On Fri, Oct 16, 2020 at 12:43:25PM +0200, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> With these symbols added, applications using libmultipath don't
> need to define global variables "udev" and "logsink" any more.
> This comes at the cost of having to call an init function.
> Currently, libmultipath_init() does nothing but initialize
> "udev".
>
> The linker's symbol lookup order still allows applications to use
> their own "logsink" and "udev" variables, which will take precendence
> over libmultipath's internal ones. In this case, calling
> libmultipath_init() can be skipped, but like before,
> udev should be initialized (using udev_new()) before making any
> libmultipath calls.
>
Reviewed-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> libmultipath/config.c | 41 +++++++++++++++++++++++++++
> libmultipath/config.h | 46 ++++++++++++++++++++++++++++++-
> libmultipath/debug.c | 2 ++
> libmultipath/libmultipath.version | 8 ++++++
> 4 files changed, 96 insertions(+), 1 deletion(-)
>
> diff --git a/libmultipath/config.c b/libmultipath/config.c
> index 01b77df..f74417c 100644
> --- a/libmultipath/config.c
> +++ b/libmultipath/config.c
> @@ -27,6 +27,47 @@
> #include "mpath_cmd.h"
> #include "propsel.h"
>
> +/*
> + * We don't support re-initialization after
> + * libmultipath_exit().
> + */
> +static bool libmultipath_exit_called;
> +static pthread_once_t _init_once = PTHREAD_ONCE_INIT;
> +static pthread_once_t _exit_once = PTHREAD_ONCE_INIT;
> +struct udev *udev;
> +
> +static void _udev_init(void)
> +{
> + if (udev)
> + udev_ref(udev);
> + else
> + udev = udev_new();
> + if (!udev)
> + condlog(0, "%s: failed to initialize udev", __func__);
> +}
> +
> +static bool _is_libmultipath_initialized(void)
> +{
> + return !libmultipath_exit_called && !!udev;
> +}
> +
> +int libmultipath_init(void)
> +{
> + pthread_once(&_init_once, _udev_init);
> + return !_is_libmultipath_initialized();
> +}
> +
> +static void _libmultipath_exit(void)
> +{
> + libmultipath_exit_called = true;
> + udev_unref(udev);
> +}
> +
> +void libmultipath_exit(void)
> +{
> + pthread_once(&_exit_once, _libmultipath_exit);
> +}
> +
> static struct config __internal_config;
> struct config *libmp_get_multipath_config(void)
> {
> diff --git a/libmultipath/config.h b/libmultipath/config.h
> index 0329de2..f478df7 100644
> --- a/libmultipath/config.h
> +++ b/libmultipath/config.h
> @@ -233,7 +233,51 @@ struct config {
> char *enable_foreign;
> };
>
> -extern struct udev * udev;
> +/**
> + * extern variable: udev
> + *
> + * A &struct udev instance used by libmultipath. libmultipath expects
> + * a valid, initialized &struct udev in this variable.
> + * An application can define this variable itself, in which case
> + * the applications's instance will take precedence.
> + * The application can initialize and destroy this variable by
> + * calling libmultipath_init() and libmultipath_exit(), respectively,
> + * whether or not it defines the variable itself.
> + * An application can initialize udev with udev_new() before calling
> + * libmultipath_init(), e.g. if it has to make libudev calls before
> + * libmultipath calls. If an application wants to keep using the
> + * udev variable after calling libmultipath_exit(), it should have taken
> + * an additional reference on it beforehand. This is the case e.g.
> + * after initiazing udev with udev_new().
> + */
> +extern struct udev *udev;
> +
> +/**
> + * libmultipath_init() - library initialization
> + *
> + * This function initializes libmultipath data structures.
> + * It is light-weight; some other initializations, like device-mapper
> + * initialization, are done lazily when the respective functionality
> + * is required.
> + *
> + * Clean up by libmultipath_exit() when the program terminates.
> + * It is an error to call libmultipath_init() after libmultipath_exit().
> + * Return: 0 on success, 1 on failure.
> + */
> +int libmultipath_init(void);
> +
> +/**
> + * libmultipath_exit() - library un-initialization
> + *
> + * This function un-initializes libmultipath data structures.
> + * It is recommended to call this function at program exit.
> + *
> + * Calls to libmultipath_init() after libmultipath_exit() will fail
> + * (in other words, libmultipath can't be re-initialized).
> + * Any other libmultipath calls after libmultipath_exit() may cause
> + * undefined behavior.
> + */
> +void libmultipath_exit(void);
>
> int find_hwe (const struct _vector *hwtable,
> const char * vendor, const char * product, const char *revision,
> diff --git a/libmultipath/debug.c b/libmultipath/debug.c
> index 4128cb9..b3a1de9 100644
> --- a/libmultipath/debug.c
> +++ b/libmultipath/debug.c
> @@ -15,6 +15,8 @@
> #include "defaults.h"
> #include "debug.h"
>
> +int logsink;
> +
> void dlog (int sink, int prio, const char * fmt, ...)
> {
> va_list ap;
> diff --git a/libmultipath/libmultipath.version b/libmultipath/libmultipath.version
> index 3e780fc..0c300c8 100644
> --- a/libmultipath/libmultipath.version
> +++ b/libmultipath/libmultipath.version
> @@ -261,3 +261,11 @@ global:
> init_config;
> uninit_config;
> } LIBMULTIPATH_2.1.0;
> +
> +LIBMULTIPATH_2.3.0 {
> +global:
> + udev;
> + logsink;
> + libmultipath_init;
> + libmultipath_exit;
> +} LIBMULTIPATH_2.2.0;
> --
> 2.28.0
--
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