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

From: Junio C Hamano <junkio@cox.net>
Date: Aug 31, 2006, 21:31 UTC
Message-ID: <7vsljc8udx.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <Pine.LNX.4.64.0608311409470.27779@g5.osdl.org>

Linus Torvalds <torvalds@osdl.org> writes:

Show 7 quoted lines

> That way, if you want to do the fd thing, you can always just do
>
> 	GIT_TRACE=/proc/self/fd/9 make test 9>/var/tmp/trace.log
>
> although I really don't know how well that works across a fork/exec that 
> may or may not be closing the file descriptor (I think it's much simpler 
> and more obvious to just give the filename directly).

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).

Process A has fd=9 opened to /var/tmp/trace.log and forks process B.

(1) process B execs something else, and just writes into fd=9

or

(2) process B execs something else, perhaps after closing fd=9,
    and the exec'ed image opens /var/tmp/trace.log with
    "O_APPEND|O_CREAT" and gets a fd; it writes into this fd.

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