Re: [PATCH 10/19] libmultipath: devmapper: refactor libdm version determination

[Benjamin Marzinski <bmarzins@redhat.com>]

On Wed, Sep 16, 2020 at 05:37:09PM +0200, mwilck@suse.com wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> As one step towards bundling all possibly racy libdm init calls into a single
> function, split the code for determining and checking versions of
> libdm and kernel components. Provide a generic helper
> libmp_get_version() that makes sure the versions are "lazily" initialized.
> Note that retrieving the versions requires libdm calls, thus the
> version initialization calls libdm initialization, which might call
> version initialization recursively. But that's not an issue, as
> the initialization is protected by pthread_once().

This is confusing me. dm_tgt_version will call DM_DEVICE_LIST_VERSIONS,
but it doesn't call libmp_dm_task_create(), so I don't see the recursion
possiblity. That's good because according to the man page:

"If you specify a routine that directly or indirectly results in a
recursive call to pthread_once(3) and that specifies the same routine
argument, the recursive call can result in a deadlock."

-Ben
 
> External callers may use dm_prereq(), like before.
> Minor API change: dm_prereq() does not nullify the argument any more
> if an error is encountered.
> 
> Remove the conf->version field, which isn't needed any more after this
> change.
> 
> Cc: lixiaokeng@huawei.com
> Cc: Zdenek Kabelac <zkabelac@redhat.com>
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  libmultipath/config.h    |   1 -
>  libmultipath/devmapper.c | 155 ++++++++++++++++++++++++++-------------
>  libmultipath/devmapper.h |  11 ++-
>  libmultipath/propsel.c   |  10 ++-
>  multipathd/dmevents.c    |   2 +-
>  multipathd/main.c        |   1 -
>  6 files changed, 120 insertions(+), 60 deletions(-)
> 
> diff --git a/libmultipath/config.h b/libmultipath/config.h
> index 2bb7153..8e13ae9 100644
> --- a/libmultipath/config.h
> +++ b/libmultipath/config.h
> @@ -191,7 +191,6 @@ struct config {
>  	int find_multipaths_timeout;
>  	int marginal_pathgroups;
>  	int skip_delegate;
> -	unsigned int version[3];
>  	unsigned int sequence_nr;
>  
>  	char * multipath_dir;
> diff --git a/libmultipath/devmapper.c b/libmultipath/devmapper.c
> index cc2de1d..3694cc8 100644
> --- a/libmultipath/devmapper.c
> +++ b/libmultipath/devmapper.c
> @@ -26,6 +26,7 @@
>  #include "sysfs.h"
>  #include "config.h"
>  #include "wwids.h"
> +#include "version.h"
>  
>  #include "log_pthread.h"
>  #include <sys/types.h>
> @@ -34,7 +35,13 @@
>  #define MAX_WAIT 5
>  #define LOOPS_PER_SEC 5
>  
> +#define INVALID_VERSION ~0U
> +static unsigned int dm_library_version[3] = { INVALID_VERSION, };
> +static unsigned int dm_kernel_version[3] = { INVALID_VERSION, };
> +static unsigned int dm_mpath_target_version[3] = { INVALID_VERSION, };
> +
>  static pthread_once_t dm_initialized = PTHREAD_ONCE_INIT;
> +static pthread_once_t versions_initialized = PTHREAD_ONCE_INIT;
>  
>  static int dm_conf_verbosity;
>  
> @@ -102,7 +109,7 @@ dm_write_log (int level, const char *file, int line, const char *f, ...)
>  	return;
>  }
>  
> -void dm_init(int v)
> +static void dm_init(int v)
>  {
>  	/*
>  	 * This maps libdm's standard loglevel _LOG_WARN (= 4), which is rather
> @@ -112,59 +119,66 @@ void dm_init(int v)
>  	dm_log_init(&dm_write_log);
>  }
>  
> +static void init_dm_library_version(void)
> +{
> +	char version[64];
> +	unsigned int v[3];
> +
> +	dm_get_library_version(version, sizeof(version));
> +	if (sscanf(version, "%u.%u.%u ", &v[0], &v[1], &v[2]) != 3) {
> +		condlog(0, "invalid libdevmapper version %s", version);
> +		return;
> +	}
> +	memcpy(dm_library_version, v, sizeof(dm_library_version));
> +	condlog(3, "libdevmapper version %u.%.2u.%.2u",
> +		dm_library_version[0], dm_library_version[1],
> +		dm_library_version[2]);
> +}
> +
>  static int
>  dm_lib_prereq (void)
>  {
> -	char version[64];
> -	int v[3];
> +
>  #if defined(LIBDM_API_HOLD_CONTROL)
> -	int minv[3] = {1, 2, 111};
> +	unsigned int minv[3] = {1, 2, 111};
>  #elif defined(LIBDM_API_DEFERRED)
> -	int minv[3] = {1, 2, 89};
> +	unsigned int minv[3] = {1, 2, 89};
>  #elif defined(DM_SUBSYSTEM_UDEV_FLAG0)
> -	int minv[3] = {1, 2, 82};
> +	unsigned int minv[3] = {1, 2, 82};
>  #elif defined(LIBDM_API_COOKIE)
> -	int minv[3] = {1, 2, 38};
> +	unsigned int minv[3] = {1, 2, 38};
>  #else
> -	int minv[3] = {1, 2, 8};
> +	unsigned int minv[3] = {1, 2, 8};
>  #endif
>  
> -	dm_get_library_version(version, sizeof(version));
> -	condlog(3, "libdevmapper version %s", version);
> -	if (sscanf(version, "%d.%d.%d ", &v[0], &v[1], &v[2]) != 3) {
> -		condlog(0, "invalid libdevmapper version %s", version);
> -		return 1;
> -	}
> -
> -	if VERSION_GE(v, minv)
> +	if (VERSION_GE(dm_library_version, minv))
>  		return 0;
> -	condlog(0, "libdevmapper version must be >= %d.%.2d.%.2d",
> +	condlog(0, "libdevmapper version must be >= %u.%.2u.%.2u",
>  		minv[0], minv[1], minv[2]);
>  	return 1;
>  }
>  
> -int
> -dm_drv_version(unsigned int *v)
> +static void init_dm_drv_version(void)
>  {
>  	char buff[64];
> -
> -	v[0] = 0;
> -	v[1] = 0;
> -	v[2] = 0;
> +	unsigned int v[3];
>  
>  	if (!dm_driver_version(buff, sizeof(buff))) {
>  		condlog(0, "cannot get kernel dm version");
> -		return 1;
> +		return;
>  	}
>  	if (sscanf(buff, "%u.%u.%u ", &v[0], &v[1], &v[2]) != 3) {
>  		condlog(0, "invalid kernel dm version '%s'", buff);
> -		return 1;
> +		return;
>  	}
> -	return 0;
> +	memcpy(dm_kernel_version, v, sizeof(dm_library_version));
> +	condlog(3, "kernel device mapper v%u.%u.%u",
> +		dm_kernel_version[0],
> +		dm_kernel_version[1],
> +		dm_kernel_version[2]);
>  }
>  
> -int
> -dm_tgt_version (unsigned int * version, char * str)
> +static int dm_tgt_version (unsigned int *version, char *str)
>  {
>  	int r = 2;
>  	struct dm_task *dmt;
> @@ -172,10 +186,6 @@ dm_tgt_version (unsigned int * version, char * str)
>  	struct dm_versions *last_target;
>  	unsigned int *v;
>  
> -	version[0] = 0;
> -	version[1] = 0;
> -	version[2] = 0;
> -
>  	if (!(dmt = dm_task_create(DM_DEVICE_LIST_VERSIONS)))
>  		return 1;
>  
> @@ -211,26 +221,25 @@ out:
>  	return r;
>  }
>  
> -static int
> -dm_tgt_prereq (unsigned int *ver)
> +static void init_dm_mpath_version(void)
>  {
> -	unsigned int minv[3] = {1, 0, 3};
> -	unsigned int version[3] = {0, 0, 0};
> -	unsigned int * v = version;
> -
> -	if (dm_tgt_version(v, TGT_MPATH)) {
> -		/* in doubt return not capable */
> -		return 1;
> -	}
> -
> -	/* test request based multipath capability */
> +	dm_tgt_version(dm_mpath_target_version, TGT_MPATH);
>  	condlog(3, "DM multipath kernel driver v%u.%u.%u",
> -		v[0], v[1], v[2]);
> +		dm_mpath_target_version[0],
> +		dm_mpath_target_version[1],
> +		dm_mpath_target_version[2]);
> +}
> +
> +static int dm_tgt_prereq (unsigned int *ver)
> +{
> +	unsigned int minv[3] = {1, 0, 3};
>  
> -	if (VERSION_GE(v, minv)) {
> -		ver[0] = v[0];
> -		ver[1] = v[1];
> -		ver[2] = v[2];
> +	if (VERSION_GE(dm_mpath_target_version, minv)) {
> +		if (ver) {
> +			ver[0] = dm_mpath_target_version[0];
> +			ver[1] = dm_mpath_target_version[1];
> +			ver[2] = dm_mpath_target_version[2];
> +		}
>  		return 0;
>  	}
>  
> @@ -239,13 +248,60 @@ dm_tgt_prereq (unsigned int *ver)
>  	return 1;
>  }
>  
> +static void _init_versions(void)
> +{
> +	dlog(logsink, 3, VERSION_STRING);
> +	init_dm_library_version();
> +	init_dm_drv_version();
> +	init_dm_mpath_version();
> +}
> +
> +static int init_versions(void) {
> +	pthread_once(&versions_initialized, _init_versions);
> +	return (dm_library_version[0] == INVALID_VERSION ||
> +		dm_kernel_version[0] == INVALID_VERSION ||
> +		dm_mpath_target_version[0] == INVALID_VERSION);
> +}
> +
>  int dm_prereq(unsigned int *v)
>  {
> +	if (init_versions())
> +		return 1;
>  	if (dm_lib_prereq())
>  		return 1;
>  	return dm_tgt_prereq(v);
>  }
>  
> +int libmp_get_version(int which, unsigned int version[3])
> +{
> +	unsigned int *src_version;
> +
> +	init_versions();
> +	switch (which) {
> +	case DM_LIBRARY_VERSION:
> +		src_version = dm_library_version;
> +		break;
> +	case DM_KERNEL_VERSION:
> +		src_version = dm_kernel_version;
> +		break;
> +	case DM_MPATH_TARGET_VERSION:
> +		src_version = dm_mpath_target_version;
> +		break;
> +	case MULTIPATH_VERSION:
> +		version[0] = (VERSION_CODE >> 16) & 0xff;
> +		version[1] = (VERSION_CODE >> 8) & 0xff;
> +		version[2] = VERSION_CODE & 0xff;
> +		return 0;
> +	default:
> +		condlog(0, "%s: invalid value for 'which'", __func__);
> +		return 1;
> +	}
> +	if (src_version[0] == INVALID_VERSION)
> +		return 1;
> +	memcpy(version, src_version, 3 * sizeof(*version));
> +	return 0;
> +}
> +
>  static int libmp_dm_udev_sync = 0;
>  
>  void libmp_udev_set_sync_support(int on)
> @@ -263,7 +319,6 @@ static void libmp_dm_init(void)
>  		exit(1);
>  	conf = get_multipath_config();
>  	verbosity = conf->verbosity;
> -	memcpy(conf->version, version, sizeof(version));
>  	put_multipath_config(conf);
>  	dm_init(verbosity);
>  #ifdef LIBDM_API_HOLD_CONTROL
> diff --git a/libmultipath/devmapper.h b/libmultipath/devmapper.h
> index f568ab5..c8b37e1 100644
> --- a/libmultipath/devmapper.h
> +++ b/libmultipath/devmapper.h
> @@ -33,13 +33,10 @@ enum {
>  	DMP_NOT_FOUND,
>  };
>  
> -void dm_init(int verbosity);
>  int dm_prereq(unsigned int *v);
>  void skip_libmp_dm_init(void);
>  void libmp_udev_set_sync_support(int on);
>  struct dm_task *libmp_dm_task_create(int task);
> -int dm_drv_version (unsigned int * version);
> -int dm_tgt_version (unsigned int * version, char * str);
>  int dm_simplecmd_flush (int, const char *, uint16_t);
>  int dm_simplecmd_noflush (int, const char *, uint16_t);
>  int dm_addmap_create (struct multipath *mpp, char *params);
> @@ -85,6 +82,14 @@ struct multipath *dm_get_multipath(const char *name);
>  	((v[0] == minv[0]) && (v[1] == minv[1]) && (v[2] >= minv[2])) \
>  )
>  
> +enum {
> +	DM_LIBRARY_VERSION,
> +	DM_KERNEL_VERSION,
> +	DM_MPATH_TARGET_VERSION,
> +	MULTIPATH_VERSION
> +};
> +int libmp_get_version(int which, unsigned int version[3]);
> +
>  #define dm_log_error(lvl, cmd, dmt)			      \
>  	condlog(lvl, "%s: libdm task=%d error: %s", __func__, \
>  		cmd, strerror(dm_task_get_errno(dmt)))	      \
> diff --git a/libmultipath/propsel.c b/libmultipath/propsel.c
> index 7e6e0d6..781515e 100644
> --- a/libmultipath/propsel.c
> +++ b/libmultipath/propsel.c
> @@ -737,9 +737,10 @@ out:
>  
>  int select_minio(struct config *conf, struct multipath *mp)
>  {
> -	unsigned int minv_dmrq[3] = {1, 1, 0};
> +	unsigned int minv_dmrq[3] = {1, 1, 0}, version[3];
>  
> -	if (VERSION_GE(conf->version, minv_dmrq))
> +	if (!libmp_get_version(DM_MPATH_TARGET_VERSION, version)
> +	    && VERSION_GE(version, minv_dmrq))
>  		return select_minio_rq(conf, mp);
>  	else
>  		return select_minio_bio(conf, mp);
> @@ -822,9 +823,10 @@ out:
>  int select_retain_hwhandler(struct config *conf, struct multipath *mp)
>  {
>  	const char *origin;
> -	unsigned int minv_dm_retain[3] = {1, 5, 0};
> +	unsigned int minv_dm_retain[3] = {1, 5, 0}, version[3];
>  
> -	if (!VERSION_GE(conf->version, minv_dm_retain)) {
> +	if (!libmp_get_version(DM_MPATH_TARGET_VERSION, version) &&
> +	    !VERSION_GE(version, minv_dm_retain)) {
>  		mp->retain_hwhandler = RETAIN_HWHANDLER_OFF;
>  		origin = "(setting: WARNING, requires kernel dm-mpath version >= 1.5.0)";
>  		goto out;
> diff --git a/multipathd/dmevents.c b/multipathd/dmevents.c
> index 5f2d210..fc97c8a 100644
> --- a/multipathd/dmevents.c
> +++ b/multipathd/dmevents.c
> @@ -60,7 +60,7 @@ int dmevent_poll_supported(void)
>  {
>  	unsigned int v[3];
>  
> -	if (dm_drv_version(v))
> +	if (libmp_get_version(DM_KERNEL_VERSION, v))
>  		return 0;
>  
>  	if (VERSION_GE(v, DM_VERSION_FOR_ARM_POLL))
> diff --git a/multipathd/main.c b/multipathd/main.c
> index affe706..53bacac 100644
> --- a/multipathd/main.c
> +++ b/multipathd/main.c
> @@ -2719,7 +2719,6 @@ reconfigure (struct vectors * vecs)
>  	/* Re-read any timezone changes */
>  	tzset();
>  
> -	dm_tgt_version(conf->version, TGT_MPATH);
>  	if (verbosity)
>  		conf->verbosity = verbosity;
>  	if (bindings_read_only)
> -- 
> 2.28.0