[Qemu-devel] [PATCH v3] module: Use QEMU_MODULE_PATH as a search path

[Qemu-devel] [PATCH v3] module: Use QEMU_MODULE_PATH as a search path

[ryang]

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>
---

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

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

diff --git a/util/module.c b/util/module.c
index c909737..612f00e 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 = 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);
 
     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 +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]);
     }
 
-- 
2.7.4

Re: [Qemu-devel] [PATCH v3] module: Use QEMU_MODULE_PATH as a search path

[Daniel P. Berrangé]

On Tue, Jul 03, 2018 at 03:19:04PM -0400, ryang wrote:
> 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>
> ---
> 
> v2:
>  - fix checkpatch errors
> v3:
>  - initialize n_dirs variable
> 
>  util/module.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/util/module.c b/util/module.c
> index c909737..612f00e 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;

This should be "const"

> +    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);
>  
>      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);
> +    }

For an env variable named with a "_PATH", I'd expect to have a colon
separated list of directories, but this only allows a single directory.

If we only want a single dir for simplicity, then use a _DIR suffix
instead of _PATH, otherwise implement support for splitting on ":"

> +    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]);
>      }
>  
> -- 
> 2.7.4
> 
> 

Regards,
Daniel
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