Re: [PATCH] Trace into open fd and refactor tracing code.

From: Linus Torvalds <torvalds@osdl.org>
Date: Aug 31, 2006, 21:49 UTC
Message-ID: <Pine.LNX.4.64.0608311444200.27779@g5.osdl.org>
In-Reply-To: <7vsljc8udx.fsf@assigned-by-dhcp.cox.net>

On Thu, 31 Aug 2006, Junio C Hamano wrote:

> 
> Actually it was me who suggested the use of fd directly, along
> with trying to do one message in a single write (i.e. not doing
> stdio as much as possible).

I definitely agree with the "one message in a single write" thing.

That's in fact required to make sure that O_APPEND works properly (ie that you don't have potentially different processes mixing output)

> I somehow felt there would be less interference between writes
> issued by process A and process B, but probably I am mistaken.

The atomicity guarantees are the same regardless of whether you do a separate open(), the only thing that matters is that you do want to try to do messages with a single "write()" call, and that you use O_APPEND. That should guarantee that you get good behaviour.

Without O_APPEND, you would obviously have to share one single file descriptor, because otherwise people will just be writing all over each other.

			Linus