Re: [PATCH] fanotify: remove redundant capable(CAP_SYS_ADMIN)s

[Jan Kara <jack@suse.cz>]

On Thu 23-05-19 15:35:18, Christian Brauner wrote:
> So let's say the user tells me:
> - When the "/A/B/C/target" file appears on the host filesystem,
>   please give me access to "target" in the container at a path I tell
>   you.
> What I do right now is listen for the creation of the "target" file.
> But at the time the user gives me instructions to listen for
> "/A/B/C/target" only /A might exist and so I currently add a watch on A/
> and then wait for the creation of B/, then wait for the creation of C/
> and finally for the creation of "target" (Of course, I also need to
> handle B/ and C/ being removed again an recreated and so on.). It would
> be helpful, if I could specify, give me notifications, recursively for
> e.g. A/ without me having to place extra watches on B/ and C/ when they
> appear. Maybe that's out of scope...

I see. But this is going to be painful whatever you do. Consider for
example situation like:

mkdir -p BAR/B/C/
touch BAR/B/C/target
mv BAR A

Or even situation where several renames race so that the end result creates
the name (or does not create it depending on how renames race). And by the
time you decide A/B/C/target exists, it doesn't need to exist anymore.
Honestly I don't see how you want to implement *any* solution in a sane
way. About the most reliable+simple would seem to be stat "A/B/C/target"
once per second as dumb as it is.

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR