[RFC PATCH v1.1 2/2] erofs: dax support for non-tailpacking regular file

[Gao Xiang]

Hi Darrick,

On Thu, Jul 08, 2021 at 06:47:19PM -0700, Darrick J. Wong wrote:
> On Mon, Jul 05, 2021 at 09:21:53PM +0800, Gao Xiang wrote:

...

> >  	Opt_cache_strategy,
> > +	Opt_dax,
> >  	Opt_err
> >  };
> >  
> > @@ -370,6 +372,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
> >  	fsparam_flag_no("acl",		Opt_acl),
> >  	fsparam_enum("cache_strategy",	Opt_cache_strategy,
> >  		     erofs_param_cache_strategy),
> > +	fsparam_flag("dax",             Opt_dax),
> >  	{}
> >  };
> >  
> > @@ -410,6 +413,14 @@ static int erofs_fc_parse_param(struct fs_context *fc,
> >  		ctx->cache_strategy = result.uint_32;
> >  #else
> >  		errorfc(fc, "compression not supported, cache_strategy ignored");
> > +#endif
> > +		break;
> > +	case Opt_dax:
> > +#ifdef CONFIG_FS_DAX
> > +		warnfc(fc, "DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
> > +		set_opt(ctx, DAX);
> 
> You might want to allow 'dax=always' and 'dax=never' to maintain parity
> with xfs/ext4's mount options...

Yeah, thanks for your suggestion. Will revise in the next version..

(Also, more use case details and development status about this scenario
 will be shown in the following months...)

Thanks,
Gao Xiang


> 
> --D
> 
> > +#else
> > +		errorfc(fc, "dax options not supported");
> >  #endif
> >  		break;
> >  	default:
> > @@ -496,10 +507,17 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
> >  		return -ENOMEM;
> >  
> >  	sb->s_fs_info = sbi;
> > +	sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
> >  	err = erofs_read_superblock(sb);
> >  	if (err)
> >  		return err;
> >  
> > +	if (test_opt(ctx, DAX) &&
> > +	    !bdev_dax_supported(sb->s_bdev, EROFS_BLKSIZ)) {
> > +		errorfc(fc, "DAX unsupported by block device. Turning off DAX.");
> > +		clear_opt(ctx, DAX);
> > +	}
> > +
> >  	sb->s_flags |= SB_RDONLY | SB_NOATIME;
> >  	sb->s_maxbytes = MAX_LFS_FILESIZE;
> >  	sb->s_time_gran = 1;
> > @@ -609,6 +627,8 @@ static void erofs_kill_sb(struct super_block *sb)
> >  	sbi = EROFS_SB(sb);
> >  	if (!sbi)
> >  		return;
> > +	if (sbi->dax_dev)
> > +		fs_put_dax(sbi->dax_dev);
> >  	kfree(sbi);
> >  	sb->s_fs_info = NULL;
> >  }
> > @@ -711,8 +731,8 @@ static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)
> >  
> >  static int erofs_show_options(struct seq_file *seq, struct dentry *root)
> >  {
> > -	struct erofs_sb_info *sbi __maybe_unused = EROFS_SB(root->d_sb);
> > -	struct erofs_fs_context *ctx __maybe_unused = &sbi->ctx;
> > +	struct erofs_sb_info *sbi = EROFS_SB(root->d_sb);
> > +	struct erofs_fs_context *ctx = &sbi->ctx;
> >  
> >  #ifdef CONFIG_EROFS_FS_XATTR
> >  	if (test_opt(ctx, XATTR_USER))
> > @@ -734,6 +754,8 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
> >  	else if (ctx->cache_strategy == EROFS_ZIP_CACHE_READAROUND)
> >  		seq_puts(seq, ",cache_strategy=readaround");
> >  #endif
> > +	if (test_opt(ctx, DAX))
> > +		seq_puts(seq, ",dax");
> >  	return 0;
> >  }
> >  
> > -- 
> > 2.24.4
> >