pcap: simplify opening of output file

Instead of statting the file, and choosing the mode with which to open
it and whether to write the PCAP header based on the result, always open
it with mode "a" and _then_ stat it.  This simplifies the flow-control
and avoids a race between statting and opening.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 14 insertions, 27 deletions

diff --git a/output/pcap/ulogd_output_PCAP.c b/output/pcap/ulogd_output_PCAP.c
index e7798f2..0daa2c9 100644
--- a/output/pcap/ulogd_output_PCAP.c
+++ b/output/pcap/ulogd_output_PCAP.c
@@ -220,33 +220,20 @@ static int append_create_outfile(struct ulogd_pluginstance *upi)
 {
 	struct pcap_instance *pi = (struct pcap_instance *) &upi->private;
 	char *filename = upi->config_kset->ces[0].u.string;
-	struct stat st_dummy;
-	int exist = 0;
-
-	if (stat(filename, &st_dummy) == 0 && st_dummy.st_size > 0)
-		exist = 1;
-
-	if (!exist) {
-		pi->of = fopen(filename, "w");
-		if (!pi->of) {
-			ulogd_log(ULOGD_ERROR, "can't open pcap file %s: %s\n",
-				  filename,
-				  strerror(errno));
-			return -EPERM;
-		}
-		if (!write_pcap_header(pi)) {
-			ulogd_log(ULOGD_ERROR, "can't write pcap header: %s\n",
-				  strerror(errno));
-			return -ENOSPC;
-		}
-	} else {
-		pi->of = fopen(filename, "a");
-		if (!pi->of) {
-			ulogd_log(ULOGD_ERROR, "can't open pcap file %s: %s\n", 
-				filename,
-				strerror(errno));
-			return -EPERM;
-		}		
+	struct stat st_of;
+
+	pi->of = fopen(filename, "a");
+	if (!pi->of) {
+		ulogd_log(ULOGD_ERROR, "can't open pcap file %s: %s\n",
+			  filename,
+			  strerror(errno));
+		return -EPERM;
+	}
+	if (fstat(fileno(pi->of), &st_of) == 0 && st_of.st_size == 0 &&
+	    !write_pcap_header(pi)) {
+		ulogd_log(ULOGD_ERROR, "can't write pcap header: %s\n",
+			  strerror(errno));
+		return -ENOSPC;
 	}
 
 	return 0;