Made IO_CACHE safe for reading big blocks (> 2G)

The reason for adding this was that while testing mysqlbinlog on
a replication event with 3G event output, Linux failed reading
the whole file in memory with one read (only got 2G on first read
even if file had just been written).

- Don't reset info->error on write error in IO_CACHE.
- In case of write_error in IO_CACHE , always return -1
- Fixed wrong result from my_read when using MY_FULL_IO. Also don't give
  an error in case of retry.

mysys/mf_iocache.c

@@ -115,6 +115,7 @@ init_functions(IO_CACHE* info)
     DBUG_ASSERT(!(info->myflags & MY_ENCRYPT));
     info->read_function = info->share ? _my_b_cache_read_r : _my_b_cache_read;
     info->write_function = info->share ? _my_b_cache_write_r : _my_b_cache_write;
+    info->myflags&= ~MY_FULL_IO;
     break;
   case TYPE_NOT_SET:
     DBUG_ASSERT(0);
@@ -455,6 +456,8 @@ my_bool reinit_io_cache(IO_CACHE *info, enum cache_type type,
     {
       info->read_end=info->write_pos;
       info->end_of_file=my_b_tell(info);
+      /* Ensure we will read all data */
+      info->myflags|= MY_FULL_IO;
       /*
         Trigger a new seek only if we have a valid
         file handle.
@@ -469,6 +472,7 @@ my_bool reinit_io_cache(IO_CACHE *info, enum cache_type type,
 	info->seek_not_done=1;
       }
       info->end_of_file = ~(my_off_t) 0;
+      info->myflags&= ~MY_FULL_IO;
     }
     pos=info->request_pos+(seek_offset-info->pos_in_file);
     if (type == WRITE_CACHE)
@@ -1917,13 +1921,12 @@ int my_b_flush_io_cache(IO_CACHE *info, int need_append_buffer_lock)
     {
       if (append_cache)
       {
-
         if (mysql_file_write(info->file, info->write_buffer, length,
                              info->myflags | MY_NABP))
+        {
           info->error= -1;
-        else
-          info->error= 0;
-
+          DBUG_RETURN(-1);
+        }
         info->end_of_file+= info->write_pos - info->append_read_pos;
         info->append_read_pos= info->write_buffer;
         DBUG_ASSERT(info->end_of_file == mysql_file_tell(info->file, MYF(0)));

mysys/my_read.c

@@ -35,11 +35,10 @@
 
 size_t my_read(File Filedes, uchar *Buffer, size_t Count, myf MyFlags)
 {
-  size_t readbytes, save_count;
+  size_t readbytes, save_count= 0;
   DBUG_ENTER("my_read");
   DBUG_PRINT("my",("fd: %d  Buffer: %p  Count: %lu  MyFlags: %lu",
                    Filedes, Buffer, (ulong) Count, MyFlags));
-  save_count= Count;
   if (!(MyFlags & (MY_WME | MY_FAE | MY_FNABP)))
     MyFlags|= my_global_flags;
 
@@ -61,47 +60,52 @@ size_t my_read(File Filedes, uchar *Buffer, size_t Count, myf MyFlags)
 
     if (readbytes != Count)
     {
-      my_errno= errno;
-      if (errno == 0 || (readbytes != (size_t) -1 &&
-                         (MyFlags & (MY_NABP | MY_FNABP))))
-        my_errno= HA_ERR_FILE_TOO_SHORT;
+      int got_errno= my_errno= errno;
       DBUG_PRINT("warning",("Read only %d bytes off %lu from %d, errno: %d",
                             (int) readbytes, (ulong) Count, Filedes,
-                            my_errno));
+                            got_errno));
+
+      if (got_errno == 0 || (readbytes != (size_t) -1 &&
+                         (MyFlags & (MY_NABP | MY_FNABP))))
+        my_errno= HA_ERR_FILE_TOO_SHORT;
 
-      if ((readbytes == 0 || (int) readbytes == -1) && errno == EINTR)
+      if ((readbytes == 0 || (int) readbytes == -1) && got_errno == EINTR)
       {  
         DBUG_PRINT("debug", ("my_read() was interrupted and returned %ld",
                              (long) readbytes));
         continue;                              /* Interrupted */
       }
 
+      /* Do a read retry if we didn't get enough data on first read */
+      if (readbytes != (size_t) -1 && readbytes != 0 &&
+          (MyFlags & MY_FULL_IO))
+      {
+        Buffer+= readbytes;
+        Count-= readbytes;
+        save_count+= readbytes;
+        continue;
+      }
+
       if (MyFlags & (MY_WME | MY_FAE | MY_FNABP))
       {
         if (readbytes == (size_t) -1)
           my_error(EE_READ,
                    MYF(ME_BELL | ME_WAITTANG | (MyFlags & (ME_JUST_INFO | ME_NOREFRESH))),
-                   my_filename(Filedes),my_errno);
+                   my_filename(Filedes), got_errno);
         else if (MyFlags & (MY_NABP | MY_FNABP))
           my_error(EE_EOFERR,
                    MYF(ME_BELL | ME_WAITTANG | (MyFlags & (ME_JUST_INFO | ME_NOREFRESH))),
-                   my_filename(Filedes),my_errno);
+                   my_filename(Filedes), got_errno);
       }
       if (readbytes == (size_t) -1 ||
           ((MyFlags & (MY_FNABP | MY_NABP)) && !(MyFlags & MY_FULL_IO)))
         DBUG_RETURN(MY_FILE_ERROR);	/* Return with error */
-      if (readbytes != (size_t) -1 && (MyFlags & MY_FULL_IO))
-      {
-        Buffer+= readbytes;
-        Count-= readbytes;
-        continue;
-      }
     }
 
     if (MyFlags & (MY_NABP | MY_FNABP))
       readbytes= 0;			/* Ok on read */
-    else if (MyFlags & MY_FULL_IO)
-      readbytes= save_count;
+    else
+      readbytes+= save_count;
     break;
   }
   DBUG_RETURN(readbytes);