sql] Validate database files before enabling memory-mapping.

sql/connection.h

 // Copyright (c) 2012 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.
 
 #ifndef SQL_CONNECTION_H_
 #define SQL_CONNECTION_H_
 
 #include <stdint.h>
 #include <map>
 #include <set>
@@ skipping 186 matching lines @@
     EVENT_CHANGES_AUTOCOMMIT,
 
     // Number of rows changed by statements in transactions.
     EVENT_CHANGES,
 
     // Count actual SQLite transaction statements (not including nesting).
     EVENT_BEGIN,
     EVENT_COMMIT,
     EVENT_ROLLBACK,
 
+    // Track success and failure in GetAppropriateMmapSize().
+    // GetAppropriateMmapSize() should record at most one of these per run.  The
+    // case of mapping everything is not recorded.
+    EVENT_MMAP_META_MISSING,         // No meta table present.
+    EVENT_MMAP_META_FAILURE_READ,    // Failed reading meta table.
+    EVENT_MMAP_META_FAILURE_UPDATE,  // Failed updating meta table.
+    EVENT_MMAP_VFS_FAILURE,          // Failed to access VFS.
+    EVENT_MMAP_FAILED,               // Failure from past run.
+    EVENT_MMAP_FAILED_NEW,           // Read error in this run.
+    EVENT_MMAP_SUCCESS_NEW,          // Read to EOF in this run.
+    EVENT_MMAP_SUCCESS_PARTIAL,      // Read but did not reach EOF.
+    EVENT_MMAP_SUCCESS_NO_PROGRESS,  // Read quota exhausted.
+
     // Leave this at the end.
     // TODO(shess): |EVENT_MAX| causes compile fail on Windows.
     EVENT_MAX_VALUE
   };
   void RecordEvent(Events event, size_t count);
   void RecordOneEvent(Events event) {
     RecordEvent(event, 1);
   }
 
   // Run "PRAGMA integrity_check" and post each line of
@@ skipping 469 matching lines @@
   // database is razed or recovered, or if the diagnostic code adds new
   // capabilities.
   bool RegisterIntentToUpload() const;
 
   // Helper to collect diagnostic info for a corrupt database.
   std::string CollectCorruptionInfo();
 
   // Helper to collect diagnostic info for errors.
   std::string CollectErrorInfo(int error, Statement* stmt) const;
 
+  // Calculates a value appropriate to pass to "PRAGMA mmap_size = ".  So errors
+  // can make it unsafe to map a file, so the file is read using regular I/O,
+  // with any errors causing 0 (don't map anything) to be returned.  If the
+  // entire file is read without error, a large value is returned which will
+  // allow the entire file to be mapped in most cases.
+  //
+  // Results are recorded in the database's meta table for future reference, so
+  // the file should only be read through once.
+  size_t GetAppropriateMmapSize();
+
   // The actual sqlite database. Will be NULL before Init has been called or if
   // Init resulted in an error.
   sqlite3* db_;
 
   // Parameters we'll configure in sqlite before doing anything else. Zero means
   // use the default value.
   int page_size_;
   int cache_size_;
   bool exclusive_locking_;
   bool restrict_to_user_;
@@ skipping 63 matching lines @@
   // Source for timing information, provided to allow tests to inject time
   // changes.
   scoped_ptr<TimeSource> clock_;
 
   DISALLOW_COPY_AND_ASSIGN(Connection);
 };
 
 }  // namespace sql
 
 #endif  // SQL_CONNECTION_H_