Simplify read_random_bytes.

kernel.c

@@ -84,21 +84,24 @@ gettime(struct timeval *tv)
 /* If /dev/urandom doesn't exist, this will fail with ENOENT, which the
    caller will deal with gracefully. */
 
-int
+ssize_t
 read_random_bytes(void *buf, size_t len)
 {
     int fd;
-    int rc;
+    size_t rc;
 
     fd = open("/dev/urandom", O_RDONLY);
     if(fd < 0) {
-        rc = -1;
-    } else {
-        rc = read(fd, buf, len);
-        if(rc < 0 || (unsigned)rc < len)
-            rc = -1;
-        close(fd);
+        errno = ENOSYS;
+        return -1;
     }
+
+    rc = read(fd, buf, len);
+    if(rc < len)
+        rc = -1;
+
+    close(fd);
+
     return rc;
 }
 

kernel.h

@@ -77,6 +77,6 @@ int kernel_addresses(char *ifname, int ifindex, int ll,
                      struct kernel_route *routes, int maxroutes);
 int if_eui64(char *ifname, int ifindex, unsigned char *eui);
 int gettime(struct timeval *tv);
-int read_random_bytes(void *buf, size_t len);
+ssize_t read_random_bytes(void *buf, size_t len);
 int kernel_older_than(const char *sysname, int version, int sub_version);
 int kernel_has_ipv6_subtrees(void);