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

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

Don't know why previous mail get messed.

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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