Re: [PATCH 2/2] Btrfs: introduce noextiref mount option

[Jan Schmidt <list.btrfs@jan-o-sch.net>]

On Thu, April 11, 2013 at 12:35 (+0200), Miao Xie wrote:
> Now, we set incompat flag EXTEND_IREF when we actually need insert a
> extend inode reference, not when making a fs. But some users may hope
> that the fs still can be mounted on the old kernel, and don't hope we
> insert any extend inode references. So we introduce noextiref mount
> option to close this function.

That's a much better approach compared to setting the flag on mkfs, I agree.

> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
> Cc: Mark Fasheh <mfasheh@suse.de>
> ---
>  fs/btrfs/ctree.h      |  1 +
>  fs/btrfs/disk-io.c    |  9 +++++++++
>  fs/btrfs/inode-item.c |  2 +-
>  fs/btrfs/super.c      | 41 ++++++++++++++++++++++++++++++++++++++++-
>  4 files changed, 51 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index a883e47..db88963 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1911,6 +1911,7 @@ struct btrfs_ioctl_defrag_range_args {
>  #define BTRFS_MOUNT_CHECK_INTEGRITY	(1 << 20)
>  #define BTRFS_MOUNT_CHECK_INTEGRITY_INCLUDING_EXTENT_DATA (1 << 21)
>  #define BTRFS_MOUNT_PANIC_ON_FATAL_ERROR	(1 << 22)
> +#define BTRFS_MOUNT_NOEXTIREF		(1 << 23)
>  
>  #define btrfs_clear_opt(o, opt)		((o) &= ~BTRFS_MOUNT_##opt)
>  #define btrfs_set_opt(o, opt)		((o) |= BTRFS_MOUNT_##opt)
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index ab8ef37..ee00448 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2269,6 +2269,15 @@ int open_ctree(struct super_block *sb,
>  		goto fail_alloc;
>  	}
>  
> +	if ((btrfs_super_incompat_flags(disk_super) &
> +	     BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF) &&
> +	    btrfs_test_opt(tree_root, NOEXTIREF)) {
> +		printk(KERN_ERR "BTRFS: couldn't mount because the extend iref"
> +		       "can not be close.\n");
> +		err = -EINVAL;
> +		goto fail_alloc;
> +	}
> +
>  	if (btrfs_super_leafsize(disk_super) !=
>  	    btrfs_super_nodesize(disk_super)) {
>  		printk(KERN_ERR "BTRFS: couldn't mount because metadata "
> diff --git a/fs/btrfs/inode-item.c b/fs/btrfs/inode-item.c
> index f07eb45..7c4f880 100644
> --- a/fs/btrfs/inode-item.c
> +++ b/fs/btrfs/inode-item.c
> @@ -442,7 +442,7 @@ int btrfs_insert_inode_ref(struct btrfs_trans_handle *trans,
>  out:
>  	btrfs_free_path(path);
>  
> -	if (ret == -EMLINK) {
> +	if (ret == -EMLINK && !btrfs_test_opt(root, NOEXTIREF)) {
>  		/*
>  		 * We ran out of space in the ref array. Need to add an
>  		 * extended ref.
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 0f03569..fd375b3 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -315,7 +315,7 @@ enum {
>  	Opt_nodatacow, Opt_max_inline, Opt_alloc_start, Opt_nobarrier, Opt_ssd,
>  	Opt_nossd, Opt_ssd_spread, Opt_thread_pool, Opt_noacl, Opt_compress,
>  	Opt_compress_type, Opt_compress_force, Opt_compress_force_type,
> -	Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_discard,
> +	Opt_notreelog, Opt_noextiref, Opt_ratio, Opt_flushoncommit, Opt_discard,
>  	Opt_space_cache, Opt_clear_cache, Opt_user_subvol_rm_allowed,
>  	Opt_enospc_debug, Opt_subvolrootid, Opt_defrag, Opt_inode_cache,
>  	Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
> @@ -344,6 +344,7 @@ static match_table_t tokens = {
>  	{Opt_nossd, "nossd"},
>  	{Opt_noacl, "noacl"},
>  	{Opt_notreelog, "notreelog"},
> +	{Opt_noextiref, "noextiref"},
>  	{Opt_flushoncommit, "flushoncommit"},
>  	{Opt_ratio, "metadata_ratio=%d"},
>  	{Opt_discard, "discard"},
> @@ -535,6 +536,10 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
>  			printk(KERN_INFO "btrfs: disabling tree log\n");
>  			btrfs_set_opt(info->mount_opt, NOTREELOG);
>  			break;
> +		case Opt_noextiref:
> +			printk(KERN_INFO "btrfs: disabling extend inode ref\n");
> +			btrfs_set_opt(info->mount_opt, NOEXTIREF);
> +			break;
>  		case Opt_flushoncommit:
>  			printk(KERN_INFO "btrfs: turning on flush-on-commit\n");
>  			btrfs_set_opt(info->mount_opt, FLUSHONCOMMIT);
> @@ -1202,6 +1207,35 @@ static void btrfs_resize_thread_pool(struct btrfs_fs_info *fs_info,
>  			      new_pool_size);
>  }
>  
> +static int btrfs_close_extend_iref(struct btrfs_fs_info *fs_info,
> +				   unsigned long old_opts)

The name irritated me, it's more like "unset" instead of "close", isn't it?

> +{
> +	struct btrfs_trans_handle *trans;
> +	int ret;
> +
> +	if (btrfs_raw_test_opt(old_opts, NOEXTIREF) ||
> +	    !btrfs_raw_test_opt(fs_info->mount_opt, NOEXTIREF))
> +		return 0;
> +
> +	trans = btrfs_attach_transaction(fs_info->tree_root);
> +	if (IS_ERR(trans)) {
> +		if (PTR_ERR(trans) != -ENOENT)
> +			return PTR_ERR(trans);
> +	} else {
> +		ret = btrfs_commit_transaction(trans, fs_info->tree_root);
> +		if (ret)
> +			return ret;
> +	}

Huh? I don't see why we need to commit the transaction here. Can you please explain?

Thanks,
-Jan

> +
> +	if (btrfs_super_incompat_flags(fs_info->super_copy) &
> +	    BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF) {
> +		printk(KERN_ERR "BTRFS: could not close extend iref.\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static inline void btrfs_remount_prepare(struct btrfs_fs_info *fs_info)
>  {
>  	set_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state);
> @@ -1259,6 +1293,11 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>  	}
>  
>  	btrfs_remount_begin(fs_info, old_opts, *flags);
> +
> +	ret = btrfs_close_extend_iref(fs_info, old_opts);
> +	if (ret)
> +		goto restore;
> +
>  	btrfs_resize_thread_pool(fs_info,
>  		fs_info->thread_pool_size, old_thread_pool_size);
>  
>