Populate /dev/std{in,out,err} symlinks in LXC containers

Some applications expect /dev/std{in,out,err} to exist. Populate
them during container startup as symlinks to /proc/self/fd

src/lxc/lxc_container.c

@@ -584,6 +584,15 @@ static int lxcContainerPopulateDevices(char **ttyPaths, size_t nttyPaths)
         { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_RANDOM, 0666, "/dev/random" },
         { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_URANDOM, 0666, "/dev/urandom" },
     };
+    const struct {
+        const char *src;
+        const char *dst;
+    } links[] = {
+        { "/proc/self/fd/0", "/dev/stdin" },
+        { "/proc/self/fd/1", "/dev/stdout" },
+        { "/proc/self/fd/2", "/dev/stderr" },
+        { "/proc/self/fd", "/dev/fd" },
+    };
 
     /* Populate /dev/ with a few important bits */
     for (i = 0 ; i < ARRAY_CARDINALITY(devs) ; i++) {
@@ -597,6 +606,15 @@ static int lxcContainerPopulateDevices(char **ttyPaths, size_t nttyPaths)
         }
     }
 
+    for (i = 0 ; i < ARRAY_CARDINALITY(links) ; i++) {
+        if (symlink(links[i].src, links[i].dst) < 0) {
+            virReportSystemError(errno,
+                                 _("Failed to symlink device %s to %s"),
+                                 links[i].dst, links[i].src);
+            return -1;
+        }
+    }
+
     if (access("/dev/pts/ptmx", W_OK) == 0) {
         /* We have private devpts capability, so bind that */
         if (virFileTouch("/dev/ptmx", 0666) < 0)