Excerpts from liubo's message of 2011-01-06 06:30:25 -0500:
>
> This patch comes from "Forced readonly mounts on errors" ideas.
>
> As we know, this is the first step in being more fault tolerant of disk
> corruptions instead of just using BUG() statements.
>
> The major content:
> - add a framework for generating errors that should result in filesystems
> going readonly.
> - keep FS state in disk super block.
> - make sure that all of resource will be freed and released at umount time.
> - make sure that after FS is forced readonly on error, there will be no more
> disk change before FS is corrected. For this, we should stop write
> operation.
>
> After this patch is applied, the conversion from BUG() to such a framework can
> happen incrementally.
I think this is a good overall framework and it will meet our needs
nicely as we scale up the error handling in the filesystem.
One concern I have is where we save the error state to disk:
> +static void __save_error_info(struct btrfs_fs_info *fs_info)
> +{
> + struct btrfs_super_block *disk_super = &fs_info->super_copy;
> +
> + fs_info->fs_state = BTRFS_SUPER_FLAG_ERROR;
> + disk_super->flags |= cpu_to_le64(BTRFS_SUPER_FLAG_ERROR);
> +
> + mutex_lock(&fs_info->trans_mutex);
> + memcpy(&fs_info->super_for_commit, disk_super,
> + sizeof(fs_info->super_for_commit));
> + mutex_unlock(&fs_info->trans_mutex);
The super_for_commit isn't changed until we have a fully consistent set
of fields in the super block. The super_copy is changed as the
transaction progresses.
So, this memcpy isn't quite safe. We should simply set the flag on the
super_for_commit and the super_copy individually.
I'll make this change and pull it in. We can build from here.
-chris
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