[Devel] Re: [PATCH 2/2] Add checkpoint/restart support for epoll files.

[Matt Helsley]

On Fri, Oct 02, 2009 at 05:22:16PM -0400, Oren Laadan wrote:
> 
> 
> Matt Helsley wrote:
> 
> [...]
> 
> >>>> s/ckpt_obj_collect/ckpt_collect_file/
> >>> OK. Seems like we might recurse here though if the file is an epoll
> >>> file and there's a cycle in the epoll sets (e.g. epoll set A includes the fd
> >>> for epoll set B, epoll set B includes the fd for epoll set A).
> >>> So I think I'll do:
> >> I doubt if an epoll file can epoll an epoll file ...
> >> (eg. see line 1265 in fs/eventpoll.c)
> > 
> > I am certain it can. The testcase I have proves it and the man page mentions
> > it too. Since it has a poll op I believe it can be epoll'd (line 691 of
> > fs/eventpoll.c).
> > 
> > I haven't double checked, but I believe the line you cited just prevents the
> > epoll set from including its own fd.
> 
> Duh ... you are totally correct. Sorry for the noise.

No problem -- whoever's right or wrong, it's always good to have folks
who are trying to help check these things.

> 
> [...]
> 
> >>> Otherwise I wonder if it would be better to join the prefmt and fmt
> >>> strings by just defining our own, new, conversion specifiers.
> >>>
> >> Thought about it, but that would limit us in the conversion specifiers
> >> that we can use, because many are used by printf already. Perhaps one
> >> way to do it is use
> >> 	"%Zxyz"
> >> where "%Z" tells the following letters indicate a ckpt_write_err()
> >> format, and then "xyz" are the letters from the current @prefmt.
> > 
> > Would %( work better? The ( suggests that there's more to it.
> 
> Sounds cool. Care to work out the details with a patch ?

I've got enough on my plate for now -- I've got to update and send out
the next epoll patch. I've got the user-cr kernel header patches to send
out. And I'm looking at what to do for unlinked files, inotify, eventfd,
timerfd, and signalfd (all but the first two should be even simpler than
epoll).

Cheers,
	-Matt Helsley
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