Re: [PATCH v4 16/20] multipath -u : set FIND_MULTIPATHS_WAIT_UNTIL from /dev/shm

["Benjamin Marzinski" <bmarzins@redhat.com>]

On Wed, Apr 04, 2018 at 06:16:23PM +0200, Martin Wilck wrote:
> In "find_multipaths smart" mode, use time stamps under
> /dev/shm/multipath/find_multipaths to track waiting for multipath
> siblings. When a path is first encountered and is "maybe" multipath, create a
> file under /dev/shm, set its modification time to the expiry time of the
> timer, and set the FIND_MULTIPATHS_WAIT_UNTIL variable. On later calls, also set
> FIND_MULTIPATHS_WAIT_UNTIL to the expiry time (but don't change the time
> stamp) if it's not expired yet, or 0 if it is expired. Set
> FIND_MULTIPATHS_WAIT_UNTIL even if enough evidence becomes available to decide
> if the path needs to be multipathed - this enables the udev rules to detect
> that this is a device a timer has been started for, and stop it. By using
> /dev/shm, we share information about "smart" timers between initrd and root
> file system, and thus only calculate the timeout once.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  libmultipath/file.c |   2 +-
>  libmultipath/file.h |   1 +
>  multipath/main.c    | 133 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 135 insertions(+), 1 deletion(-)
> 
> diff --git a/libmultipath/file.c b/libmultipath/file.c
> index d5165ec..8727f16 100644
> --- a/libmultipath/file.c
> +++ b/libmultipath/file.c
> @@ -36,7 +36,7 @@
>   * See the file COPYING included with this distribution for more details.
>   */
>  
> -static int
> +int
>  ensure_directories_exist(const char *str, mode_t dir_mode)
>  {
>  	char *pathname;
> diff --git a/libmultipath/file.h b/libmultipath/file.h
> index 70bffa5..29520c7 100644
> --- a/libmultipath/file.h
> +++ b/libmultipath/file.h
> @@ -6,6 +6,7 @@
>  #define _FILE_H
>  
>  #define FILE_TIMEOUT 30
> +int ensure_directories_exist(const char *str, mode_t dir_mode);
>  int open_file(const char *file, int *can_write, const char *header);
>  
>  #endif /* _FILE_H */
> diff --git a/multipath/main.c b/multipath/main.c
> index f62e18a..126f90f 100644
> --- a/multipath/main.c
> +++ b/multipath/main.c
> @@ -29,6 +29,7 @@
>  #include <ctype.h>
>  #include <libudev.h>
>  #include <syslog.h>
> +#include <fcntl.h>
>  
>  #include "checkers.h"
>  #include "prio.h"
> @@ -60,6 +61,9 @@
>  #include "uxsock.h"
>  #include "mpath_cmd.h"
>  #include "foreign.h"
> +#include "propsel.h"
> +#include "time-util.h"
> +#include "file.h"
>  
>  int logsink;
>  struct udev *udev;
> @@ -350,14 +354,143 @@ out:
>  	return r;
>  }
>  
> +enum {
> +	FIND_MULTIPATHS_WAIT_DONE = 0,
> +	FIND_MULTIPATHS_WAITING = 1,
> +	FIND_MULTIPATHS_ERROR = -1,
> +	FIND_MULTIPATHS_NEVER = -2,
> +};
> +
> +static const char shm_find_mp_dir[] = MULTIPATH_SHM_BASE "find_multipaths";
> +static void close_fd(void* arg)
> +{
> +	close((long)arg);
> +}
> +
> +/**
> + * find_multipaths_check_timeout(wwid, tmo)
> + * Helper for "find_multipaths smart"
> + *
> + * @param[in] pp: path to check / record
> + * @param[in] tmo: configured timeout for this WWID, or value <= 0 for checking
> + * @param[out] until: timestamp until we must wait, CLOCK_REALTIME, if return
> + *             value is FIND_MULTIPATHS_WAITING
> + * @returns: FIND_MULTIPATHS_WAIT_DONE, if waiting has finished
> + * @returns: FIND_MULTIPATHS_ERROR, if internal error occured
> + * @returns: FIND_MULTIPATHS_NEVER, if tmo is 0 and we didn't wait for this
> + *           device
> + * @returns: FIND_MULTIPATHS_WAITING, if timeout hasn't expired
> + */
> +static int find_multipaths_check_timeout(const struct path *pp, long tmo,
> +					 struct timespec *until)
> +{
> +	char path[PATH_MAX];
> +	struct timespec now, ftimes[2], tdiff;
> +	struct stat st;
> +	long fd;
> +	int r, err, retries = 0;
> +
> +	clock_gettime(CLOCK_REALTIME, &now);
> +

I'm worried about using pp->dev_t here with no method of removing these
files.  What happens when a path device, say 8:32 is removed and a
completely new device comes in reusing the same dev_t?

> +	if (snprintf(path, sizeof(path), "%s/%s", shm_find_mp_dir, pp->dev_t)
> +	    >= sizeof(path)) {
> +		condlog(1, "%s: path name overflow", __func__);

shouldn't this be:
		return FIND_MULTIPATHS_ERROR;

> +		return -1;
> +	}
> +
> +	if (ensure_directories_exist(path, 0700)) {
> +		condlog(1, "%s: error creating directories", __func__);
> +		return FIND_MULTIPATHS_ERROR;
> +	}
> +
> +retry:
> +	fd = open(path, O_RDONLY);
> +	if (fd != -1) {
> +		pthread_cleanup_push(close_fd, (void*)fd);
> +		r = fstat(fd, &st);
> +		if (r != 0)
> +			err = errno;
> +		pthread_cleanup_pop(1);
> +
> +	} else if (tmo > 0) {
> +		if (errno == ENOENT)
> +			fd = open(path, O_RDWR|O_EXCL|O_CREAT, 0644);
> +		if (fd == -1) {
> +			if (errno == EEXIST && !retries++)
> +				/* We could have raced with another process */
> +				goto retry;
> +			condlog(1, "%s: error opening %s: %s",
> +				__func__, path, strerror(errno));
> +			return FIND_MULTIPATHS_ERROR;
> +		};
> +
> +		pthread_cleanup_push(close_fd, (void*)fd);
> +		/*
> +		 * We just created the file. Set st_mtim to our desired
> +		 * expiry time.
> +		 */
> +		ftimes[0].tv_sec = 0;
> +		ftimes[0].tv_nsec = UTIME_OMIT;
> +		ftimes[1].tv_sec = now.tv_sec + tmo;
> +		ftimes[1].tv_nsec = now.tv_nsec;
> +		if (futimens(fd, ftimes) != 0) {
> +			condlog(1, "%s: error in futimens(%s): %s", __func__,
> +				path, strerror(errno));
> +		}
> +		r = fstat(fd, &st);
> +		if (r != 0)
> +			err = errno;
> +		pthread_cleanup_pop(1);
> +	} else
> +		return FIND_MULTIPATHS_NEVER;
> +
> +	if (r != 0) {
> +		condlog(1, "%s: error in fstat for %s: %s", __func__,
> +			path, strerror(err));
> +		return FIND_MULTIPATHS_ERROR;
> +	}
> +
> +	timespecsub(&st.st_mtim, &now, &tdiff);
> +
> +	if (tdiff.tv_sec <= 0)
> +		return FIND_MULTIPATHS_WAIT_DONE;
> +	else {
> +		*until = tdiff;
> +		return FIND_MULTIPATHS_WAITING;
> +	}
> +}
> +
>  static int print_cmd_valid(int k, const vector pathvec,
>  			   struct config *conf)
>  {
>  	static const int vals[] = { 1, 0, 2 };
> +	int wait = FIND_MULTIPATHS_NEVER;
> +	struct timespec until;
> +	struct path *pp;
>  
>  	if (k < 0 || k >= sizeof(vals))
>  		return 1;
>  
> +	if (k == 2) {
> +		/*
> +		 * Caller ensures that pathvec[0] is the path to
> +		 * examine.
> +		 */
> +		pp = VECTOR_SLOT(pathvec, 0);
> +		select_find_multipaths_timeout(conf, pp);
> +		wait = find_multipaths_check_timeout(
> +			pp, pp->find_multipaths_timeout, &until);
> +		if (wait != FIND_MULTIPATHS_WAITING)
> +			k = 1;
> +	} else if (pathvec != NULL) {
> +		pp = VECTOR_SLOT(pathvec, 0);
> +		wait = find_multipaths_check_timeout(pp, 0, &until);
> +	}
> +	if (wait == FIND_MULTIPATHS_WAITING)
> +		printf("FIND_MULTIPATHS_WAIT_UNTIL=\"%ld.%06ld\"\n",
> +			       until.tv_sec, until.tv_nsec/1000);
> +	else if (wait == FIND_MULTIPATHS_WAIT_DONE)
> +		printf("FIND_MULTIPATHS_WAIT_UNTIL=\"0\"\n");

If we get an error trying to check the timeout, should we just keep
FIND_MULTIPATHS_WAIT_UNTIL the same? Or would it be better to set it to
0, and fail the smart claiming?

>  	printf("DM_MULTIPATH_DEVICE_PATH=\"%d\"\n", vals[k]);
>  	return k == 1;
>  }
> -- 
> 2.16.1