file system change notifications

[Mateusz Guzik]

On Wed, Mar 11, 2015 at 11:11:14PM +0100, Oliver Pinter wrote:
> Take a look at dazuko kernel module. Probably you should forward port
> them, because they are obsoleted.
> 

I checked the module out of curiosity. Their approach was to wrap various
syscalls and work from there. This is used to be the common approach
several years back it has a lot of shortcomings, complete lack of
reliability being the biggest one.

As for better implementation: current namecache does not guarantee name
resolution (even if name was entered) and not all names end up in the
cache in the first place.

Lack of reliability comes from the fact that the cache does not pin
vnodes in any way.

The cache is also protected with one sx lock and requires users to get
and drop refs during lookups.

As such, I would say that the best course of action is implementing new
cache instead of hacking current implementatin.

Then something could be made on top of that.

> On Wed, Mar 11, 2015 at 10:54 PM, Kim Shrier <kim at westryn.net> wrote:
> > On Mar 11, 2015, at 1:14 PM, Ivan Krivonos <int0dster at gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> Have not read this paper, but why just don`t kqueue() ?
> >>
> >
> > Apparently, you have to have a file descriptor for every file you want to
> > monitor, if I read things right.  This is prohibitive with 100,000+ files.
> > It also means that you cannot unmount a file system if you are monitoring
> > any files in it, since the file system is considered busy.
> >
> > Kim
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-- 
Mateusz Guzik <mjguzik gmail.com>