gnu: ucx: Avoid relying on /sys/class/net.

This fixes test failures of packages that use Open MPI, whereby UCX
would error out due to /sys/class/net being unavailable in the build
chroot that the daemon sets up.

* gnu/packages/patches/ucx-tcp-iface-ioctl.patch: New file.
* gnu/packages/fabric-management.scm (ucx)[source]: Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/local.mk

@@ -1392,6 +1392,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/tuxpaint-stamps-path.patch		\
   %D%/packages/patches/txr-shell.patch				\
   %D%/packages/patches/u-boot-fix-mkimage-header-verification.patch	\
+  %D%/packages/patches/ucx-tcp-iface-ioctl.patch		\
   %D%/packages/patches/udiskie-no-appindicator.patch		\
   %D%/packages/patches/unzip-CVE-2014-8139.patch		\
   %D%/packages/patches/unzip-CVE-2014-8140.patch		\

gnu/packages/fabric-management.scm

@@ -190,7 +190,8 @@ (define-public ucx
               (file-name (git-file-name name version))
               (sha256
                (base32
-                "0x3clvy716i7va4m4adgx6ihjsfnzrkdizhxz5v52944dkglpc8n"))))
+                "0x3clvy716i7va4m4adgx6ihjsfnzrkdizhxz5v52944dkglpc8n"))
+              (patches (search-patches "ucx-tcp-iface-ioctl.patch"))))
     (build-system gnu-build-system)
     (arguments
      '( ;; These are some of the flags found in 'contrib/configure-release'.

gnu/packages/patches/ucx-tcp-iface-ioctl.patch

@@ -0,0 +1,109 @@
+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 81ad459..10024a6 100644
+--- a/src/uct/tcp/tcp_iface.c
++++ b/src/uct/tcp/tcp_iface.c
+@@ -12,6 +12,8 @@
+ #include <sys/poll.h>
+ #include <netinet/tcp.h>
+ #include <dirent.h>
++#include <net/if.h>
++#include <sys/ioctl.h>
+ 
+ static ucs_config_field_t uct_tcp_iface_config_table[] = {
+   {"", "MAX_SHORT=8k", NULL,
+@@ -483,6 +485,70 @@ 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_resource_desc_t **resource_p,
++					unsigned *num_resources_p)
++{
++    int sock, err, i;
++    uct_tl_resource_desc_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)) {
++            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].tl_name, sizeof(resources[i].tl_name),
++                          "%s", UCT_TCP_NAME);
++        ucs_snprintf_zero(resources[i].dev_name, sizeof(resources[i].dev_name),
++                          "%s", name);
++        resources[i].dev_type = UCT_DEVICE_TYPE_NET;
++        ++num_resources;
++    }
++
++    *num_resources_p = num_resources;
++    *resource_p      = resources;
++    status           = UCS_OK;
++
++out:
++    if (sock >= 0) close(sock);
++    return status;
++}
++
+ static ucs_status_t uct_tcp_query_tl_resources(uct_md_h md,
+                                                uct_tl_resource_desc_t **resource_p,
+                                                unsigned *num_resources_p)
+@@ -496,9 +562,9 @@ static ucs_status_t uct_tcp_query_tl_resources(uct_md_h md,
+ 
+     dir = opendir(netdev_dir);
+     if (dir == NULL) {
+-        ucs_error("opendir(%s) failed: %m", 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, resource_p, num_resources_p);
+     }
+ 
+     resources     = NULL;
+@@ -543,6 +609,5 @@ static ucs_status_t uct_tcp_query_tl_resources(uct_md_h md,
+ 
+ out_closedir:
+     closedir(dir);
+-out:
+     return status;
+ }