Fix the mount tests (#2269)

* Fix the mount tests

As originally written by @kamalmarhubi in #231, these tests made
clever use of Linux namespaces in order to run as unprivileged users.
However, a subsequent kernel bug broke this functionality, and it hasn't
been fixed even 6 years later.  The tests have been skipped ever since.

Get the tests to run again by removing the namespace stuff and
requiring privileges instead.  Also, remove the custom test harness.
Now Nix will be compatible with tools like cargo-nextest.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1659087

* Move the mount tests into the "test" program

Now that we aren't using namespaces, they don't need their own program.

* Use "sudo" to run tests on github workflows.

Because several of the tests require root privileges.

But don't use sudo with cross.  It fails due to a known issue upstream:
cross-rs/cross#526

.github/actions/test/action.yml

@@ -5,6 +5,11 @@ inputs:
   TARGET:
     required: true
 
+  SUDO:
+    description: 'Set it to an empty string to run the tests as the current user, leave it with the default value to test with "sudo"'
+    required: false
+    default: sudo --preserve-env=HOME 
+
   TOOL: 
     description: 'Tool used to involve the test command, can be cargo or cross'
     required: false
@@ -24,4 +29,4 @@ runs:
 
     - name: test
       shell: bash
-      run: ${{ inputs.TOOL }} test --target ${{ inputs.TARGET }} --all-features
+      run: ${{ inputs.SUDO }} $(which ${{ inputs.TOOL }}) test --target ${{ inputs.TARGET }} --all-features

.github/workflows/ci.yml

@@ -92,6 +92,7 @@ jobs:
         uses: ./.github/actions/test
         with:
           TARGET: '${{ matrix.target }}'
+          SUDO: ""
           TOOL: cross
           RUSTFLAGS: --cfg qemu -D warnings
 

Cargo.toml

@@ -99,11 +99,6 @@ path = "test/sys/test_aio_drop.rs"
 name = "test-clearenv"
 path = "test/test_clearenv.rs"
 
-[[test]]
-name = "test-mount"
-path = "test/test_mount.rs"
-harness = false
-
 [[test]]
 name = "test-prctl"
 path = "test/sys/test_prctl.rs"

test/test.rs

@@ -11,6 +11,8 @@ mod test_errno;
 mod test_fcntl;
 #[cfg(linux_android)]
 mod test_kmod;
+#[cfg(target_os = "linux")]
+mod test_mount;
 #[cfg(any(
     freebsdlike,
     target_os = "fushsia",