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[Qemu-devel] Environment variables for user-mode QEMU

From: Thomas Schwinge
Subject: [Qemu-devel] Environment variables for user-mode QEMU
Date: Wed, 24 Apr 2013 15:16:27 +0200
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We have a need to pass environment variable assignments containing commas
to user-mode QEMU.  The usage information currently says:

    You can use -E and -U options or the QEMU_SET_ENV and
    QEMU_UNSET_ENV environment variables to set and unset
    environment variables for the target process.
    It is possible to provide several variables by separating them
    by commas in getsubopt(3) style. Additionally it is possible to
    provide the -E and -U options multiple times.

    $ env -i x86_64-linux-user/qemu-x86_64 -E x=y,y=z /usr/bin/printenv

Instead of this, we'd like to see:

    $ env -i x86_64-linux-user/qemu-x86_64 -E x=y,y=z /usr/bin/printenv

Due to the tokenization based on comma in
linux-user/main.c:handle_arg_set_env, there is currently no way to
achieve this -- other than pre-setting environment variables before
running user-mode QEMU, which obviously isn't always desirable/possible

Assuming there is a consensus, how would you like this implemented?

Is it OK to change the semantics of -E (as well as -U, for symmetry?) to
not handle multiple environment variable assignments (preliminary patch
below), or does that functionality need to be preserved?  Something needs
to be done about QEMU_SET_ENV and QEMU_UNSET_ENV then (if anyone is using
these at all, which we can't disprove), as these are not very useful if
they can handle only one environment variable.

Or, should we perhaps have a new -env option that causes any later
non-option arguments, that contain an equal sign, to be handled as
environment variable assignments, just like the env command does?

    $ env -i x86_64-linux-user/qemu-x86_64 [some options] -env [more options] 
a=b,c d=e,f=a /usr/bin/printenv

I think I might prefer that solution.  As it is a new option, it also
won't interfere with anyone's usage/expectations of the current behavior.
Anyway, here is the incomplete patch, changing the behavior of -E and -U
(as well as the corresponding QEMU_SET_ENV and QEMU_UNSET_ENV):

diff --git linux-user/main.c linux-user/main.c
index 4e92a0b..62ff963 100644
--- linux-user/main.c
+++ linux-user/main.c
@@ -3204,26 +3204,16 @@ static void handle_arg_log_filename(const char *arg)
 static void handle_arg_set_env(const char *arg)
-    char *r, *p, *token;
-    r = p = strdup(arg);
-    while ((token = strsep(&p, ",")) != NULL) {
-        if (envlist_setenv(envlist, token) != 0) {
-            usage();
-        }
+    if (envlist_setenv(envlist, arg) != 0) {
+        usage();
-    free(r);
 static void handle_arg_unset_env(const char *arg)
-    char *r, *p, *token;
-    r = p = strdup(arg);
-    while ((token = strsep(&p, ",")) != NULL) {
-        if (envlist_unsetenv(envlist, token) != 0) {
-            usage();
-        }
+    if (envlist_unsetenv(envlist, arg) != 0) {
+        usage();
-    free(r);
 static void handle_arg_argv0(const char *arg)


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