[Qemu-devel] [PATCH] module: Use QEMU_MODULE_PATH as a search path

[ryang <decatf@gmail.com>]

The current paths for modules are CONFIG_QEMU_MODDIR and paths relative
to the executable. Qemu and its modules can be installed and executed in
paths that are different from these search paths. This change allows
a search path to be specified by environment variable.

An example usage for this is postmarketOS[1]. This is a build environment
for Alpine Linux. It sets up Alpine Linux in a chroot environment.
Alpine's Qemu packages are installed in the chroot. The Alpine Linux Qemu
package is used to test compiled Alpine Linux system images. This way there
isn't a reliance on the which ever version of Qemu the host system / distro
provides.

postmarketOS executes Qemu on host system outside of the chroot
The Qemu module search path needs to point to the location of the
chroot relative to the host system.

e.g.
The root of the Alpine Linux chroot is:
~/.local/var/pmbootstrap/chroot_native/

Alpine's Qemu is installed at
~/.local/var/pmbootstrap/chroot_native/usr/bin/

The Qemu module search path needs to be:
QEMU_MODULE_PATH=~/.local/var/pmbootstrap/chroot_native/usr/lib/qemu/

[1] https://postmarketos.org/

Signed-off-by: ryang <decatf@gmail.com>
---

Apologies if this is not sent to the correct maintainers. I couldn't
find anyone listed for this specific file in MAINTAINERS or by
using get_maintainer.pl. I'm sending this to the orignal author
and maintainers involved with the patch that added module loading.

 util/module.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/util/module.c b/util/module.c
index c909737..f9088a5 100644
--- a/util/module.c
+++ b/util/module.c
@@ -162,9 +162,10 @@ void module_load_one(const char *prefix, const char *lib_name)
 #ifdef CONFIG_MODULES
     char *fname = NULL;
     char *exec_dir;
-    char *dirs[3];
+    char *search_path;
+    char *dirs[4];
     char *module_name;
-    int i = 0;
+    int i = 0, n_dirs;
     int ret;
     static GHashTable *loaded_modules;
 
@@ -186,14 +187,18 @@ void module_load_one(const char *prefix, const char *lib_name)
     g_hash_table_insert(loaded_modules, module_name, module_name);
 
     exec_dir = qemu_get_exec_dir();
-    dirs[i++] = g_strdup_printf("%s", CONFIG_QEMU_MODDIR);
-    dirs[i++] = g_strdup_printf("%s/..", exec_dir ? : "");
-    dirs[i++] = g_strdup_printf("%s", exec_dir ? : "");
-    assert(i == ARRAY_SIZE(dirs));
+    search_path = getenv("QEMU_MODULE_PATH");
+    if (search_path != NULL)
+        dirs[n_dirs++] = g_strdup_printf("%s", search_path);
+    dirs[n_dirs++] = g_strdup_printf("%s", CONFIG_QEMU_MODDIR);
+    dirs[n_dirs++] = g_strdup_printf("%s/..", exec_dir ? : "");
+    dirs[n_dirs++] = g_strdup_printf("%s", exec_dir ? : "");
+    assert(n_dirs <= ARRAY_SIZE(dirs));
+
     g_free(exec_dir);
     exec_dir = NULL;
 
-    for (i = 0; i < ARRAY_SIZE(dirs); i++) {
+    for (i = 0; i < n_dirs; i++) {
         fname = g_strdup_printf("%s/%s%s",
                 dirs[i], module_name, HOST_DSOSUF);
         ret = module_load_file(fname);
@@ -205,7 +210,7 @@ void module_load_one(const char *prefix, const char *lib_name)
         }
     }
 
-    for (i = 0; i < ARRAY_SIZE(dirs); i++) {
+    for (i = 0; i < n_dirs; i++) {
         g_free(dirs[i]);
     }
 
-- 
2.7.4