e2e_tests: pmem_ext2: Add a test case for many files

BUG=b:33033395
TEST=CQ

Change-Id: I276ba8276da0e39a5b6c15a903d7707ba7e79f61
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5677674
Reviewed-by: Junichi Uekawa <uekawa@chromium.org>
Reviewed-by: Takaya Saeki <takayas@chromium.org>
Commit-Queue: Keiichi Watanabe <keiichiw@chromium.org>

e2e_tests/tests/pmem_ext2.rs

@@ -8,6 +8,7 @@
 
 use std::os::unix::fs::symlink;
 
+use anyhow::bail;
 use fixture::vm::Config;
 use fixture::vm::TestVm;
 
@@ -93,3 +94,64 @@ fn pmem_ext2() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+fn set_num_files_limit(num_files: u64) -> anyhow::Result<()> {
+    let mut buf = std::mem::MaybeUninit::<libc::rlimit64>::zeroed();
+    // SAFETY: Safe because this will only modify `buf` and we check the return value.
+    let res =
+        unsafe { libc::prlimit64(0, libc::RLIMIT_NOFILE, std::ptr::null(), buf.as_mut_ptr()) };
+    if res != 0 {
+        bail!("failed to call prlimit64");
+    }
+
+    // SAFETY: Safe because the kernel guarantees that the struct is fully initialized.
+    let mut limit = unsafe { buf.assume_init() };
+    if limit.rlim_max < num_files {
+        bail!("rlim_max < num_files: {} < {}", limit.rlim_max, num_files);
+    }
+
+    limit.rlim_cur = num_files;
+    // SAFETY: Safe because limit is properly initialized.
+    let res = unsafe { libc::setrlimit64(libc::RLIMIT_NOFILE, &limit) };
+    if res != 0 {
+        bail!("failed to call setrlimit64");
+    }
+
+    Ok(())
+}
+
+/// Check a case with 1000 files in a directory.
+#[test]
+fn pmem_ext2_manyfiles() -> anyhow::Result<()> {
+    // /temp_dir/
+    // ├── 0.txt
+    // ...
+    // └── 999.txt
+
+    // TODO(crrev.com/c/5644847): Remove `set_num_files_limi` once we add a logic to fork a separate
+    // process for ext2 creation with larger files limit.
+    set_num_files_limit(2048)?;
+
+    let temp_dir = tempfile::tempdir()?;
+    for i in 0..1000 {
+        let f = temp_dir.path().join(&format!("{i}.txt"));
+        std::fs::write(f, &format!("{i}"))?;
+    }
+
+    let config = Config::new().extra_args(vec![
+        "--pmem-ext2".to_string(),
+        temp_dir.path().to_str().unwrap().to_string(),
+    ]);
+
+    let mut vm = TestVm::new(config)?;
+    vm.exec_in_guest("mount -t ext2 /dev/pmem0 /mnt/")?;
+
+    // `ls -l` returns 1002 lines because 1000 files + 'lost+found' and the total line.
+    let ls_result = vm
+        .exec_in_guest_async("ls -l /mnt/ | wc -l")?
+        .with_timeout(std::time::Duration::from_secs(1))
+        .wait_ok(&mut vm)?;
+    assert_eq!(ls_result.stdout.trim(), "1002");
+
+    Ok(())
+}