From bf69c63e09d862eff6fdfd2bd023e3b17b1a172e Mon Sep 17 00:00:00 2001
From: Daniel Hofstetter <daniel.hofstetter@42dh.com>
Date: Fri, 1 Apr 2022 08:25:30 +0200
Subject: [PATCH] df: Fix calculation of Use% in "total" row

Change formula from: "Used/Size * 100" to "Used/(Used + Avail) * 100".
This formula also works if "Used" and "Avail" do not add up to "Size",
which is the case if there are reserved disk blocks.
---
 src/uu/df/src/table.rs   | 10 +++++++---
 tests/by-util/test_df.rs |  2 +-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/uu/df/src/table.rs b/src/uu/df/src/table.rs
index 39c762711..0f4daa0e1 100644
--- a/src/uu/df/src/table.rs
+++ b/src/uu/df/src/table.rs
@@ -102,6 +102,7 @@ impl AddAssign for Row {
     fn add_assign(&mut self, rhs: Self) {
         let bytes = self.bytes + rhs.bytes;
         let bytes_used = self.bytes_used + rhs.bytes_used;
+        let bytes_avail = self.bytes_avail + rhs.bytes_avail;
         let inodes = self.inodes + rhs.inodes;
         let inodes_used = self.inodes_used + rhs.inodes_used;
         *self = Self {
@@ -111,11 +112,14 @@ impl AddAssign for Row {
             fs_mount: "-".into(),
             bytes,
             bytes_used,
-            bytes_avail: self.bytes_avail + rhs.bytes_avail,
+            bytes_avail,
             bytes_usage: if bytes == 0 {
                 None
             } else {
-                Some(bytes_used as f64 / bytes as f64)
+                // We use "(bytes_used + bytes_avail)" instead of "bytes" because on some filesystems (e.g.
+                // ext4) "bytes" also includes reserved blocks we ignore for the usage calculation.
+                // https://www.gnu.org/software/coreutils/faq/coreutils-faq.html#df-Size-and-Used-and-Available-do-not-add-up
+                Some(bytes_used as f64 / (bytes_used + bytes_avail) as f64)
             },
             // TODO Figure out how to compute this.
             #[cfg(target_os = "macos")]
@@ -164,7 +168,7 @@ impl From<Filesystem> for Row {
                 // We use "(bused + bavail)" instead of "blocks" because on some filesystems (e.g.
                 // ext4) "blocks" also includes reserved blocks we ignore for the usage calculation.
                 // https://www.gnu.org/software/coreutils/faq/coreutils-faq.html#df-Size-and-Used-and-Available-do-not-add-up
-                Some((bused as f64) / (bused + bavail) as f64)
+                Some(bused as f64 / (bused + bavail) as f64)
             },
             #[cfg(target_os = "macos")]
             bytes_capacity: if bavail == 0 {
diff --git a/tests/by-util/test_df.rs b/tests/by-util/test_df.rs
index 2c3382ee3..b0ee8a2b3 100644
--- a/tests/by-util/test_df.rs
+++ b/tests/by-util/test_df.rs
@@ -140,7 +140,7 @@ fn test_total() {
 #[test]
 fn test_use_percentage() {
     let output = new_ucmd!()
-        .args(&["--output=used,avail,pcent"])
+        .args(&["--total", "--output=used,avail,pcent"])
         .succeeds()
         .stdout_move_str();