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

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Date:   Mon, 02 Jul 2018 14:23:42 +0800
From:   Huaisheng Ye <yehs2007@...o.com>
To:     "\"Al Viro\"" <viro@...IV.linux.org.uk>
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 Mon, 02 Jul 2018 03:26:00 +0800 Al Viro <viro@...IV.linux.org.uk> wrote ---- 
 > 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?

Sorry for my inaccuracy.
The type of iomap->offset is loff_t, is it better to cast first_block
to loff_t, then do the left shift operation?
 
 >  
 > > -    iomap->offset = (u64)first_block << blkbits; 
 > > +    iomap->offset = (loff_t)first_block << blkbits; 
 > 

---
Cheers,
Huaisheng