btrfs-progs: dump-tree: print invalid argument and strerror

Before this patch:

  $ ls nothingness
  ls: cannot access 'nothingness': No such file or directory
  $ btrfs inspect-internal dump-tree nothingness
  ERROR: not a block device or regular file: nothingness

The confusing error message makes users think that nonexistent file
exiss but is of a wrong type.

This patch lets check_arg_type return -errno if realpath failed.  And
print strerror if check_arg_type failed and the returned code is
negative. Like:

  $ btrfs inspect-internal dump-tree nothingness
  ERROR: invalid argument: nothingness: No such file or directory

Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

2 files changed, 8 insertions, 1 deletions

diff --git a/cmds-inspect-dump-tree.c b/cmds-inspect-dump-tree.c
index c8acd55a..d84d52dd 100644
--- a/cmds-inspect-dump-tree.c
+++ b/cmds-inspect-dump-tree.c
@@ -313,7 +313,12 @@ int cmd_inspect_dump_tree(int argc, char **argv)
 
 	ret = check_arg_type(argv[optind]);
 	if (ret != BTRFS_ARG_BLKDEV && ret != BTRFS_ARG_REG) {
-		error("not a block device or regular file: %s", argv[optind]);
+		if (ret < 0)
+			error("invalid argument %s: %s", argv[optind],
+			      strerror(-ret));
+		else
+			error("not a block device or regular file: %s",
+			      argv[optind]);
 		goto out;
 	}
 
diff --git a/utils.c b/utils.c
index d4395b1f..785c2022 100644
--- a/utils.c
+++ b/utils.c
@@ -502,6 +502,8 @@ int check_arg_type(const char *input)
 			return BTRFS_ARG_REG;
 
 		return BTRFS_ARG_UNKNOWN;
+	} else {
+		return -errno;
 	}
 
 	if (strlen(input) == (BTRFS_UUID_UNPARSED_SIZE - 1) &&