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

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Message-ID: <Yg0421B10PPwunI+@kroah.com>
Date:   Wed, 16 Feb 2022 18:48:11 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     JeffleXu <jefflexu@...ux.alibaba.com>
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 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 :(

thanks,

greg k-h