test: fix tests for newer kernels

The ubuntu-latest kernel now has a 6.2 kernel. That makes the creation
of a new userfault file descriptor to use path that creates the fd
issuing an ioctl to /dev/userfaultfd. However, in our Github action
/dev/userfaultfd is read/write only by root whereas the job is running
as the "runner" user. This causes the tests to fail, because they can't
open the device file to issue the ioctl.

This commit does two things. First it creates a test matrix so that we
run the github action both on ubuntu-latest (with a newer kerenl) and
ubuntu-20.04 that uses a 5.15 kernel. That ensures that we test both
file descriptor creation paths (/dev/userfaultfd and userfaultfd
syscall). Second, in the case of ubuntu-latest it gives to the "runner"
user access to /dev/userfaultfd file.

Signed-off-by: Babis Chalios <[email protected]>

Author: bchalios

.github/workflows/rust.yml

@@ -9,24 +9,50 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    # ubuntu-latest runs a recent kernel with /dev/userfaultfd support whereas
+    # ubuntu-20.04 has a 5.15 kernel. We run the job in both, so we can test
+    # both paths for creating the file descriptor, i.e. /dev/userfaultfd ioctl
+    # and userfaultfd syscall.
+    runs-on: ${{ matrix.runner }}
+    strategy:
+      matrix:
+        runner: [ ubuntu-latest, ubuntu-20.04 ]
 
     steps:
     - uses: actions/checkout@v2
+
+    # Keep this step, so that we can check that the Linux kernel is the one we
+    # expect, depending on the runner kernel.
+    - name: Check Linux version
+      run: uname -r
+
+    # /dev/userfaultfd is only present on ubuntu-latest.
+    - name: Setup access to /dev/userfaultfd
+      if: ${{ matrix.runner == 'ubuntu-latest' }}
+      run: sudo setfacl -m u:${USER}:rw /dev/userfaultfd
+
     - name: Build
       run: cargo build --verbose
 
-    # The github ubuntu-latest is now on linux 5.11 kernel,
-    # so we can test the crate with support for each of the
-    # kernel featuresets:
-
     - name: Run tests (Linux 4.11 support)
       run: cargo test --verbose
     - name: Run tests (Linux 4.14 support)
       run: cargo test --verbose --features linux4_14
+
     - name: Run tests (Linux 5.7 support)
+      if: ${{ matrix.runner == 'ubuntu-latest' }}
       run: cargo test --verbose --features linux5_7
 
+    # On ubuntu-20.04 runner we need to make sure we have the proper kernel
+    # headers for building the correct bindings
+    - name: Run tests (Linux 5.7 support)
+      if: ${{ matrix.runner == 'ubuntu-20.04' }}
+      run:
+        sudo apt update &&
+        sudo apt install -y linux-headers-5.11.0-25-generic &&
+        export LINUX_HEADERS=/usr/src/linux-headers-5.11.0-25-generic &&
+        cargo test --verbose --features linux5_7
+
   audit:
 
     runs-on: ubuntu-latest