linux-kernel - Re: [PATCH v4 05/23] cachefiles: introduce new devnode for on-demand read mode

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Date:   Thu, 17 Feb 2022 09:49:26 +0800
From:   JeffleXu <jefflexu@...ux.alibaba.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     dhowells@...hat.com, linux-cachefs@...hat.com, xiang@...nel.org,
        chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        torvalds@...ux-foundation.org, willy@...radead.org,
        linux-fsdevel@...r.kernel.org, joseph.qi@...ux.alibaba.com,
        bo.liu@...ux.alibaba.com, tao.peng@...ux.alibaba.com,
        gerry@...ux.alibaba.com, eguan@...ux.alibaba.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 05/23] cachefiles: introduce new devnode for on-demand
 read mode



On 2/17/22 1:48 AM, Greg KH wrote:
> On Wed, Feb 16, 2022 at 08:49:35PM +0800, JeffleXu wrote:
>>>> +struct cachefiles_req_in {
>>>> +	uint64_t id;
>>>> +	uint64_t off;
>>>> +	uint64_t len;
>>>
>>> For structures that cross the user/kernel boundry, you have to use the
>>> correct types.  For this it would be __u64.
>>
>> OK I will change to __xx style in the next version.
>>
>> By the way, I can't understand the disadvantage of uintxx_t style.
> 
> The "uint*" types are not valid kernel types.  They are userspace types
> and do not transfer properly in all arches and situations when crossing
> the user/kernel boundry.  They are also in a different C "namespace", so
> should not even be used in kernel code, although a lot of people do
> because they are used to writing userspace C code :(

OK. "uint*" types are defined in ISO C library, while it seems that
linux kernel doesn't expect any C library [1].

[1] https://kernelnewbies.org/FAQ/LibraryFunctionsInKernel

Thanks for explaining it.

-- 
Thanks,
Jeffle