linux-kernel - Re: [PATCH] fuse: Add ioctl flag for compat ioctl with 64-bit time

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Message-ID: <4dba1140-be46-6c1b-d88a-4cdf4d69cdda@mev.co.uk>
Date:   Wed, 24 Apr 2019 13:33:56 +0100
From:   Ian Abbott <abbotti@....co.uk>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fuse: Add ioctl flag for compat ioctl with 64-bit time_t

On 24/04/2019 11:52, Miklos Szeredi wrote:
> On Tue, Apr 23, 2019 at 5:14 PM Ian Abbott <abbotti@....co.uk> wrote:
>>
>> On 23/04/2019 13:55, Miklos Szeredi wrote:
>>> On Fri, Mar 1, 2019 at 6:08 PM Ian Abbott <abbotti@....co.uk> wrote:
>>>>
>>>> Currently, a CUSE server running on a 64-bit kernel can tell when an
>>>> ioctl request comes from a process running a 32-bit ABI, but cannot tell
>>>> whether the requesting process is using legacy IA32 emulation or x32
>>>> ABI, for example.  In particular, the server does not know the size of
>>>> the client process's `time_t` type.
>>>>
>>>> For 64-bit kernels, the `FUSE_IOCTL_COMPAT` and `FUSE_IOCTL_32BIT` flags
>>>> are currently set in the ioctl input request (`struct fuse_ioctl_in`
>>>> member `flags`) for a 32-bit requesting process.  This patch defines a
>>>> new flag `FUSE_IOCTL_COMPAT_64TIME` and sets it if the 32-bit requesting
>>>> process (running on a 64-bit kernel) uses a 64-bit `time_t` type.
>>>
>>> Hi,
>>>
>>> Thanks for the patch.
>>>
>>> I think it should rather use in_x32_syscall() helper and follow that
>>> naming because there's apparently at least one example in xfs of a
>>> non-time_t related ioctl that varies between the x32 vs ia32.
>>
>> Hi Miklos,
>>
>> It is conceivable that COMPAT_USE_64BIT_TIME could be true for some
>> other arch/ABI (although currently it is only ever set for x86/x32).
>> Should it have separate flags for "compat 64-bit time" and "compat x32"
>> (even though that is currently redundant)?
> 
> No, it should just be a single flag, something like
> FUSE_IOCTL_COMPAT_X32 and the documentation should say that it implies
> 64bit time values.

Okay, since the subject line, description and code will change, I'll 
submit the new patch as a new patch, rather than a "v2".  (I'll mention 
its history below the scissors line.)  Please drop this patch.

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