libxl: pass env vars to libxl__exec

Add another parameter to libxl__exec call that contains the
environment variables to use when performing the execvp call.

Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl.c

@@ -1307,7 +1307,7 @@ int libxl_vncviewer_exec(libxl_ctx *ctx, uint32_t domid, int autopass)
         args[2] = "-autopass";
     }
 
-    libxl__exec(autopass_fd, -1, -1, args[0], args);
+    libxl__exec(gc, autopass_fd, -1, -1, args[0], args, NULL);
     abort();
 
  x_fail:

tools/libxl/libxl_bootloader.c

@@ -385,6 +385,7 @@ static void bootloader_gotptys(libxl__egc *egc, libxl__openpty_state *op)
     libxl__bootloader_state *bl = CONTAINER_OF(op, *bl, openpty);
     STATE_AO_GC(bl->ao);
     int rc, r;
+    char *const env[] = { "TERM", "vt100", NULL };
 
     if (bl->openpty.rc) {
         rc = bl->openpty.rc;
@@ -478,8 +479,7 @@ static void bootloader_gotptys(libxl__egc *egc, libxl__openpty_state *op)
         /* child */
         r = login_tty(libxl__carefd_fd(bl->ptys[0].slave));
         if (r) { LOGE(ERROR, "login_tty failed"); exit(-1); }
-        setenv("TERM", "vt100", 1);
-        libxl__exec(-1, -1, -1, bl->args[0], (char**)bl->args);
+        libxl__exec(gc, -1, -1, -1, bl->args[0], (char **) bl->args, env);
         exit(-1);
     }
 

tools/libxl/libxl_dm.c

@@ -1016,7 +1016,7 @@ retry_transaction:
         goto out_close;
     if (!rc) { /* inner child */
         setsid();
-        libxl__exec(null, logfile_w, logfile_w, dm, args);
+        libxl__exec(gc, null, logfile_w, logfile_w, dm, args, NULL);
     }
 
     rc = 0;

tools/libxl/libxl_exec.c

@@ -66,8 +66,8 @@ static void check_open_fds(const char *what)
     if (badness) abort();
 }
 
-void libxl__exec(int stdinfd, int stdoutfd, int stderrfd, const char *arg0,
-                char **args)
+void libxl__exec(libxl__gc *gc, int stdinfd, int stdoutfd, int stderrfd,
+                 const char *arg0, char *const args[], char *const env[])
      /* call this in the child */
 {
     if (stdinfd != -1)
@@ -90,8 +90,18 @@ void libxl__exec(int stdinfd, int stdoutfd, int stderrfd, const char *arg0,
     /* in case our caller set it to IGN.  subprocesses are entitled
      * to assume they got DFL. */
 
+    if (env != NULL) {
+        for (int i = 0; env[i] != NULL && env[i+1] != NULL; i += 2) {
+            if (setenv(env[i], env[i+1], 1) < 0) {
+                LOGEV(ERROR, errno, "setting env vars (%s = %s)",
+                                    env[i], env[i+1]);
+                goto out;
+            }
+        }
+    }
     execvp(arg0, args);
 
+out:
     fprintf(stderr, "libxl: cannot execute %s: %s\n", arg0, strerror(errno));
     _exit(-1);
 }

tools/libxl/libxl_internal.h

@@ -1141,8 +1141,24 @@ _hidden int libxl__wait_for_offspring(libxl__gc *gc,
 
  /* low-level stuff, for synchronous subprocesses etc. */
 
-_hidden void libxl__exec(int stdinfd, int stdoutfd, int stderrfd,
-               const char *arg0, char **args); // logs errors, never returns
+/*
+ * env should be passed using the following format,
+ *
+ * env[0]: name of env variable
+ * env[1]: value of env variable
+ * env[n]: ...
+ *
+ * So it efectively becomes something like:
+ * export env[n]=env[n+1]
+ * (where n%2 = 0)
+ *
+ * The last entry of the array always has to be NULL.
+ *
+ * Logs errors, never returns.
+ */
+_hidden  void libxl__exec(libxl__gc *gc, int stdinfd, int stdoutfd,
+                          int stderrfd, const char *arg0, char *const args[],
+                          char *const env[]);
 
 /* from xl_create */