module: Use QEMU_MODULE_PATH as a search path

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 <[email protected]>

---

v2:
- fix checkpatch errors
v3:
- initialize n_dirs variable

 util/module.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

util/module.c +0 -0

index c909737..612f00e 100644

util/module.c +2 -1

+    char *dirs[4];
     char *module_name;
-    int i = 0;
+    int i = 0, n_dirs = 0;
     int ret;
     static GHashTable *loaded_modules;
 

@@ -186,14 +187,19 @@ void module_load_one(const char *prefix, const char *lib_name)
     g_hash_table_insert(loaded_modules, module_name, module_name);

util/module.c +7 -2

+    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 +211,7 @@ 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]);
     }
 

Signature · 1 line

2.7.4