Re: 6543fa5a5c47 - main - dumpon: warn if the configured netdump link is down

On 5/16/22 13:22, Ravi Pokala wrote:
> -----Original Message-----
> From: <owner-src-committers@freebsd.org> on behalf of Mitchell Horne <mhorne@FreeBSD.org>
> Date: 2022-05-14, Saturday at 06:28
> To: <src-committers@FreeBSD.org>, <dev-commits-src-all@FreeBSD.org>, <dev-commits-src-main@FreeBSD.org>
> Subject: git: 6543fa5a5c47 - main - dumpon: warn if the configured netdump link is down
> 
>      The branch main has been updated by mhorne:
> 
>      URL: https://cgit.FreeBSD.org/src/commit/?id=6543fa5a5c47cfbea92586f0994431fc8ba09f6a
> 
>      commit 6543fa5a5c47cfbea92586f0994431fc8ba09f6a
>      Author:     Mitchell Horne <mhorne@FreeBSD.org>
>      AuthorDate: 2022-05-14 13:25:21 +0000
>      Commit:     Mitchell Horne <mhorne@FreeBSD.org>
>      CommitDate: 2022-05-14 13:27:54 +0000
> 
>          dumpon: warn if the configured netdump link is down
> 
>          Previously we expected the DIOCSKERNELDUMP ioctl to return ENXIO if the
>          interface was down, but it does not actually do this. Grab the link
>          status using getifaddrs(3) instead, and downgrade this case from an
>          error to a warning; the user might bring the link back up at a later
>          time.
> 
> Testing whether or not a given link is up sounds like something that should be in libifconfig. If it's there, wouldn't it be better to use that rather than creating check_link_status()? And if it's not there, shouldn't it be?
> 
> Thanks,
> 
> Ravi (rpokala@)
> 

I did look for something like this in libifconfig while making this 
change but did not find anything useful there currently. Certainly it 
would make sense to have this kind of helper, even something that just 
returns the struct ifaddrs * corresponding to a given ifname.

However, this change was already a bonus enhancement to complement 
38a36057ae56, so I won't be the one to lead the charge of generalizing 
this pattern into libifconfig.

Cheers,
Mitchell

>          Reviewed by:    cem
>          MFC after:      1 week
>          Differential Revision:  https://reviews.freebsd.org/D35196
>      ---
>       sbin/dumpon/dumpon.c | 27 +++++++++++++++++++++++----
>       1 file changed, 23 insertions(+), 4 deletions(-)
> 
>      diff --git a/sbin/dumpon/dumpon.c b/sbin/dumpon/dumpon.c
>      index 7d8f81d5eaaf..626350427595 100644
>      --- a/sbin/dumpon/dumpon.c
>      +++ b/sbin/dumpon/dumpon.c
>      @@ -186,6 +186,25 @@ find_gateway(const char *ifname)
>       	return (ret);
>       }
> 
>      +static void
>      +check_link_status(const char *ifname)
>      +{
>      +	struct ifaddrs *ifap, *ifa;
>      +
>      +	if (getifaddrs(&ifap) != 0)
>      +		err(EX_OSERR, "getifaddrs");
>      +
>      +	for (ifa = ifap; ifa != NULL; ifa = ifa->ifa_next) {
>      +		if (strcmp(ifname, ifa->ifa_name) != 0)
>      +			continue;
>      +		if ((ifa->ifa_flags & IFF_UP) == 0) {
>      +			warnx("warning: %s's link is down", ifname);
>      +		}
>      +		break;
>      +	}
>      +	freeifaddrs(ifap);
>      +}
>      +
>       static void
>       check_size(int fd, const char *fn)
>       {
>      @@ -659,6 +678,9 @@ main(int argc, char *argv[])
>       		else
>       			error = errno;
>       	}
>      +	/* Emit a warning if the user configured a downed interface. */
>      +	if (error == 0 && netdump)
>      +		check_link_status(kdap->kda_iface);
>       	explicit_bzero(kdap->kda_encryptedkey, kdap->kda_encryptedkeysize);
>       	free(kdap->kda_encryptedkey);
>       	explicit_bzero(kdap, sizeof(*kdap));
>      @@ -669,10 +691,7 @@ main(int argc, char *argv[])
>       			 * errors, especially as users don't have any great
>       			 * discoverability into which NICs support netdump.
>       			 */
>      -			if (error == ENXIO)
>      -				errx(EX_OSERR, "Unable to configure netdump "
>      -				    "because the interface's link is down.");
>      -			else if (error == ENODEV)
>      +			if (error == ENODEV)
>       				errx(EX_OSERR, "Unable to configure netdump "
>       				    "because the interface driver does not yet "
>       				    "support netdump.");
> 
>