[dm-devel] [PATCH] multipathd: warn when configuration has been changed.

[Martin Wilck]

On Mon, 2019-09-23 at 14:29 -0500, Benjamin Marzinski wrote:
> It would be helpful if multipathd could log a message when
> multipath.conf or files in the config_dir have been written to, both
> so
> that it can be used to send a notification to users, and to help with
> determining after the fact if multipathd was running with an older
> config, when the logs of multipathd's behaviour don't match with the
> current multipath.conf.
> 
> To do this, the multipathd uxlsnr thread now sets up inotify watches
> on
> both /etc/multipath.conf and the config_dir to watch if the files are
> deleted or closed after being opened for writing.  In order to keep
> uxlsnr from polling repeatedly if the multipath.conf or the
> config_dir
> aren't present, it will only set up the watches once per reconfigure.
> However, since multipath.conf is far more likely to be replaced by a
> text editor than modified in place, if it gets removed, multipathd
> will
> immediately try to restart the watch on it (which will succeed if the
> file was simply replaced by a new copy).  This does mean that if
> multipath.conf or the config_dir are actually removed and then later
> re-added, multipathd won't log any more messages for changes until
> the
> next reconfigure. But that seems like a fair trade-off to avoid
> repeatedly polling for files that aren't likely to appear.
> 
> Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
> ---
>  libmultipath/config.h |   1 +
>  multipathd/main.c     |   1 +
>  multipathd/uxlsnr.c   | 134
> ++++++++++++++++++++++++++++++++++++++++--
>  3 files changed, 130 insertions(+), 6 deletions(-)
> 

So, next, after we get a notification, we wait a few seconds and call
reconfigure() automatically? Well I guess before we do that we should
implement a dry-run with a syntax check...

I found one minor issue, see below. Otherwise, ACK.

Thanks,
Martin

> +void handle_inotify(int fd, int  *wds)
> +{
> +	char buff[1024]
> +		__attribute__ ((aligned(__alignof__(struct
> inotify_event))));
> +	const struct inotify_event *event;
> +	ssize_t len;
> +	char *ptr;
> +	int i, got_notify = 0;
> +
> +	for (;;) {
> +		len = read(fd, buff, sizeof(buff));
> +		if (len <= 0) {
> +			if (len < 0 && errno != EAGAIN) {
> +				condlog(3, "error reading from
> inotify_fd");
> +				for (i = 0; i < 2; i++) {
> +					if (wds[i] != -1) {
> +						inotify_rm_watch(fd,
> wds[0]);

Should this be wds[i] instead?