Since /sys is unavailable in build environments, the list of available
TCP network interfaces cannot be obtained via /sys/class/net.  This patch
provides alternative code that uses the SIOCGIFCONF ioctl to get the
names of the available TCP network interfaces.

diff --git a/src/uct/tcp/tcp_iface.c b/src/uct/tcp/tcp_iface.c
index cad4a2709..7c1d2c9de 100644
--- a/src/uct/tcp/tcp_iface.c
+++ b/src/uct/tcp/tcp_iface.c
@@ -17,6 +17,8 @@
 #include <sys/poll.h>
 #include <netinet/tcp.h>
 #include <dirent.h>
+#include <net/if.h>
+#include <sys/ioctl.h>
 
 
 extern ucs_class_t UCS_CLASS_DECL_NAME(uct_tcp_iface_t);
@@ -586,6 +588,68 @@ static UCS_CLASS_DEFINE_NEW_FUNC(uct_tcp_iface_t, uct_iface_t, uct_md_h,
                                  uct_worker_h, const uct_iface_params_t*,
                                  const uct_iface_config_t*);
 
+/* Fetch information about available network devices through an ioctl.  */
+static ucs_status_t query_devices_ioctl(uct_md_h md,
+					uct_tl_device_resource_t **tl_devices_p,
+					unsigned *num_tl_devices_p)
+{
+    int sock, err, i;
+    uct_tl_device_resource_t *resources, *tmp;
+    unsigned num_resources;
+    ucs_status_t status;
+    struct ifconf conf;
+    struct ifreq reqs[10];
+
+    conf.ifc_len = sizeof reqs;
+    conf.ifc_req = reqs;
+
+    sock = socket(SOCK_STREAM, AF_INET, 0);
+    if (sock < 0) {
+	ucs_error("socket(2) failed: %m");
+	status = UCS_ERR_IO_ERROR;
+	goto out;
+    }
+
+    err = ioctl(sock, SIOCGIFCONF, &conf);
+    if (err < 0) {
+	ucs_error("SIOCGIFCONF ioctl failed: %m");
+	status = UCS_ERR_IO_ERROR;
+	goto out;
+    }
+
+    resources     = NULL;
+    num_resources = 0;
+    for (i = 0; i < conf.ifc_len / sizeof(struct ifreq); i++) {
+	const char *name = reqs[i].ifr_name;
+
+        if (!ucs_netif_is_active(name, AF_INET)) {
+            continue;
+        }
+
+        tmp = ucs_realloc(resources, sizeof(*resources) * (num_resources + 1),
+                          "tcp resources");
+        if (tmp == NULL) {
+            ucs_free(resources);
+            status = UCS_ERR_NO_MEMORY;
+            goto out;
+        }
+        resources = tmp;
+
+        ucs_snprintf_zero(resources[i].name, sizeof(resources[i].name),
+                          "%s", name);
+        resources[i].type = UCT_DEVICE_TYPE_NET;
+        ++num_resources;
+    }
+
+    *num_tl_devices_p = num_resources;
+    *tl_devices_p     = resources;
+    status            = UCS_OK;
+
+out:
+    if (sock >= 0) close(sock);
+    return status;
+}
+
 ucs_status_t uct_tcp_query_devices(uct_md_h md,
                                    uct_tl_device_resource_t **devices_p,
                                    unsigned *num_devices_p)
@@ -599,9 +663,9 @@ ucs_status_t uct_tcp_query_devices(uct_md_h md,
 
     dir = opendir(UCT_TCP_IFACE_NETDEV_DIR);
     if (dir == NULL) {
-        ucs_error("opendir(%s) failed: %m", UCT_TCP_IFACE_NETDEV_DIR);
-        status = UCS_ERR_IO_ERROR;
-        goto out;
+	/* When /sys is unavailable, as can be the case in a container,
+	 * resort to a good old 'ioctl'.  */
+	return query_devices_ioctl(md, devices_p, num_devices_p);
     }
 
     devices     = NULL;
@@ -655,7 +719,6 @@ ucs_status_t uct_tcp_query_devices(uct_md_h md,
 
 out_closedir:
     closedir(dir);
-out:
     return status;
 }
 
...<span class='msg-tooltip'>* gnu/packages/plotutils.scm (guile-charting): Update to commit 75f755b.
[source]: Remove 'snippet' and 'modules'.  Switch to 'git-fetch'.
[native-inputs]: Add AUTOCONF, AUTOMAKE, and TEXINFO.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-24 23:22:45 +0100'>2020-11-24</span></td><td><a href='/guix/commit/gnu/packages/plotutils.scm?id=66283b8fcb2e46cdb479f73bd595c137db9221b2'>gnu: asymptote: Update to 2.68.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/plotutils.scm (asymptote): Update to 2.68.
</span></span></td><td>Nicolas Goaziou</td></tr>