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    SubjectRe: [RFC/PATCH] inotify -- a dnotify replacement
    On Mon, 2004-05-10 at 22:47, Chris Wedgwood wrote:
    > On Mon, May 10, 2004 at 06:17:40PM -0400, John McCutchan wrote:
    > > According to everyone who uses dnotify it is.
    > I don't buy that. I have used dnotify and signals where not an issue.
    > Why is this an issue for others?

    Signals cause a big performance penalty when you are receiving a lot of
    them. Signals interrupt your program, switch the signal handler and then
    restarts your program. And signals in multi-threaded programs is a pain
    as well. Signals just are not suitable for receiving lots of messages

    > > > 3) dnotify cannot easily watch changes for a directory hierarchy
    > > People don't seem to really care about this one. Alexander Larsson
    > > has said he doesn't care about it. It might be nice to add in the
    > > future.
    > I don't know who that is and why it matters.
    > Without being able to watch a hierarchy, I'm not sure inotify buys
    > anything that we can't get from dnotify right now though. It's also
    > more complex.

    Inotify will support watching a hierarchy. The reason it was not
    implemented yet is because the one app that I really care about is
    nautilus and the maintainer of it says he doesn't care.

    The big feature that inotify is trying to provide is not having to keep
    a file open (So that unmounting is not affected). I asked for some
    guidance from people more familiar with the kernel so that I can
    implement this feature, it requires changes made to the inode cache, and
    how unmounting is done.

    > > The idea is to encourage use of a user-space daemon that will
    > > multiplex all requests, so if 5 people want to watch /somedir the
    > > daemon will only use one watcher in the kernel. The number might be
    > > too low, but its easily upped.
    > If you are to use a daemon for this, why no use dnotify?

    Because of the problems that dnotify has, as well if people would prefer
    to just use a direct interface, those #defines can be upped. Its very
    easy to play with the limits on the number of watchers. I am not sure
    what kind of impact this will have on the kernel resources, so I wanted
    to keep it small.

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