Re: [PATCH] modules: load modules from versioned /var/run dir

[Stefan Hajnoczi]

On Fri, Mar 06, 2020 at 02:26:48PM +0100, Christian Ehrhardt wrote:
> On upgrades the old .so files usually are replaced. But on the other
> hand since a qemu process represents a guest instance it is usually kept
> around.
> 
> That makes late addition of dynamic features e.g. 'hot-attach of a ceph
> disk' fail by trying to load a new version of e.f. block-rbd.so into an
> old still running qemu binary.
> 
> This adds a fallback to also load modules from a versioned directory in the
> temporary /var/run path. That way qemu is providing a way for packaging
> to store modules of an upgraded qemu package as needed until the next reboot.
> 
> An example how that can then be used in packaging can be seen in:
> https://git.launchpad.net/~paelzer/ubuntu/+source/qemu/log/?h=bug-1847361-miss-old-so-on-upgrade-UBUNTU
> 
> Fixes: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1847361
> Signed-off-by: Christian Ehrhardt <address@hidden>
> ---
>  util/module.c | 7 +++++++
>  1 file changed, 7 insertions(+)

CCing Debian, Fedora, and Red Hat package maintainers in case they have
comments.

The use of /var/run makes me a little uneasy.  I guess it's related to
wanting to uninstall the old package so the .so in their original
location cannot be used (even if they had a versioned path)?

I'm not a package maintainer though so I hope the others will make
suggestions if there are other solutions :).

> 
> diff --git a/util/module.c b/util/module.c
> index 236a7bb52a..d2446104be 100644
> --- a/util/module.c
> +++ b/util/module.c
> @@ -19,6 +19,7 @@
>  #endif
>  #include "qemu/queue.h"
>  #include "qemu/module.h"
> +#include "qemu-version.h"
>  
>  typedef struct ModuleEntry
>  {
> @@ -170,6 +171,7 @@ bool module_load_one(const char *prefix, const char 
> *lib_name)
>  #ifdef CONFIG_MODULES
>      char *fname = NULL;
>      char *exec_dir;
> +    char *version_dir;
>      const char *search_dir;
>      char *dirs[4];
>      char *module_name;
> @@ -201,6 +203,11 @@ bool module_load_one(const char *prefix, const char 
> *lib_name)
>      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 ? : "");
> +    version_dir = g_strcanon(g_strdup(QEMU_PKGVERSION),
> +                             G_CSET_A_2_Z G_CSET_a_2_z G_CSET_DIGITS "+-.~",
> +                             '_');
> +    dirs[n_dirs++] = g_strdup_printf("/var/run/qemu/%s", version_dir);
> +
>      assert(n_dirs <= ARRAY_SIZE(dirs));
>  
>      g_free(exec_dir);
> -- 
> 2.25.1
> 
>

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