linux-ext4 - Re: [PATCH 2/3] fs/ext2/inode: Fix a type cast error for fsdax

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Date:   Sun, 1 Jul 2018 20:26:00 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Huaisheng Ye <yehs2007@...o.com>
Cc:     dan.j.williams@...el.com, dave.jiang@...el.com,
        willy@...radead.org, ross.zwisler@...ux.intel.com,
        vishal.l.verma@...el.com, jack@...e.com, chengnt@...ovo.com,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org, Huaisheng Ye <yehs1@...ovo.com>
Subject: Re: [PATCH 2/3] fs/ext2/inode: Fix a type cast error for fsdax

On Sun, Jul 01, 2018 at 02:18:47PM +0800, Huaisheng Ye wrote:
> From: Huaisheng Ye <yehs1@...ovo.com>
> 
> The type of offset within struct iomap is loff_t, which represents
> file offset of mapping.
> 
> In ext2_iomap_begin, iomap->offset shall be given a type cast as
> loff_t instead of u64.

Why is it an error?  loff_t is uniformly typedefed to long long.
In which case the second variant is different from the first one
*and* does not step into nasal demon territory?

> -	iomap->offset = (u64)first_block << blkbits;
> +	iomap->offset = (loff_t)first_block << blkbits;