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

Wed, 16 Feb 2022 17:49:58 -0800 


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

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