From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <aliguori@us.ibm.com>
Subject: Re: [Xen-changelog] Make xenstored reopen its trace
 file on SIGHUP. This allows one to rotate the
Date: Mon, 07 Nov 2005 11:15:34 -0600
Message-ID: <436F8BB6.1090207@us.ibm.com>
References: <E1EZ6jH-0002pi-4u@xenbits.xensource.com>
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Cc: Ewan Mellor <ewan@xensource.com>
List-Id: xen-devel@lists.xenproject.org

Xen patchbot -unstable wrote:

> 
>+void reopen_log()
>+{
>+	if (!tracefile)
>+		return;
>+
>+	if (tracefd > 0)
>+		close(tracefd);
>+	tracefd = open(tracefile, O_WRONLY|O_CREAT|O_APPEND, 0600);
>+	if (tracefd < 0) {
>+		perror("Could not open tracefile");
>+		return;
>+	}
>+	write(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.

Regards,

Anthony Liguori

> static bool write_messages(struct connection *conn)
> {
> 	int ret;
>@@ -1498,11 +1514,7 @@
> 			outputpid = true;
> 			break;
> 		case 'T':
>-			tracefd = open(optarg, O_WRONLY|O_CREAT|O_APPEND, 0600);
>-			if (tracefd < 0)
>-				barf_perror("Could not open tracefile %s",
>-					    optarg);
>-                        write(tracefd, "\n***\n", strlen("\n***\n"));
>+			tracefile = optarg;
> 			break;
> 		case 'V':
> 			verbose = true;
>@@ -1511,6 +1523,8 @@
> 	}
> 	if (optind != argc)
> 		barf("%s: No arguments desired", argv[0]);
>+
>+	reopen_log();
> 
> 	if (dofork) {
> 		openlog("xenstored", 0, LOG_DAEMON);
>@@ -1577,6 +1591,8 @@
> 		close(STDOUT_FILENO);
> 		close(STDERR_FILENO);
> 	}
>+
>+	signal(SIGHUP, reopen_log);
> 
> #ifdef TESTING
> 	signal(SIGUSR1, stop_failtest);
>
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>  
>