From: Jan Kara <jack@suse.cz>
To: Huaisheng Ye <yehs2007@zoho.com>
Cc: linux-nvdimm@lists.01.org, chengnt@lenovo.com,
linux-kernel@vger.kernel.org, willy@infradead.org,
"\"Al Viro\"" <viro@ZenIV.linux.org.uk>,
jack@suse.com, linux-ext4@vger.kernel.org
Subject: Re: [PATCH 2/3] fs/ext2/inode: Fix a type cast error for fsdax
Date: Mon, 2 Jul 2018 09:55:43 +0200 [thread overview]
Message-ID: <20180702075543.k7y73aj3s3gp4ptz@quack2.suse.cz> (raw)
In-Reply-To: <16459a9432e.10c419704327.5268154349116077352@zoho.com>
On Mon 02-07-18 14:23:42, Huaisheng Ye wrote:
> ---- On Mon, 02 Jul 2018 03:26:00 +0800 Al Viro <viro@ZenIV.linux.org.uk> wrote ----
> > On Sun, Jul 01, 2018 at 02:18:47PM +0800, Huaisheng Ye wrote:
> > > From: Huaisheng Ye <yehs1@lenovo.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?
I think what Al meant is that in the kernel loff_t is 64-bit anyway and
furthermore it is signed which means most people have to look up C standard
to remember how right shift is (un)defined if it would overflow ;). So this
does not really make the code any more readable. Rather on contrary...
Honza
>
> >
> > > - iomap->offset = (u64)first_block << blkbits;
> > > + iomap->offset = (loff_t)first_block << blkbits;
> >
>
> ---
> Cheers,
> Huaisheng
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
_______________________________________________
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Linux-nvdimm@lists.01.org
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WARNING: multiple messages have this Message-ID (diff)
From: Jan Kara <jack@suse.cz>
To: Huaisheng Ye <yehs2007@zoho.com>
Cc: "\"Al Viro\"" <viro@ZenIV.linux.org.uk>,
dan.j.williams@intel.com, dave.jiang@intel.com,
willy@infradead.org, ross.zwisler@linux.intel.com,
vishal.l.verma@intel.com, jack@suse.com, chengnt@lenovo.com,
linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org,
linux-ext4@vger.kernel.org, "\"Huaisheng Ye\"" <yehs1@lenovo.com>
Subject: Re: [PATCH 2/3] fs/ext2/inode: Fix a type cast error for fsdax
Date: Mon, 2 Jul 2018 09:55:43 +0200 [thread overview]
Message-ID: <20180702075543.k7y73aj3s3gp4ptz@quack2.suse.cz> (raw)
In-Reply-To: <16459a9432e.10c419704327.5268154349116077352@zoho.com>
On Mon 02-07-18 14:23:42, Huaisheng Ye wrote:
> ---- On Mon, 02 Jul 2018 03:26:00 +0800 Al Viro <viro@ZenIV.linux.org.uk> wrote ----
> > On Sun, Jul 01, 2018 at 02:18:47PM +0800, Huaisheng Ye wrote:
> > > From: Huaisheng Ye <yehs1@lenovo.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?
I think what Al meant is that in the kernel loff_t is 64-bit anyway and
furthermore it is signed which means most people have to look up C standard
to remember how right shift is (un)defined if it would overflow ;). So this
does not really make the code any more readable. Rather on contrary...
Honza
>
> >
> > > - iomap->offset = (u64)first_block << blkbits;
> > > + iomap->offset = (loff_t)first_block << blkbits;
> >
>
> ---
> Cheers,
> Huaisheng
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
WARNING: multiple messages have this Message-ID (diff)
From: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
To: Huaisheng Ye <yehs2007-ytc+IHgoah0@public.gmane.org>
Cc: linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org,
chengnt-6jq1YtArVR3QT0dZR+AlfA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org,
"\"Al Viro\""
<viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
jack-IBi9RG/b67k@public.gmane.org,
linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 2/3] fs/ext2/inode: Fix a type cast error for fsdax
Date: Mon, 2 Jul 2018 09:55:43 +0200 [thread overview]
Message-ID: <20180702075543.k7y73aj3s3gp4ptz@quack2.suse.cz> (raw)
In-Reply-To: <16459a9432e.10c419704327.5268154349116077352-ytc+IHgoah0@public.gmane.org>
On Mon 02-07-18 14:23:42, Huaisheng Ye wrote:
> ---- On Mon, 02 Jul 2018 03:26:00 +0800 Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org> wrote ----
> > On Sun, Jul 01, 2018 at 02:18:47PM +0800, Huaisheng Ye wrote:
> > > From: Huaisheng Ye <yehs1-6jq1YtArVR3QT0dZR+AlfA@public.gmane.org>
> > >
> > > 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?
I think what Al meant is that in the kernel loff_t is 64-bit anyway and
furthermore it is signed which means most people have to look up C standard
to remember how right shift is (un)defined if it would overflow ;). So this
does not really make the code any more readable. Rather on contrary...
Honza
>
> >
> > > - iomap->offset = (u64)first_block << blkbits;
> > > + iomap->offset = (loff_t)first_block << blkbits;
> >
>
> ---
> Cheers,
> Huaisheng
>
>
--
Jan Kara <jack-IBi9RG/b67k@public.gmane.org>
SUSE Labs, CR
next prev parent reply other threads:[~2018-07-02 7:55 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-01 6:18 [PATCH 1/3] drivers/dax/super: Add annotation for ops in struct dax_device Huaisheng Ye
2018-07-01 6:18 ` Huaisheng Ye
2018-07-01 6:18 ` Huaisheng Ye
2018-07-01 6:18 ` [PATCH 2/3] fs/ext2/inode: Fix a type cast error for fsdax Huaisheng Ye
2018-07-01 6:18 ` Huaisheng Ye
2018-07-01 6:18 ` Huaisheng Ye
2018-07-01 19:26 ` Al Viro
2018-07-01 19:26 ` Al Viro
2018-07-01 19:26 ` Al Viro
2018-07-02 6:23 ` Huaisheng Ye
2018-07-02 6:23 ` Huaisheng Ye
2018-07-02 6:23 ` Huaisheng Ye
2018-07-02 7:55 ` Jan Kara [this message]
2018-07-02 7:55 ` Jan Kara
2018-07-02 7:55 ` Jan Kara
2018-07-01 6:18 ` [PATCH 3/3] fs/ext2/inode: Optimize the condition for iomap_begin Huaisheng Ye
2018-07-01 6:18 ` Huaisheng Ye
2018-07-01 6:18 ` Huaisheng Ye
2018-07-02 7:57 ` Jan Kara
2018-07-02 7:57 ` Jan Kara
2018-07-02 7:57 ` Jan Kara
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