Re: [RFC V2 11/18] famfs_fuse: Basic famfs mount opts

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Jul 03, 2025 at 01:50:25PM -0500, John Groves wrote:
> * -o shadow=<shadowpath>

What is a shadow?

> * -o daxdev=<daxdev>

And, uh, if there's a FUSE_GET_DAXDEV command, then what does this mount
option do?  Pre-populate the first element of that set?

--D

> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/fuse/fuse_i.h |  8 +++++++-
>  fs/fuse/inode.c  | 28 +++++++++++++++++++++++++++-
>  2 files changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index a592c1002861..f4ee61046578 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -583,9 +583,11 @@ struct fuse_fs_context {
>  	unsigned int blksize;
>  	const char *subtype;
>  
> -	/* DAX device, may be NULL */
> +	/* DAX device for virtiofs, may be NULL */
>  	struct dax_device *dax_dev;
>  
> +	const char *shadow; /* famfs - null if not famfs */
> +
>  	/* fuse_dev pointer to fill in, should contain NULL on entry */
>  	void **fudptr;
>  };
> @@ -941,6 +943,10 @@ struct fuse_conn {
>  	/**  uring connection information*/
>  	struct fuse_ring *ring;
>  #endif
> +
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +	char *shadow;
> +#endif
>  };
>  
>  /*
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index e48e11c3f9f3..a7e1cf8257b0 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -766,6 +766,9 @@ enum {
>  	OPT_ALLOW_OTHER,
>  	OPT_MAX_READ,
>  	OPT_BLKSIZE,
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +	OPT_SHADOW,
> +#endif
>  	OPT_ERR
>  };
>  
> @@ -780,6 +783,9 @@ static const struct fs_parameter_spec fuse_fs_parameters[] = {
>  	fsparam_u32	("max_read",		OPT_MAX_READ),
>  	fsparam_u32	("blksize",		OPT_BLKSIZE),
>  	fsparam_string	("subtype",		OPT_SUBTYPE),
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +	fsparam_string("shadow",		OPT_SHADOW),
> +#endif
>  	{}
>  };
>  
> @@ -875,6 +881,15 @@ static int fuse_parse_param(struct fs_context *fsc, struct fs_parameter *param)
>  		ctx->blksize = result.uint_32;
>  		break;
>  
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +	case OPT_SHADOW:
> +		if (ctx->shadow)
> +			return invalfc(fsc, "Multiple shadows specified");
> +		ctx->shadow = param->string;
> +		param->string = NULL;
> +		break;
> +#endif
> +
>  	default:
>  		return -EINVAL;
>  	}
> @@ -888,6 +903,7 @@ static void fuse_free_fsc(struct fs_context *fsc)
>  
>  	if (ctx) {
>  		kfree(ctx->subtype);
> +		kfree(ctx->shadow);
>  		kfree(ctx);
>  	}
>  }
> @@ -919,7 +935,10 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
>  	else if (fc->dax_mode == FUSE_DAX_INODE_USER)
>  		seq_puts(m, ",dax=inode");
>  #endif
> -
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +	if (fc->shadow)
> +		seq_printf(m, ",shadow=%s", fc->shadow);
> +#endif
>  	return 0;
>  }
>  
> @@ -1017,6 +1036,9 @@ void fuse_conn_put(struct fuse_conn *fc)
>  		}
>  		if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
>  			fuse_backing_files_free(fc);
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +		kfree(fc->shadow);
> +#endif
>  		call_rcu(&fc->rcu, delayed_release);
>  	}
>  }
> @@ -1834,6 +1856,10 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
>  	sb->s_root = root_dentry;
>  	if (ctx->fudptr)
>  		*ctx->fudptr = fud;
> +
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +	fc->shadow = kstrdup(ctx->shadow, GFP_KERNEL);
> +#endif
>  	mutex_unlock(&fuse_mutex);
>  	return 0;
>  
> -- 
> 2.49.0
> 
>