Re: [PATCH v3 1/4] btrfs: support remount of ro fs with free space tree

[David Sterba <dsterba@suse.cz>]

On Thu, Sep 17, 2020 at 11:13:38AM -0700, Boris Burkov wrote:
>  #include "block-group.h"
>  #include "discard.h"
> +#include "free-space-tree.h"
>  
>  #include "qgroup.h"
>  #define CREATE_TRACE_POINTS
> @@ -1838,6 +1839,7 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>  	u64 old_max_inline = fs_info->max_inline;
>  	u32 old_thread_pool_size = fs_info->thread_pool_size;
>  	u32 old_metadata_ratio = fs_info->metadata_ratio;
> +	bool create_fst = false;
>  	int ret;
>  
>  	sync_filesystem(sb);
> @@ -1862,6 +1864,16 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>  	btrfs_resize_thread_pool(fs_info,
>  		fs_info->thread_pool_size, old_thread_pool_size);
>  
> +	if (btrfs_test_opt(fs_info, FREE_SPACE_TREE) &&
> +	    !btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE)) {
> +		create_fst = true;
> +		if (!sb_rdonly(sb) || *flags & SB_RDONLY) {
> +			btrfs_warn(fs_info,
> +				   "Remounting with free space tree only supported from read-only to read-write");

lowercase for start of the sting, unindent it so ends below 80 columns

> +			create_fst = false;
> +		}
> +	}
> +
>  	if ((bool)(*flags & SB_RDONLY) == sb_rdonly(sb))
>  		goto out;
>  
> @@ -1924,6 +1936,21 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>  			goto restore;
>  		}
>  
> +		/*
> +		 * NOTE: when remounting with a change that does writes, don't
> +		 * put it anywhere above this point, as we are not sure to be
> +		 * safe to write until we pass the above checks.
> +		 */
> +		if (create_fst) {
> +			ret = btrfs_create_free_space_tree(fs_info);
> +			if (ret) {
> +				btrfs_warn(fs_info,
> +					   "failed to create free space tree: %d", ret);

same

> +				goto restore;
> +			}
> +		}
> +
> +
>  		ret = btrfs_cleanup_fs_roots(fs_info);
>  		if (ret)
>  			goto restore;
> -- 
> 2.24.1