devices file: do not clear PVID of unread devices

In a certain disconnected state, a block device is present on
the system, can be opened, reports a valid size, reports the
correct device id (wwid), and matches a devices file entry.
But, reading the device can still fail.  In this case,
device_ids_validate() was misinterpreting the read error as
the device having no data/label on it (and no PVID).
The validate function would then clear the PVID from the
devices file entry for the device, thinking that it was
fixing the devices file (making it consistent with the on disk
state.)  Fix this by not attempting to check and correct a
devices file entry that cannot be read.  Also make this case
explicit in the hints validation code (which was doing the
right thing but indirectly.)

lib/device/device.h

@@ -40,6 +40,7 @@
 #define DEV_IS_NVME		0x00040000	/* set if dev is nvme */
 #define DEV_MATCHED_USE_ID	0x00080000	/* matched an entry from cmd->use_devices */
 #define DEV_SCAN_FOUND_NOLABEL	0x00100000	/* label_scan read, passed filters, but no lvm label */
+#define DEV_SCAN_NOT_READ	0x00200000	/* label_scan not able to read dev */
 
 /*
  * Support for external device info.

lib/device/device_id.c

@@ -1746,6 +1746,13 @@ void device_ids_validate(struct cmd_context *cmd, struct dm_list *scanned_devs,
 		if (scanned_devs && !dev_in_device_list(dev, scanned_devs))
 			continue;
 
+		/*
+		 * The matched device could not be read so we do not have
+		 * the PVID from disk and cannot verify the devices file entry.
+		 */
+		if (dev->flags & DEV_SCAN_NOT_READ)
+			continue;
+
 		/*
 		 * du and dev may have been matched, but the dev could still
 		 * have been excluded by other filters during label scan.
@@ -1828,6 +1835,13 @@ void device_ids_validate(struct cmd_context *cmd, struct dm_list *scanned_devs,
 		if (scanned_devs && !dev_in_device_list(dev, scanned_devs))
 			continue;
 
+		/*
+		 * The matched device could not be read so we do not have
+		 * the PVID from disk and cannot verify the devices file entry.
+		 */
+		if (dev->flags & DEV_SCAN_NOT_READ)
+			continue;
+
 		if (!cmd->filter->passes_filter(cmd, cmd->filter, dev, "persistent")) {
 			log_warn("Devices file %s is excluded by filter: %s.",
 				 dev_name(dev), dev_filtered_reason(dev));

lib/label/hints.c

@@ -236,6 +236,7 @@ static int _touch_newhints(void)
 		return_0;
 	if (fclose(fp))
 		stack;
+	log_debug("newhints created");
 	return 1;
 }
 
@@ -506,6 +507,19 @@ int validate_hints(struct cmd_context *cmd, struct dm_list *hints)
 		if (!hint->chosen)
 			continue;
 
+		/* 
+		 * label_scan was unable to read the dev so we don't know its pvid.
+		 * Since we are unable to verify the hint is correct, it's possible
+		 * that the PVID is actually found on a different device, so don't
+		 * depend on hints. (This would also fail the following pvid check.)
+		 */
+		if (dev->flags & DEV_SCAN_NOT_READ) {
+			log_debug("Uncertain hint for unread device %d:%d %s",
+				  major(hint->devt), minor(hint->devt), dev_name(dev));
+			ret = 0;
+			continue;
+		}
+
 		if (strcmp(dev->pvid, hint->pvid)) {
 			log_debug("Invalid hint device %d:%d %s pvid %s had hint pvid %s",
 				  major(hint->devt), minor(hint->devt), dev_name(dev),

lib/label/label.c

@@ -687,6 +687,8 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 
 	dm_list_iterate_items_safe(devl, devl2, devs) {
 
+		devl->dev->flags &= ~DEV_SCAN_NOT_READ;
+
 		/*
 		 * If we prefetch more devs than blocks in the cache, then the
 		 * cache will wait for earlier reads to complete, toss the
@@ -702,6 +704,7 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 				log_debug_devs("Scan failed to open %s.", dev_name(devl->dev));
 				dm_list_del(&devl->list);
 				dm_list_add(&reopen_devs, &devl->list);
+				devl->dev->flags |= DEV_SCAN_NOT_READ;
 				continue;
 			}
 		}
@@ -725,6 +728,7 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 			log_debug_devs("Scan failed to read %s.", dev_name(devl->dev));
 			scan_read_errors++;
 			scan_failed_count++;
+			devl->dev->flags |= DEV_SCAN_NOT_READ;
 			lvmcache_del_dev(devl->dev);
 			if (bb)
 				bcache_put(bb);
@@ -1389,6 +1393,10 @@ int label_scan(struct cmd_context *cmd)
 	 * filter", and this result needs to be cleared (wiped) so that the
 	 * complete set of filters (including those that require data) can be
 	 * checked in _process_block, where headers have been read.
+	 *
+	 * FIXME: devs that are filtered with data in _process_block
+	 * are not moved to the filtered_devs list like devs filtered
+	 * here without data.  Does that have any effect?
 	 */
 	log_debug_devs("Filtering devices to scan (nodata)");