Re: [PATCH 14/23] libmultipath: add libmp_dm_exit()

[Benjamin Marzinski <bmarzins@redhat.com>]

On Thu, Sep 24, 2020 at 03:40:45PM +0200, mwilck@suse.com wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> This function prepares for calling dm_lib_exit() on program exit.
> It undoes changes to libdm internals done by libmultipath.
> It doesn't call dm_lib_exit(), as the caller may want to keep
> libdm active.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  libmultipath/config.c    |  1 +
>  libmultipath/config.h    |  2 ++
>  libmultipath/devmapper.c | 10 ++++++++++
>  libmultipath/devmapper.h |  1 +
>  4 files changed, 14 insertions(+)
> 
> diff --git a/libmultipath/config.c b/libmultipath/config.c
> index fbb66b3..8097838 100644
> --- a/libmultipath/config.c
> +++ b/libmultipath/config.c
> @@ -65,6 +65,7 @@ int libmultipath_init(void)
>  static void _libmultipath_exit(void)
>  {
>  	libmultipath_exit_called = true;
> +	libmp_dm_exit();
>  	udev_unref(udev);
>  }

What if the caller wanted to control the dm initialization themselves,
and used skip_libmp_dm_init()? We need to track that and not undo
their changes.

-Ben

>  
> diff --git a/libmultipath/config.h b/libmultipath/config.h
> index dac4e8f..fc614f0 100644
> --- a/libmultipath/config.h
> +++ b/libmultipath/config.h
> @@ -270,6 +270,8 @@ int libmultipath_init(void);
>   *
>   * This function un-initializes libmultipath data structures.
>   * It is recommended to call this function at program exit.
> + * If the application also calls dm_lib_exit(), it should do so
> + * after libmultipath_exit().
>   *
>   * Calls to libmultipath_init() after libmultipath_exit() will fail
>   * (in other words, libmultipath can't be re-initialized).
> diff --git a/libmultipath/devmapper.c b/libmultipath/devmapper.c
> index 2e3ae8a..5a2e1e7 100644
> --- a/libmultipath/devmapper.c
> +++ b/libmultipath/devmapper.c
> @@ -333,6 +333,16 @@ void libmp_udev_set_sync_support(int on)
>  	libmp_dm_udev_sync = !!on;
>  }
>  
> +void libmp_dm_exit(void)
> +{
> +	/* switch back to default libdm logging */
> +	dm_log_init(NULL);
> +#ifdef LIBDM_API_HOLD_CONTROL
> +	/* make sure control fd is closed in dm_lib_release() */
> +	dm_hold_control_dev(0);
> +#endif
> +}
> +
>  static void libmp_dm_init(void)
>  {
>  	struct config *conf;
> diff --git a/libmultipath/devmapper.h b/libmultipath/devmapper.h
> index 158057e..ecf2e66 100644
> --- a/libmultipath/devmapper.h
> +++ b/libmultipath/devmapper.h
> @@ -35,6 +35,7 @@ enum {
>  
>  int dm_prereq(unsigned int *v);
>  void skip_libmp_dm_init(void);
> +void libmp_dm_exit(void);
>  void libmp_udev_set_sync_support(int on);
>  struct dm_task *libmp_dm_task_create(int task);
>  int dm_simplecmd_flush (int, const char *, uint16_t);
> -- 
> 2.28.0