Re: [PATCH v3 2/9] pcap: add pcap_iov()

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

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On Sat, Feb 17, 2024 at 04:07:18PM +0100, Laurent Vivier wrote:
> Introduce a new function pcap_iov() to capture packet desribed by an IO
> vector.
> 
> Move packet header writing to to pcap_header() and use it in
> pcap_frame() and pcap_iov().
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

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

> ---
> 
> Notes:
>     v3:
>       - update rational
>       - update comment
>       - use strerror(errno)
>       - use size_t for io vector length
>     
>     v2:
>       - introduce pcap_header(), a common helper to write
>         packet header
>       - use writev() rather than write() in a loop
>       - add functions comment
> 
>  pcap.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
>  pcap.h |  1 +
>  2 files changed, 56 insertions(+), 7 deletions(-)
> 
> diff --git a/pcap.c b/pcap.c
> index 501d52d4992b..4e213eea8113 100644
> --- a/pcap.c
> +++ b/pcap.c
> @@ -20,6 +20,7 @@
>  #include <sys/time.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
> +#include <sys/uio.h>
>  #include <fcntl.h>
>  #include <time.h>
>  #include <errno.h>
> @@ -31,6 +32,7 @@
>  #include "util.h"
>  #include "passt.h"
>  #include "log.h"
> +#include "iov.h"
>  
>  #define PCAP_VERSION_MINOR 4
>  
> @@ -65,6 +67,28 @@ struct pcap_pkthdr {
>  	uint32_t len;
>  };
>  
> +/*
> + * pcap_header() - Write a pcap packet header to pcap file
> + *
> + * @len:       Length of the packet data.
> + * @tv:        Timestamp for the packet.
> + *
> + * Return: -1 in case of error, otherwise, 0 to indicate success.
> + */
> +static int pcap_header(size_t len, const struct timeval *tv)
> +{
> +	struct pcap_pkthdr h;
> +
> +	h.tv_sec = tv->tv_sec;
> +	h.tv_usec = tv->tv_usec;
> +	h.caplen = h.len = len;
> +
> +	if (write(pcap_fd, &h, sizeof(h)) < 0)
> +		return -1;
> +
> +	return 0;
> +}
> +
>  /**
>   * pcap_frame() - Capture a single frame to pcap file with given timestamp
>   * @pkt:	Pointer to data buffer, including L2 headers
> @@ -75,13 +99,7 @@ struct pcap_pkthdr {
>   */
>  static int pcap_frame(const char *pkt, size_t len, const struct timeval *tv)
>  {
> -	struct pcap_pkthdr h;
> -
> -	h.tv_sec = tv->tv_sec;
> -	h.tv_usec = tv->tv_usec;
> -	h.caplen = h.len = len;
> -
> -	if (write(pcap_fd, &h, sizeof(h)) < 0 || write(pcap_fd, pkt, len) < 0)
> +	if (pcap_header(len, tv) < 0 || write(pcap_fd, pkt, len) < 0)
>  		return -errno;
>  
>  	return 0;
> @@ -130,6 +148,36 @@ void pcap_multiple(const struct iovec *iov, unsigned int n, size_t offset)
>  	}
>  }
>  
> +/*
> + * pcap_iov - Write packet data described by a scatter/gather I/O vector (iov)
> + *             to a pcap file descriptor (pcap_fd).
> + *
> + * @iov:       Pointer to the array of struct iovec describing the scatter/gather
> + *             I/O vector containing packet data to write, including L2 header
> + * @n:         Number of elements in the iov array.
> + */
> +void pcap_iov(const struct iovec *iov, size_t n)
> +{
> +	struct timeval tv;
> +	size_t len;
> +
> +	if (pcap_fd == -1)
> +		return;
> +
> +	gettimeofday(&tv, NULL);
> +
> +	len = iov_size(iov, n);
> +
> +	if (pcap_header(len, &tv) < 0) {
> +		debug("Cannot write pcap header");
> +		return;
> +	}
> +
> +	if (writev(pcap_fd, iov, n) < 0)
> +		debug("Cannot log packet using writev(): %s\n",
> +		      strerror(errno));
> +}
> +
>  /**
>   * pcap_init() - Initialise pcap file
>   * @c:		Execution context
> diff --git a/pcap.h b/pcap.h
> index da5a7e846b72..4950f617f4c8 100644
> --- a/pcap.h
> +++ b/pcap.h
> @@ -8,6 +8,7 @@
>  
>  void pcap(const char *pkt, size_t len);
>  void pcap_multiple(const struct iovec *iov, unsigned int n, size_t offset);
> +void pcap_iov(const struct iovec *iov, size_t n);
>  void pcap_init(struct ctx *c);
>  
>  #endif /* PCAP_H */

-- 
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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