[PATCH v2 1/4] common/rc: Add helper to calculate percentage of free space available

It calculates percentage of filesystem available space and returns it
in MB. This helper will be used in the following test/generic fixes.

Signed-off-by: Lukas Herbolt <[email protected]>
---
 changes v2:
	spelling and description
 common/rc | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/common/rc b/common/rc
index 5fe44e2158ff..9fc733ebdcf4 100644
--- a/common/rc
+++ b/common/rc
@@ -6189,6 +6189,16 @@ _require_fanotify_ioerrors()
 	_notrun "$FSTYP does not support fanotify ioerrors"
 }
 
+# Computes a percentage of the available space in a filesystem and
+# returns that quantity in MB. The percentage must not contain a percent
+# sign ("%").
+# usage example:
+# _mb_pct_of_available_space <mount point> <percent>
+#
+_mb_pct_of_available_space()
+{
+        _df_device $1 | $AWK_PROG -v pct=$2 '{printf "%.f", (($5*(pct/100))/1024)}'
+}
 ################################################################################
 # make sure this script returns success
 /bin/true
-- 
2.54.0