Re: [PATCH] pcap: Use clock_gettime() instead of gettimeofday()

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Mar 12, 2024 at 08:01:20PM +0100, Stefano Brivio wrote:
> POSIX.1-2008 declared gettimeofday() as obsolete, but I'm a dinosaur.
> 
> Usually, C libraries translate that to the clock_gettime() system
> call anyway, but this doesn't happen in Jon's environment, and,
> there, seccomp happily kills pasta(1) when started with --pcap,
> because we didn't add gettimeofday() to our seccomp profiles.
> 
> Use clock_gettime() instead.
> 
> Reported-by: Jon Maloy <jmaloy@redhat.com>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  pcap.c | 26 +++++++++++++-------------
>  util.h |  1 +
>  2 files changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/pcap.c b/pcap.c
> index a0f01ad..45bbfcd 100644
> --- a/pcap.c
> +++ b/pcap.c
> @@ -72,17 +72,17 @@ struct pcap_pkthdr {
>   * @iov:	IO vector containing frame (with L2 headers and tap headers)
>   * @iovcnt:	Number of buffers (@iov entries) in frame
>   * @offset:	Byte offset of the L2 headers within @iov
> - * @tv:		Timestamp
> + * @now:	Timestamp
>   *
>   * Returns: 0 on success, -errno on error writing to the file
>   */
>  static void pcap_frame(const struct iovec *iov, size_t iovcnt,
> -		       size_t offset, const struct timeval *tv)
> +		       size_t offset, const struct timespec *now)
>  {
>  	size_t len = iov_size(iov, iovcnt) - offset;
>  	struct pcap_pkthdr h = {
> -		.tv_sec = tv->tv_sec,
> -		.tv_usec = tv->tv_usec,
> +		.tv_sec = now->tv_sec,
> +		.tv_usec = DIV_ROUND_CLOSEST(now->tv_nsec, 1000),
>  		.caplen = len,
>  		.len = len
>  	};
> @@ -103,13 +103,13 @@ static void pcap_frame(const struct iovec *iov, size_t iovcnt,
>  void pcap(const char *pkt, size_t len)
>  {
>  	struct iovec iov = { (char *)pkt, len };
> -	struct timeval tv;
> +	struct timespec now;
>  
>  	if (pcap_fd == -1)
>  		return;
>  
> -	gettimeofday(&tv, NULL);
> -	pcap_frame(&iov, 1, 0, &tv);
> +	clock_gettime(CLOCK_REALTIME, &now);
> +	pcap_frame(&iov, 1, 0, &now);
>  }
>  
>  /**
> @@ -122,16 +122,16 @@ void pcap(const char *pkt, size_t len)
>  void pcap_multiple(const struct iovec *iov, size_t frame_parts, unsigned int n,
>  		   size_t offset)
>  {
> -	struct timeval tv;
> +	struct timespec now;
>  	unsigned int i;
>  
>  	if (pcap_fd == -1)
>  		return;
>  
> -	gettimeofday(&tv, NULL);
> +	clock_gettime(CLOCK_REALTIME, &now);
>  
>  	for (i = 0; i < n; i++)
> -		pcap_frame(iov + i * frame_parts, frame_parts, offset, &tv);
> +		pcap_frame(iov + i * frame_parts, frame_parts, offset, &now);
>  }
>  
>  /*
> @@ -145,13 +145,13 @@ void pcap_multiple(const struct iovec *iov, size_t frame_parts, unsigned int n,
>  /* cppcheck-suppress unusedFunction */
>  void pcap_iov(const struct iovec *iov, size_t iovcnt)
>  {
> -	struct timeval tv;
> +	struct timespec now;
>  
>  	if (pcap_fd == -1)
>  		return;
>  
> -	gettimeofday(&tv, NULL);
> -	pcap_frame(iov, iovcnt, 0, &tv);
> +	clock_gettime(CLOCK_REALTIME, &now);
> +	pcap_frame(iov, iovcnt, 0, &now);
>  }
>  
>  /**
> diff --git a/util.h b/util.h
> index 25e54a7..48f3560 100644
> --- a/util.h
> +++ b/util.h
> @@ -40,6 +40,7 @@
>  #endif
>  
>  #define DIV_ROUND_UP(n, d)	(((n) + (d) - 1) / (d))
> +#define DIV_ROUND_CLOSEST(n, d)	(((n) + (d) / 2) / (d))
>  #define ROUND_DOWN(x, y)	((x) & ~((y) - 1))
>  #define ROUND_UP(x, y)		(((x) + (y) - 1) & ~((y) - 1))
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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