Re: git guidance

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Nov 29, 2007, 16:19 UTC
Message-ID: <alpine.LFD.0.9999.0711290810170.8458@woody.linux-foundation.org>
In-Reply-To: <20071129105220.v40i22q4gw4cgoso@intranet.digizenstudio.com>

On Thu, 29 Nov 2007, Jing Xue wrote:

Show 7 quoted lines

> 
> By the way, the only SCM I have worked with that tries to mount its
> repository (or a view on top of it) as a file system is ClearCase with
> its dynamic views. And, between the buggy file system implementation,
> the intrusion on workflow, and the lack of scalability, at least in
> the organization I worked for, it turned out to be a horrible,
> horrible, horrible idea.

Doing a read-only mount setup tends to be pretty easy, but it's largely pointless except for specialty uses. Ie it's obviously not useful for actual *development*, but it can be useful for some other cases.

For example, a read-only revctrl filesystem can be a _very_ useful thing for test-farms, where you may have hundreds of clients that run tests on possibly different versions at the same time. In situations like that, the read-only mount can actually often be done as a user-space NFS server on some machine.

The advantage is that you don't need to export close to infinite amounts of versions from a "real" filesystem, or make the clients have their own copies. And if you do it as a user-space NFS server (or samba, for that matter), it's even portable, unlike many other approaches. The read-only part also makes 99% of all the complexity go away, and it turns out to be a fairly easy exercise to do.

So I don't think the filesystem approach is _wrong_ per se. But yes, doing it read-write is almost invariably a big mistake. On operatign systems that support a "union mount" approach, it's likely much better to have a read-only revctl thing, and then over-mount a regular filesystem on top of it.

Trying to make it read-write from the revctl engine standpoint is almost certainly totally insane.

				Linus