btrfs-progs: device usage: don't calculate slack on missing device

Print      Device slack:              0.00B
instead of Device slack:           16.00EiB

Signed-off-by: Patrik Lundquist <patrik.lundquist@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/cmds-fi-usage.c b/cmds-fi-usage.c
index 101a0c4..6c846c1 100644 (file)
--- a/cmds-fi-usage.c
+++ b/cmds-fi-usage.c
@@ -1040,6 +1040,7 @@ void print_device_sizes(struct device_info *devinfo, unsigned unit_mode)
                pretty_size_mode(devinfo->device_size, unit_mode));
        printf("   Device slack: %*s%10s\n",
                (int)(20 - strlen("Device slack")), "",
-               pretty_size_mode(devinfo->device_size - devinfo->size,
+               pretty_size_mode(devinfo->device_size > 0 ?
+                       devinfo->device_size - devinfo->size : 0,
                        unit_mode));
 }