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SubjectRe: [PATCH] kernel/sysctl: return -EINVAL if write invalid val to ulong type sysctl
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On 2016/12/1 5:33, Andrew Morton wrote:
> On Wed, 30 Nov 2016 18:30:52 +0800 Yisheng Xie <xieyisheng1@huawei.com> wrote:
>
>> I tried to echo an invalid value to an unsigned long type sysctl on
>> 4.9.0-rc6:
>> linux:~# cat /proc/sys/vm/user_reserve_kbytes
>> 131072
>> linux:~# echo -1 > /proc/sys/vm/user_reserve_kbytes
>> linux:~# cat /proc/sys/vm/user_reserve_kbytes
>> 131072
>>
>> The echo operation got error and the value do not write to
>> user_reserve_kbytes, however, user do not know it until checking
>> the value again.
>>
>> This patch return -EINVAL when write an invalid value to unsigned
>> long type sysctl to make user know what happened without
>> checking its value once more, just as what proc_douintvec do.
>
> hmpf.
>
> # echo 18446744073709551615 > /proc/sys/vm/user_reserve_kbytes
> # cat /proc/sys/vm/user_reserve_kbytes
> 18446744073709551615
>
> I think that when taking in an unsigned long the kernel should simply
> treat -1 as 0xffffffff (or 0xffffffffffffffff). It's natural and
> normal and everyone knows what it means?
>
Hi Andrew,
Thank you for your reply.
Do you means it should be like this:
# echo -1 > /proc/sys/vm/user_reserve_kbytes
# cat /proc/sys/vm/user_reserve_kbytes
18446744073709551615

I looks ok to me, however, I not sure whether other code in the kernel
will also use its complement if user write a negative number for an
unsigned long. Does anyone have other opinion ?

Thanks
Yisheng Xie.

>
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>
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>

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