process_each_pv: do full scan earlier to find new devices

Before commit c1f246fedf,
_get_all_devices() did a full device scan before
get_vgnameids() was called.  The full scan in
_get_all_devices() is from calling dev_iter_create(f, 1).
The '1' arg forces a full scan.

By doing a full scan in _get_all_devices(), new devices
were added to dev-cache before get_vgnameids() began
scanning labels.  So, labels would be read from new devices.
(e.g. by the first 'pvs' command after the new device appeared.)

After that commit, _get_all_devices() was called
after get_vgnameids() was finished scanning labels.
So, new devices would be missed while scanning labels.
When _get_all_devices() saw the new devices (after
labels were scanned), those devices were added to
the .cache file.  This meant that the second 'pvs'
command would see the devices because they would be
in .cache.

Now, the full device scan is factored out of
_get_all_devices() and called by itself at the
start of the command so that new devices will
be known before get_vgnameids() scans labels.

lib/cache/lvmcache.c

@@ -749,6 +749,7 @@ int lvmcache_label_scan(struct cmd_context *cmd, int full_scan)
 	struct dev_iter *iter;
 	struct device *dev;
 	struct format_type *fmt;
+	int dev_count = 0;
 
 	int r = 0;
 
@@ -779,11 +780,17 @@ int lvmcache_label_scan(struct cmd_context *cmd, int full_scan)
 		goto out;
 	}
 
-	while ((dev = dev_iter_get(iter)))
+	log_very_verbose("Scanning device labels");
+
+	while ((dev = dev_iter_get(iter))) {
 		(void) label_read(dev, &label, UINT64_C(0));
+		dev_count++;
+	}
 
 	dev_iter_destroy(iter);
 
+	log_very_verbose("Scanned %d device labels", dev_count);
+
 	_has_scanned = 1;
 
 	/* Perform any format-specific scanning e.g. text files */

lib/device/dev-cache.c

@@ -1026,6 +1026,16 @@ struct device *dev_cache_get_by_devt(dev_t dev, struct dev_filter *f)
 		      f->passes_filter(f, d))) ? d : NULL;
 }
 
+void dev_cache_full_scan(struct dev_filter *f)
+{
+	if (f && f->wipe) {
+		f->wipe(f); /* might call _full_scan(1) */
+		if (!full_scan_done())
+			_full_scan(1);
+	} else
+		_full_scan(1);
+}
+
 struct dev_iter *dev_iter_create(struct dev_filter *f, int dev_scan)
 {
 	struct dev_iter *di = dm_malloc(sizeof(*di));
@@ -1037,14 +1047,8 @@ struct dev_iter *dev_iter_create(struct dev_filter *f, int dev_scan)
 
 	if (dev_scan && !trust_cache()) {
 		/* Flag gets reset between each command */
-		if (!full_scan_done()) {
-			if (f && f->wipe) {
-				f->wipe(f); /* might call _full_scan(1) */
 		if (!full_scan_done())
-					_full_scan(1);
+			dev_cache_full_scan(f);
-			} else
-				_full_scan(1);
-		}
 	} else
 		_full_scan(0);
 

lib/device/dev-cache.h

@@ -45,6 +45,7 @@ int dev_cache_check_for_open_devices(void);
 /* Trigger(1) or avoid(0) a scan */
 void dev_cache_scan(int do_scan);
 int dev_cache_has_scanned(void);
+void dev_cache_full_scan(struct dev_filter *f);
 
 int dev_cache_add_dir(const char *path);
 int dev_cache_add_loopfile(const char *path);

tools/toollib.c

@@ -3339,6 +3339,13 @@ int process_each_pv(struct cmd_context *cmd,
 	if (!only_this_vgname && !lockd_gl(cmd, "sh", 0))
 		return_ECMD_FAILED;
 
+	/*
+	 * This full scan would be done by _get_all_devices() if
+	 * it were not done here first.  It's called here first
+	 * so that get_vgnameids() will look at any new devices.
+	 */
+	dev_cache_full_scan(cmd->full_filter);
+
 	/*
 	 * Need pvid's set on all PVs before processing so that pvid's
 	 * can be compared to find duplicates while processing.