[PATCH] Don't return error if /sys/class/net/$dev/operstate isn't found

[Laine Stump]

This can happen for alias "interfaces", e.g: "eth0:1" (which aren't
really an interface, but are a deprecated method of adding multiple IP
addresses to a single interface). Since only the base interface
("eth0") is really a device, only it has an entry in /sys/class/net.

It's not important that such interfaces have truly meaningful
information in their <link> element (as we don't really have any truly
meaningful state, and haven't historically provided other status for
alias interfaces (e.g. IP address). What *is* important is that we
don't return an error, as this breaks applications that rely on being
able to get back a successful (if empty) status for any interface
listed.

This resolves the regression with virt-manager described here:

https://bugzilla.redhat.com/show_bug.cgi?id=1185850
---
 src/dutil_linux.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/dutil_linux.c b/src/dutil_linux.c
index 19e36ca..00c378f 100644
--- a/src/dutil_linux.c
+++ b/src/dutil_linux.c
@@ -1081,8 +1081,14 @@ static void add_link_info(struct netcf *ncf,
     xasprintf(&path, "/sys/class/net/%s/operstate", ifname);
     ERR_NOMEM(!path, ncf);
     state = read_file(path, &length);
-    ERR_THROW_STRERROR(!state, ncf, EFILE, "Failed to read %s : %s",
-                       path, errbuf);
+    if (!state) {
+        /* missing operstate is *not* an error. It could be due to an
+         * alias interface, which has not entry in /sys/class/net at
+         * all, for example.
+         */
+        state = strdup("");
+        ERR_NOMEM(!state, ncf);
+    }
     if ((nl = strchr(state, '\n')))
         *nl = 0;
     prop = xmlSetProp(link_node, BAD_CAST "state", BAD_CAST state);

[Eric Blake]

On 01/27/2015 10:48 AM, Laine Stump wrote:
> This can happen for alias "interfaces", e.g: "eth0:1" (which aren't
> really an interface, but are a deprecated method of adding multiple IP
> addresses to a single interface). Since only the base interface
> ("eth0") is really a device, only it has an entry in /sys/class/net.
> if (!state) {
>    /* missing operstate is *not* an error. It could be due to an
>     * alias interface, which has not entry in /sys/class/net at

s/not/no/

ACK with that tweak.

[Laine Stump]

On 01/27/2015 12:56 PM, Eric Blake wrote:
> On 01/27/2015 10:48 AM, Laine Stump wrote:
> > This can happen for alias "interfaces", e.g: "eth0:1" (which aren't
> > really an interface, but are a deprecated method of adding multiple IP
> > addresses to a single interface). Since only the base interface
> > ("eth0") is really a device, only it has an entry in /sys/class/net.
> > if (!state) {
> >    /* missing operstate is *not* an error. It could be due to an
> >     * alias interface, which has not entry in /sys/class/net at
>
> s/not/no/
>
> ACK with that tweak.

Thanks for the quick response! I've pushed this patch (as well as the
one from yesterday).