Re: [PATCH RFC] libfs: getdents() should return 0 after reaching EOD

[Matthew Wilcox <willy@infradead.org>]

On Tue, Nov 14, 2023 at 10:49:37AM -0500, Chuck Lever wrote:
> -static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
> +static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
>  {
>  	struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode);
>  	XA_STATE(xas, &so_ctx->xa, ctx->pos);
> @@ -437,7 +437,8 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
>  	while (true) {
>  		dentry = offset_find_next(&xas);
>  		if (!dentry)
> -			break;
> +			/* readdir has reached the current EOD */
> +			return (void *)0x10;

Funny, you used the same bit pattern as ZERO_SIZE_PTR without using
the macro ...

> @@ -479,7 +481,12 @@ static int offset_readdir(struct file *file, struct dir_context *ctx)
>  	if (!dir_emit_dots(file, ctx))
>  		return 0;
>  
> -	offset_iterate_dir(d_inode(dir), ctx);
> +	if (ctx->pos == 2)
> +		file->private_data = NULL;
> +	else if (file->private_data == (void *)0x10)
> +		return 0;
> +
> +	file->private_data = offset_iterate_dir(d_inode(dir), ctx);
>  	return 0;
>  }

It might make more sense to use ERR_PTR(-ENOENT) or ERANGE or something
that's a more understandable sentinel value?