From mboxrd@z Thu Jan  1 00:00:00 1970
From: Hollis Blanchard <hollisb@us.ibm.com>
Subject: Re: Re: [Xen-changelog] Make xenstored reopen its trace
	file on SIGHUP. This allows one to rotate the
Date: Mon, 7 Nov 2005 11:24:02 -0600
Message-ID: <200511071124.02430.hollisb@us.ibm.com>
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Cc: Ewan Mellor <ewan@xensource.com>
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On Monday 07 November 2005 11:15, Anthony Liguori wrote:
> >+void reopen_log()
> >+{
> >+=A0=A0=A0=A0=A0=A0if (!tracefile)
> >+=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0return;
> >+
> >+=A0=A0=A0=A0=A0=A0if (tracefd > 0)
> >+=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0close(tracefd);
> >+=A0=A0=A0=A0=A0=A0tracefd =3D open(tracefile, O_WRONLY|O_CREAT|O_APPEND=
, 0600);
> >+=A0=A0=A0=A0=A0=A0if (tracefd < 0) {
> >+=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0perror("Could not open tracef=
ile");
> >+=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0return;
> >+=A0=A0=A0=A0=A0=A0}
> >+=A0=A0=A0=A0=A0=A0write(tracefd, "\n***\n", strlen("\n***\n"));
> >+}
>
> perror and strlen are not safe to call from a signal handler.
>
> I suggest just removing the perror call altogether and replacing strlen
> with sizeof() - 1.

I'm really not sure how strlen could be non-threadsafe. I don't care if it'=
s=20
not in your list; your list doesn't include strtok_r either, and that is=20
explicitly thread-safe. :-P

However, in addition to perror, another thread could try to use tracefd=20
between the close and the open. You'd probably want to do something like:
	oldfd =3D tracefd;
	newfd =3D open();
	if (newfd < 0) {
		...
	}
	tracefd =3D newfd;
	close(oldfd);

=46inally, you really should do error-checking on close(). See the close(2)=
 man=20
page...

=2D-=20
Hollis Blanchard
IBM Linux Technology Center