# Re: \[RFC 1/3\] procfs: fdinfo -- Extend information about epoll target files

- From: Cyrill Gorcunov \<hidden\>
- Date: 2017-02-22 07:54:38 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2017/02/117415
- Thread: https://ratatoskr.run/linux-fsdevel/2017/02/117419/t.md

```text
On Wed, Feb 22, 2017 at 10:44:07AM +0300, Pavel Emelyanov wrote:
> On 02/21/2017 10:16 PM, Cyrill Gorcunov wrote:
> > On Tue, Feb 21, 2017 at 10:41:12AM -0800, Andy Lutomirski wrote:
> >>> Thus lets add file position, inode and device number where
> >>> this target lays. This three fields can be used as a primary
> >>> key for sorting, and together with kcmp help CRIU can find
> >>> out an exact file target (from the whole set of processes
> >>> being checkpointed).
> >>
> >> I have no problem with this, but I'm wondering whether kcmp's ordered
> >> comparisons could also be used for this purpose.
> > 
> > Yes it can, but it would increas number of kcmp calls signisicantly.
> 
> Actually it shouldn't. If you extend the kcmp argument to accept the
> epollfd:epollslot pair, this would be effectively the same as if you
> had all your epoll-ed files injected into your fdtable with "strange"
> fd numbers. We already have two-level rbtree for this in criu, adding
> extended ("strange") fd to it should be OK.

Nope. Pavel, I guess you forget how we handle file tree in criu currently.
We call for kcmp only if we have to -- when primary key for two entries
is the same.
```