lkml.org 
[lkml]   [2019]   [Dec]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] fs: introduce is_dot_dotdot helper for cleanup
From
Date
On 12/03/2019 10:39 AM, Darrick J. Wong wrote:
> On Tue, Dec 03, 2019 at 10:07:41AM +0800, Tiezhu Yang wrote:
>> On 12/03/2019 04:03 AM, Matthew Wilcox wrote:
>>> On Mon, Dec 02, 2019 at 06:10:13PM +0800, Tiezhu Yang wrote:
>>>> There exists many similar and duplicate codes to check "." and "..",
>>>> so introduce is_dot_dotdot helper to make the code more clean.
>>> The idea is good. The implementation is, I'm afraid, badly chosen.
>>> Did you benchmark this change at all? In general, you should prefer the
>>> core kernel implementation to that of some less-interesting filesystems.
>>> I measured the performance with the attached test program on my laptop
>>> (Core-i7 Kaby Lake):
>>>
>>> qstr . time_1 0.020531 time_2 0.005786
>>> qstr .. time_1 0.017892 time_2 0.008798
>>> qstr a time_1 0.017633 time_2 0.003634
>>> qstr matthew time_1 0.011820 time_2 0.003605
>>> qstr .a time_1 0.017909 time_2 0.008710
>>> qstr , time_1 0.017631 time_2 0.003619
>>>
>>> The results are quite stable:
>>>
>>> qstr . time_1 0.021137 time_2 0.005780
>>> qstr .. time_1 0.017964 time_2 0.008675
>>> qstr a time_1 0.017899 time_2 0.003654
>>> qstr matthew time_1 0.011821 time_2 0.003620
>>> qstr .a time_1 0.017889 time_2 0.008662
>>> qstr , time_1 0.017764 time_2 0.003613
>>>
>>> Feel free to suggest some different strings we could use for testing.
>>> These seemed like interesting strings to test with. It's always possible
>>> I've messed up something with this benchmark that causes it to not
>>> accurately represent the performance of each algorithm, so please check
>>> that too.
>> [Sorry to resend this email because the mail list server
>> was denied due to it is not plain text.]
>>
>> Hi Matthew,
>>
>> Thanks for your reply and suggestion. I measured the
>> performance with the test program, the following
>> implementation is better for various of test cases:
>>
>> bool is_dot_dotdot(const struct qstr *str)
>> {
>> if (unlikely(str->name[0] == '.')) {
>> if (str->len < 2 || (str->len == 2 && str->name[1] == '.'))
>> return true;
>> }
>>
>> return false;
>> }
>>
>> I will send a v2 patch used with this implementation.
> Can you make it a static inline since it's such a short function?

Thanks for your suggestion, I will make it static inline and
move it to include/linux/fs.h in the v2 patch.

Thanks,

Tiezhu Yang

>
> --D
>
>> Thanks,
>>
>> Tiezhu Yang
>>
>>>> +bool is_dot_dotdot(const struct qstr *str)
>>>> +{
>>>> + if (str->len == 1 && str->name[0] == '.')
>>>> + return true;
>>>> +
>>>> + if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
>>>> + return true;
>>>> +
>>>> + return false;
>>>> +}
>>>> +EXPORT_SYMBOL(is_dot_dotdot);
>>>> diff --git a/fs/namei.c b/fs/namei.c
>>>> index 2dda552..7730a3b 100644
>>>> --- a/fs/namei.c
>>>> +++ b/fs/namei.c
>>>> @@ -2458,10 +2458,8 @@ static int lookup_one_len_common(const char *name, struct dentry *base,
>>>> if (!len)
>>>> return -EACCES;
>>>> - if (unlikely(name[0] == '.')) {
>>>> - if (len < 2 || (len == 2 && name[1] == '.'))
>>>> - return -EACCES;
>>>> - }
>>>> + if (unlikely(is_dot_dotdot(this)))
>>>> + return -EACCES;
>>>> while (len--) {
>>>> unsigned int c = *(const unsigned char *)name++;

\
 
 \ /
  Last update: 2019-12-03 09:35    [W:0.046 / U:9.756 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site