btrfs-progs: device scan: add new option to forget one or all scanned devices

This patch adds option --forget to 'device scan'

  $ btrfs device scan --forget [dev...]

to unregister the given device from kernel module. The device cannot be
part of a mounted filesystem, this will be reported as an error.

If no argument is given it will unregister all stale (device which are
not mounted) from the kernel.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

cmds-device.c

@@ -254,10 +254,32 @@ static int cmd_device_delete(int argc, char **argv)
 	return _cmd_device_remove(argc, argv, cmd_device_delete_usage);
 }
 
+static int btrfs_forget_devices(char *path)
+{
+	struct btrfs_ioctl_vol_args args;
+	int ret;
+	int fd;
+
+	fd = open("/dev/btrfs-control", O_RDWR);
+	if (fd < 0)
+		return -errno;
+
+	memset(&args, 0, sizeof(args));
+	if (path)
+		strncpy_null(args.name, path);
+	ret = ioctl(fd, BTRFS_IOC_FORGET_DEV, &args);
+	if (ret)
+		ret = -errno;
+	close(fd);
+	return ret;
+}
+
 static const char * const cmd_device_scan_usage[] = {
-	"btrfs device scan [(-d|--all-devices)|<device> [<device>...]]",
-	"Scan devices for a btrfs filesystem",
+	"btrfs device scan [(-d|--all-devices)|(-u|--forget)|<device> "\
+							"[<device>...]]",
+	"Scan or forget (deregister) devices for a btrfs filesystem",
 	" -d|--all-devices (deprecated)",
+	" -u|--forget [<device> ..]",
 	NULL
 };
 
@@ -267,37 +289,53 @@ static int cmd_device_scan(int argc, char **argv)
 	int devstart;
 	int all = 0;
 	int ret = 0;
+	int forget = 0;
 
 	optind = 0;
 	while (1) {
 		int c;
 		static const struct option long_options[] = {
 			{ "all-devices", no_argument, NULL, 'd'},
+			{ "forget", no_argument, NULL, 'u'},
 			{ NULL, 0, NULL, 0}
 		};
 
-		c = getopt_long(argc, argv, "d", long_options, NULL);
+		c = getopt_long(argc, argv, "du", long_options, NULL);
 		if (c < 0)
 			break;
 		switch (c) {
 		case 'd':
 			all = 1;
 			break;
+		case 'u':
+			forget = 1;
+			break;
 		default:
 			usage(cmd_device_scan_usage);
 		}
 	}
 	devstart = optind;
 
+	if (all && forget)
+		usage(cmd_device_scan_usage);
+
 	if (all && check_argc_max(argc - optind, 1))
 		usage(cmd_device_scan_usage);
 
 	if (all || argc - optind == 0) {
-		printf("Scanning for Btrfs filesystems\n");
-		ret = btrfs_scan_devices();
-		error_on(ret, "error %d while scanning", ret);
-		ret = btrfs_register_all_devices();
-		error_on(ret, "there are %d errors while registering devices", ret);
+		if (forget) {
+			ret = btrfs_forget_devices(NULL);
+			error_on(ret, "'%s', forget failed",
+				 strerror(-ret));
+		} else {
+			printf("Scanning for Btrfs filesystems\n");
+			ret = btrfs_scan_devices();
+			error_on(ret, "error %d while scanning", ret);
+			ret = btrfs_register_all_devices();
+			error_on(ret,
+				"there are %d errors while registering devices",
+				ret);
+		}
 		goto out;
 	}
 
@@ -315,11 +353,19 @@ static int cmd_device_scan(int argc, char **argv)
 			ret = 1;
 			goto out;
 		}
-		printf("Scanning for Btrfs filesystems in '%s'\n", path);
-		if (btrfs_register_one_device(path) != 0) {
-			ret = 1;
-			free(path);
-			goto out;
+		if (forget) {
+			ret = btrfs_forget_devices(path);
+			if (ret)
+				error("Can't forget '%s': %s",
+							path, strerror(-ret));
+		} else {
+			printf("Scanning for Btrfs filesystems in '%s'\n",
+									path);
+			if (btrfs_register_one_device(path) != 0) {
+				ret = 1;
+				free(path);
+				goto out;
+			}
 		}
 		free(path);
 	}

ioctl.h

@@ -814,6 +814,8 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
 				   struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \
 				   struct btrfs_ioctl_vol_args)
+#define BTRFS_IOC_FORGET_DEV _IOW(BTRFS_IOCTL_MAGIC, 5, \
+				   struct btrfs_ioctl_vol_args)
 /* trans start and trans end are dangerous, and only for
  * use by applications that know how to avoid the
  * resulting deadlocks