Duy Nguyen wrote:
> How about this as a start? I did not really check what it does, but it
> does not look complicate enough to pull systemd in.
> http://article.gmane.org/gmane.comp.version-control.git/151934

Clever hack.  I didn't know that there was a switch called
core.ignoreStat which will disable automatic lstat() calls altogether.
 So, Finn advises that we set this switch and run igit instead of git.
 There's a git-inotify-daemon which runs inotifywait with -m forever,
updating a modified_files hash.  When it is sent a TERM from igit
(which is what happens immediately upon execution), it writes all this
collected information about modified files to a named pipe that igit
passes to it.  igit then does a git update-index --assume-unchained
--stdin to read the data from the pipe.  Towards the end of its life,
igit starts up a fresh git-inotify-daemon for future invocations.

Finn notes in the commit message that it offers no speedup, because
.gitignore files in every directory still have to be read.  I think
this is silly: we really should be caching .gitignore, and touching it
only when lstat() reports that the file has changed.

As far as a real implementation that we'd want to merge into git.git
is concerned, I have a few comments:
Running multiple daemons on-the-fly for monitoring filesystem changes
is not elegant at all.  Keeping track of the state of so many loose
daemons is a hard problem: how do we ensure any semblance of
reliability without that?  Systemd is a very big improvement over the
legacy of a hundred loose shell scripts that SysVInit demanded.  It
monitors and babysits daemons; it uses cgroups to even kill
misbehaving daemons.  I can inspect running daemons at any time, and
have a uniform way to start/ stop/ restart them.

Okay, now you're asking me to consider a system-wide daemon
independent of systemd.  It has to run with root privileges so it has
access to everyone's repositories, which means that people have to
trust it beyond doubt.  What does it do?  It has a generic API to
watch filesystem paths and report events over an IP socket.  Do you
think that this will only be useful to git?  Every other version
control system (and presumably many other pieces of software) will
want to use it.  One huge downside I see of making this part of
systemd is Ubuntu.  They've decided not to use systemd for some
unfathomable reason.

Really, the elephant in the room right now seems to be .gitignore.
Until that is fixed, there is really no use of writing this inotify
daemon, no?  Can someone enlighten me on how exactly .gitignore files
are processed?

> Youo may want to search the mail archive. This topic has come up a few
> times before, there may be other similar patches.

The thread you linked me to is a 2010 email, and now it's 2013.  We've
been silent about inotify for three years?

Thanks for your inputs, Duy.
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