Re: [dpdk-dev] [PATCH v5 4/5] vhost: eventfd_link: replace copy-pasted sys_close

["Xie, Huawei" <huawei.xie@intel.com>]

On 7/10/2015 11:50 PM, Thomas Monjalon wrote:
> 2015-07-10 15:42, Xie, Huawei:
>> Don't know why previous mail get messed.
> Same problem with this one.
> It's maybe because you send HTML mail which is wrongly translated in plain text.
Have something to to with Pavel? :). I remember the format usually get
messed  when i reply to his mail.
Anyway, I changed delivery format in Thunderbird from "Auto detect" to
"Plain text only".
>  
>> On 7/10/2015 10:50 PM, Pavel Boldin wrote:
>> Xie,
>>
>> Regarding the patches:
>> 1. The replaced code in fourth patch is checked to be a copy-paste of the `sys_close` syscall.
>>
>> sys_close does extra cleanup than the replaced coe. My concern is, for example, sys_close will mark the fd as next-to-be-allocated fd. Will there be issue when we allocate a new fd, because it will be allocated starting from the value of next-to-be-allocted-fd? I think kernel willn't blindly use that value, but not sure.
>>
>> 2. It is not uncommon for the applications to close FD making it allocated for a different file. In our particular case the file is closed in the *source* process and *added* to a target process, so matching fds should not be the problem.
>>
>> Yes, that is exactly what the old code does.
>> 3. There is an implementation of the exact same thing in the SCM_RIGHTS [1] that can be used as the reference code.
>>
>> I did a rough check. Maybe i miss something. I see it calls fd_install on a newly allocated fd. That is exactly what i want to replace the current  code with.
>> Currently we allcoate eventfd in user space and install a new file onto it through fd_install. Actually we don't need to allocate the eventfd in user space at all, what we should do is allocate a new fd in kernel, and install the file onto it.
>>
>> new_fd = get_unused_fd_flags(...)
>> fd_install(new_fd, get_file(fp[i])
>>
>> /huawei
>>
>> [1] https://github.com/torvalds/linux/blob/master/net/core/scm.c#L248
>>
>> Pavel
>>
>> On Fri, Jul 10, 2015 at 5:27 PM, Xie, Huawei <huawei.xie@intel.com<mailto:huawei.xie@intel.com>> wrote:
>> On 6/17/2015 11:24 PM, Thomas Monjalon wrote:
>>> 2015-05-07 06:54, Xie, Huawei:
>>>> On 4/16/2015 7:48 PM, Pavel Boldin wrote:
>>>>> +   /* Closing the source_fd */
>>>>> +   ret = sys_close(eventfd_copy.source_fd);
>>>> Pavel:
>>>> Here we close the fd and re-install a new file on this fd later.
>>>> sys_close does all cleanup.
>>>> But, for instance, if we allocate new fd later, normally it will reuse
>>>> the just freed fds by sys_close, is there issue here?
>>> Pavel, Huawei,
>>> Could we come to a conclusion on this patch series please?
>> For the previous 3 patches, i am OK except that i don't think inline is
>> needed explicitly for non-performance critical function.
>> For this patch, didn't check the fs code.
>>
>>>
>>
>>
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