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>

1 files changed, 2 insertions, 0 deletions

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) &&