Re: [Yaffs] Periodic Checkpointing

On Saturday 03 April 2010 04:12:39 Jean-Loup Sabatier wrote:
> Good morning Josh, Good morning all,
>
> We use to force a YAFFS2 checkpoint (in a Linux root filesystem) after a
> modification and when we're not going to change it anymore for some time.
> For that we're remounting the partition in read only (it's a fake "remount"
> in "read-only", i.e. we could still write in the file system, but it just
> forces the check point).
>

Jean-Loup
Does this do anything more than sync() with yaffs_auto_checkpoint set
correctly?

One limitation I see with the current sync() method is that it always does
what is in yaffs_auto_checkpoint. If the mount is not dirtied then changing
the yaffs_auto_checkpoint and re-syncing will not result in a checkpoint.

eg.
echo 0 > /sys/modules/yaffs2/parameters/yaffs2_auto_checkpoint
sync
echo 2 > /sys/modules/yaffs2/parameters/yaffs2_auto_checkpoint
sync
will not write a checkpoint since the superblock is not dirty in the second
sync

Perhaps the following is a good idea:
--- a/yaffs_fs.c
+++ b/yaffs_fs.c
@@ -1935,20 +1935,28 @@ static void yaffs_FlushSuperBlock(struct super_block
*sb, int do_check

 static int yaffs_do_sync_fs(struct super_block *sb, int do_checkpoint)
 {
-
        yaffs_Device *dev = yaffs_SuperToDevice(sb);
+       unsigned int current_auto;
+
+       /* Todo race conditions? */
+       current_auto=yaffs_auto_checkpoint;
+
        T(YAFFS_TRACE_OS | YAFFS_TRACE_SYNC, 
                ("yaffs_do_sync_fs: %s %s\n", 
                sb->s_dirt ? "dirty" : "clean",
                do_checkpoint ? "with checkpoint" : "no checkpoint"));

-       if (sb->s_dirt) {
+       if (sb->s_dirt || (current_auto & 4)) {
                yaffs_GrossLock(dev);
                yaffs_FlushSuperBlock(sb,do_checkpoint);
                yaffs_GrossUnlock(dev);

                sb->s_dirt = 0;
        }
+
+       if(current_auto & 4)
+               yaffs_auto_checkpoint &= 3;
+
        return 0;
 }

Now a checkpoint can be forced by the following:

echo 0 > /sys/modules/yaffs2/parameters/yaffs2_auto_checkpoint
sync
echo 4 > /sys/modules/yaffs2/parameters/yaffs2_auto_checkpoint
sync

The above allows the sync to force a checkpoint by writing a value with bit
0x04 set. This will be cleared as soon as the checkpoint has been written
which makes the forcing a "one-shot".


-- Charles