df: follow symlinks

Signed-off-by: Alexander Bakanovskii <skotttt228@gmail.com>

src/uu/df/Cargo.toml

@@ -19,7 +19,7 @@ path = "src/df.rs"
 
 [dependencies]
 clap = { workspace = true }
-uucore = { workspace = true, features = ["libc", "fsext", "parser"] }
+uucore = { workspace = true, features = ["libc", "fsext", "parser", "fs"] }
 unicode-width = { workspace = true }
 thiserror = { workspace = true }
 fluent = { workspace = true }

src/uu/df/src/df.rs

@@ -306,13 +306,24 @@ fn get_all_filesystems(opt: &Options) -> UResult<Vec<Filesystem>> {
     }
 
     let mut mounts = vec![];
-    for mi in read_fs_list()? {
+    for mut mi in read_fs_list()? {
         // TODO The running time of the `is_best()` function is linear
         // in the length of `result`. That makes the running time of
         // this loop quadratic in the length of `vmi`. This could be
         // improved by a more efficient implementation of `is_best()`,
         // but `vmi` is probably not very long in practice.
         if is_included(&mi, opt) && is_best(&mounts, &mi) {
+            let dev_path: &Path = Path::new(&mi.dev_name);
+            if dev_path.is_symlink() {
+                if let Ok(canonicalized_symlink) = uucore::fs::canonicalize(
+                    dev_path,
+                    uucore::fs::MissingHandling::Existing,
+                    uucore::fs::ResolveMode::Logical,
+                ) {
+                    mi.dev_name = canonicalized_symlink.to_string_lossy().to_string();
+                }
+            }
+
             mounts.push(mi);
         }
     }