Fix FDs becoming invalid once their file is unlinked

[Arshia001]

Fixes: #6360.

[Copilot]

Pull request overview

Fixes cases where unlinking a file could invalidate existing open handles (FDs), aligning VirtualFile::unlink() behavior with expected POSIX-like semantics (path removed, handle remains usable until last close).

Changes:

• Add lifecycle tracking to mem_fs inodes so unlinked files remain backed while handles are open, and are reclaimed on last-handle drop.
• Adjust overlay_fs to support unlinking files opened from secondaries without breaking the open handle, including COW/unlink interactions.
• Add new regression tests (Rust unit tests + WASIX C test + harness script) covering write/read after unlink.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/wasix/unlink-open-fd-write-after-unlink/run.sh	Adds a WASIX test runner asserting expected stdout and host-volume behavior.
tests/wasix/unlink-open-fd-write-after-unlink/main.c	New WASIX regression reproducer verifying handle validity across unlink + recreate.
lib/virtual-fs/src/overlay_fs.rs	Adds SecondaryFile wrapper and updates COW unlink behavior; adds overlay-specific regression tests.
lib/virtual-fs/src/mem_fs/mod.rs	Introduces FileLifecycle and threads it through inode node types.
lib/virtual-fs/src/mem_fs/filesystem.rs	Centralizes unlink behavior via unlink_file_inode and updates tests for unlinked-but-open retention.
lib/virtual-fs/src/mem_fs/file_opener.rs	Plumbs lifecycle into opened handles and newly created nodes.
lib/virtual-fs/src/mem_fs/file.rs	Tracks handle open/close and reclaims storage on last-handle drop after unlink; expands tests.
lib/virtual-fs/src/lib.rs	Clarifies VirtualFile::unlink() semantics in trait documentation.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

[syrusakbary]

@theduke will be better at reviewing this

[theduke]

I found two correctness issues in the new overlay unlink handling.

[artemyarulin]

This PR seems like fixing that as well #6431

[artemyarulin]

@Arshia001 can you add a few unit tests to avoid regressions?

Here one Wasix (i've just created it before I've remembered about your PR :))

#include <assert.h>
#include <fcntl.h>
#include <unistd.h>

int main(void) {
  const char* path = "/tmp/wasix_fd_append_create_unlink_read.tmp";
  unlink(path);
  int fd = open(path, O_RDWR | O_APPEND | O_CREAT, 0600);
  assert(fd >= 0);
  assert(unlink(path) == 0);
  char buf;
  assert(read(fd, &buf, 1) == 0);
}

And the a second one from #6431 (probably need to be converted to C). It's important to have those to avoid future regressions

[artemyarulin]

Shield - Regression 💩💩💩

Language	Tests	Pass rate now	PASS	FAIL	TIMEOUT	CRASH
Python	37,920	0.0%	$${\color{red}-26105}$$	$${\color{red}+33083}$$	$${\color{green}-4911}$$	$${\color{green}-2}$$
Node.js	4,861	33.0%	$${\color{green}+18}$$	$${\color{green}-70}$$	$${\color{red}+62}$$	$${\color{green}-9}$$
PHP	19,912	72.5%	$${\color{red}-2}$$	$${\color{red}+2}$$	0	0
Rust	22,337	94.3%	$${\color{red}-1}$$	$${\color{green}-3}$$	0	$${\color{red}+2}$$

Example crash from Rust

• Repro command: shield run --lang rust --wasmer [WASMER BINARY] library::coretests::coretests-c583afeaf1b1870c
• Full status file: tests_rust_results.json

crash: process: proc=000127 cwd=/home/runner/work/anti-regression-shield/anti-regression-shield env=RUST_BACKTRACE=full command=/home/runner/work/anti-regression-shield/anti-regression-shield/.work/wasmer/checkout/target/release/wasmer run --volume /home/runner/work/anti-regression-shield/anti-regression-shield/.work/rust/checkout:/home/runner/work/anti-regression-shield/anti-regression-shield/.work/rust/checkout --cwd /home/runner/work/anti-regression-shield/anti-regression-shield/.work/rust/checkout /home/runner/work/anti-regression-shield/anti-regression-shield/.cache/rust/wasmu/57fa1a714b832328.wasmu -- --test-threads=1
RuntimeError: unaligned atomic access
    at core::sync::atomic::AtomicBool::fetch_nand (coretests-3d2262867062fa53.wasm[14495]:0xffffffff)
    at coretests::atomic::atomic_access_bool (coretests-3d2262867062fa53.wasm[25901]:0xffffffff)
    at coretests::atomic::atomic_access_bool::{{closure}} (coretests-3d2262867062fa53.wasm[25900]:0xffffffff)
    at core::ops::function::FnOnce::call_once (coretests-3d2262867062fa53.wasm[7577]:0xffffffff)
    at test::__rust_begin_short_backtrace (coretests-3d2262867062fa53.wasm[27649]:0xffffffff)
    at test::types::RunnableTest::run (coretests-3d2262867062fa53.wasm[27680]:0xffffffff)
    at test::run_test (coretests-3d2262867062fa53.wasm[27644]:0xffffffff)
    at test::run_tests (coretests-3d2262867062fa53.wasm[27642]:0xffffffff)
    at test::console::run_tests_console (coretests-3d2262867062fa53.wasm[27478]:0xffffffff)
    at test::test_main (coretests-3d2262867062fa53.wasm[27634]:0xffffffff)
    at test::test_main_static (coretests-3d2262867062fa53.wasm[27635]:0xffffffff)
    at coretests::main (coretests-3d2262867062fa53.wasm[12082]:0xffffffff)
    at core::ops::function::FnOnce::call_once (coretests-3d2262867062fa53.wasm[8940]:0xffffffff)
    at std::sys::backtrace::__rust_begin_short_backtrace (coretests-3d2262867062fa53.wasm[15611]:0xffffffff)
    at std::rt::lang_start::{{closure}} (coretests-3d2262867062fa53.wasm[675]:0xffffffff)
    at std::rt::lang_start_internal (coretests-3d2262867062fa53.wasm[27950]:0xffffffff)
    at std::rt::lang_start (coretests-3d2262867062fa53.wasm[674]:0xffffffff)
    at __main_void (coretests-3d2262867062fa53.wasm[12083]:0xffffffff)
    at _start (coretests-3d2262867062fa53.wasm[136]:0xffffffff)

More changed tests

• Python: tests_python_results.json
• Node.js: tests_node_results.json
• PHP: tests_php_results.json
• Rust: tests_rust_results.json

Install shield

• git clone https://github.com/wasmerio/compat-tests.git
• cd compat-tests
• cargo build
• ./target/debug/shield run --lang <LANG> --wasmer [WASMER BINARY] <TEST OR BATCH>

Artifacts

• GitHub Action: https://github.com/wasmerio/anti-regression-shield/actions/runs/25216344111
• Results commit: wasmerio/anti-regression-shield@30d19a5