On Thu, Mar 16, 2023 at 11:07:53AM +0000, Jeremy Sowden wrote:
> 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@xxxxxxxxxx>
> ---
> output/pcap/ulogd_output_PCAP.c | 42 ++++++++++++---------------------
> 1 file changed, 15 insertions(+), 27 deletions(-)
>
> diff --git a/output/pcap/ulogd_output_PCAP.c b/output/pcap/ulogd_output_PCAP.c
> index e7798f20c8fc..220fc6dec5fe 100644
> --- a/output/pcap/ulogd_output_PCAP.c
> +++ b/output/pcap/ulogd_output_PCAP.c
> @@ -220,33 +220,21 @@ 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) {
> + if (!write_pcap_header(pi)) {
^^^^
coding style nitpick, it can be fixed before applying it.
> + ulogd_log(ULOGD_ERROR, "can't write pcap header: %s\n",
> + strerror(errno));
> + return -ENOSPC;
> + }
> }
>
> return 0;
> --
> 2.39.2
>
