[RFC v2 6/6] linux-user: Add '-native-bypass' option

[Yeqi Fu]

Signed-off-by: Yeqi Fu <fufuyqqqqqq@gmail.com>
---
 include/qemu/envlist.h |  1 +
 linux-user/main.c      | 23 +++++++++++++++++
 util/envlist.c         | 56 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+)

diff --git a/include/qemu/envlist.h b/include/qemu/envlist.h
index 6006dfae44..865eb18e17 100644
--- a/include/qemu/envlist.h
+++ b/include/qemu/envlist.h
@@ -7,6 +7,7 @@ envlist_t *envlist_create(void);
 void envlist_free(envlist_t *);
 int envlist_setenv(envlist_t *, const char *);
 int envlist_unsetenv(envlist_t *, const char *);
+int envlist_appendenv(envlist_t *, const char *, const char *);
 int envlist_parse_set(envlist_t *, const char *);
 int envlist_parse_unset(envlist_t *, const char *);
 char **envlist_to_environ(const envlist_t *, size_t *);
diff --git a/linux-user/main.c b/linux-user/main.c
index 5e6b2e1714..313c116b3b 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -125,6 +125,8 @@ static void usage(int exitcode);
 static const char *interp_prefix = CONFIG_QEMU_INTERP_PREFIX;
 const char *qemu_uname_release;
 
+static const char *native_lib;
+
 #if !defined(TARGET_DEFAULT_STACK_SIZE)
 /* XXX: on x86 MAP_GROWSDOWN only works if ESP <= address + 32, so
    we allocate a bigger stack. Need a better solution, for example
@@ -293,6 +295,13 @@ static void handle_arg_set_env(const char *arg)
     free(r);
 }
 
+#if defined(CONFIG_USER_ONLY)  && defined(CONFIG_USER_NATIVE_CALL)
+static void handle_arg_native_bypass(const char *arg)
+{
+    native_lib = arg;
+}
+#endif
+
 static void handle_arg_unset_env(const char *arg)
 {
     char *r, *p, *token;
@@ -522,6 +531,10 @@ static const struct qemu_argument arg_table[] = {
      "",           "Generate a /tmp/perf-${pid}.map file for perf"},
     {"jitdump",    "QEMU_JITDUMP",     false, handle_arg_jitdump,
      "",           "Generate a jit-${pid}.dump file for perf"},
+#if defined(CONFIG_USER_ONLY)  && defined(CONFIG_USER_NATIVE_CALL)
+    {"native-bypass", "QEMU_NATIVE_BYPASS", true, handle_arg_native_bypass,
+     "",           "native bypass for library calls in user mode only."},
+#endif
     {NULL, NULL, false, NULL, NULL, NULL}
 };
 
@@ -826,6 +839,16 @@ int main(int argc, char **argv, char **envp)
         }
     }
 
+    /* Set the library for native bypass  */
+    if (native_lib != NULL) {
+        char *token = malloc(strlen(native_lib) + 12);
+        strcpy(token, "LD_PRELOAD=");
+        strcat(token, native_lib);
+         if (envlist_appendenv(envlist, token, ":") != 0) {
+            usage(EXIT_FAILURE);
+        }
+    }
+
     target_environ = envlist_to_environ(envlist, NULL);
     envlist_free(envlist);
 
diff --git a/util/envlist.c b/util/envlist.c
index db937c0427..713d52497e 100644
--- a/util/envlist.c
+++ b/util/envlist.c
@@ -201,6 +201,62 @@ envlist_unsetenv(envlist_t *envlist, const char *env)
     return (0);
 }
 
+/*
+ * Appends environment value to envlist. If the environment
+ * variable already exists, the new value is appended to the
+ * existing one.
+ *
+ * Returns 0 in success, errno otherwise.
+ */
+int
+envlist_appendenv(envlist_t *envlist, const char *env, const char *separator)
+{
+    struct envlist_entry *entry = NULL;
+    const char *eq_sign;
+    size_t envname_len;
+
+    if ((envlist == NULL) || (env == NULL)) {
+        return (EINVAL);
+    }
+
+    /* find out first equals sign in given env */
+    eq_sign = strchr(env, '=');
+    if (eq_sign == NULL) {
+        return (EINVAL);
+    }
+    envname_len = eq_sign - env + 1;
+
+    /*
+     * If there already exists variable with given name,
+     * we append the new value to the existing one.
+     */
+    for (entry = envlist->el_entries.lh_first; entry != NULL;
+        entry = entry->ev_link.le_next) {
+        if (strncmp(entry->ev_var, env, envname_len) == 0) {
+            break;
+        }
+    }
+
+    if (entry != NULL) {
+        char *new_env_value = NULL;
+        size_t new_env_len = strlen(entry->ev_var) + strlen(eq_sign)
+            + strlen(separator) + 1;
+        new_env_value = g_malloc(new_env_len);
+        strcpy(new_env_value, entry->ev_var);
+        strcat(new_env_value, separator);
+        strcat(new_env_value, eq_sign + 1);
+        g_free((char *)entry->ev_var);
+        entry->ev_var = new_env_value;
+    } else {
+        envlist->el_count++;
+        entry = g_malloc(sizeof(*entry));
+        entry->ev_var = g_strdup(env);
+        QLIST_INSERT_HEAD(&envlist->el_entries, entry, ev_link);
+    }
+
+    return (0);
+}
+
 /*
  * Returns given envlist as array of strings (in same form that
  * global variable environ is).  Caller must free returned memory
-- 
2.34.1