Path symlink follow (#1284)

* Fix the tests for correctly following symlinks.

* Correctly follow symlinks in path_link.

crates/test-programs/wasi-tests/src/bin/path_link.rs

@@ -152,26 +152,19 @@ unsafe fn test_path_link(dir_fd: wasi::Fd) {
     // Create a link to a dangling symlink
     wasi::path_symlink("target", dir_fd, "symlink").expect("creating a dangling symlink");
 
-    assert_eq!(
-        wasi::path_link(dir_fd, 0, "symlink", dir_fd, "link")
-            .expect_err("creating a link to a dangling symlink should fail")
-            .raw_error(),
-        wasi::ERRNO_NOENT,
-        "errno should be ERRNO_NOENT"
-    );
+    // This should succeed, because we're not following symlinks
+    wasi::path_link(dir_fd, 0, "symlink", dir_fd, "link")
+        .expect("creating a link to a dangling symlink should succeed");
     wasi::path_unlink_file(dir_fd, "symlink").expect("removing a symlink");
+    wasi::path_unlink_file(dir_fd, "link").expect("removing a hardlink");
 
     // Create a link to a symlink loop
     wasi::path_symlink("symlink", dir_fd, "symlink").expect("creating a symlink loop");
 
-    assert_eq!(
-        wasi::path_link(dir_fd, 0, "symlink", dir_fd, "link")
-            .expect_err("creating a link to a symlink loop")
-            .raw_error(),
-        wasi::ERRNO_LOOP,
-        "errno should be ERRNO_LOOP"
-    );
+    wasi::path_link(dir_fd, 0, "symlink", dir_fd, "link")
+        .expect("creating a link to a symlink loop should succeed");
     wasi::path_unlink_file(dir_fd, "symlink").expect("removing a symlink");
+    wasi::path_unlink_file(dir_fd, "link").expect("removing a hardlink");
 
     // Create a link where target is a dangling symlink
     wasi::path_symlink("target", dir_fd, "symlink").expect("creating a dangling symlink");
@@ -203,6 +196,7 @@ unsafe fn test_path_link(dir_fd: wasi::Fd) {
     // Create a link where target is a dangling symlink following symlinks
     wasi::path_symlink("target", dir_fd, "symlink").expect("creating a dangling symlink");
 
+    // If we do follow symlinks, this should fail
     assert_eq!(
         wasi::path_link(
             dir_fd,
@@ -211,7 +205,7 @@ unsafe fn test_path_link(dir_fd: wasi::Fd) {
             dir_fd,
             "link",
         )
-        .expect_err("creating a link where target is a dangling symlink following symlinks")
+        .expect_err("creating a link to a dangling symlink following symlinks should fail")
         .raw_error(),
         wasi::ERRNO_NOENT,
         "errno should be ERRNO_NOENT"

crates/wasi-common/src/hostcalls_impl/fs.rs

@@ -650,7 +650,9 @@ pub(crate) unsafe fn path_link(
         false,
     )?;
 
-    hostcalls_impl::path_link(resolved_old, resolved_new)
+    let follow_symlinks = old_flags & wasi::__WASI_LOOKUPFLAGS_SYMLINK_FOLLOW != 0;
+
+    hostcalls_impl::path_link(resolved_old, resolved_new, follow_symlinks)
 }
 
 pub(crate) unsafe fn path_open(

crates/wasi-common/src/sys/unix/hostcalls_impl/fs.rs

@@ -71,15 +71,24 @@ pub(crate) fn path_create_directory(base: &File, path: &str) -> WasiResult<()> {
     unsafe { mkdirat(base.as_raw_fd(), path, Mode::from_bits_truncate(0o777)) }.map_err(Into::into)
 }
 
-pub(crate) fn path_link(resolved_old: PathGet, resolved_new: PathGet) -> WasiResult<()> {
+pub(crate) fn path_link(
+    resolved_old: PathGet,
+    resolved_new: PathGet,
+    follow_symlinks: bool,
+) -> WasiResult<()> {
     use yanix::file::{linkat, AtFlag};
+    let flags = if follow_symlinks {
+        AtFlag::SYMLINK_FOLLOW
+    } else {
+        AtFlag::empty()
+    };
     unsafe {
         linkat(
             resolved_old.dirfd().as_raw_fd(),
             resolved_old.path(),
             resolved_new.dirfd().as_raw_fd(),
             resolved_new.path(),
-            AtFlag::SYMLINK_FOLLOW,
+            flags,
         )
     }
     .map_err(Into::into)

crates/wasi-common/src/sys/windows/hostcalls_impl/fs.rs

@@ -129,7 +129,11 @@ pub(crate) fn path_create_directory(file: &File, path: &str) -> WasiResult<()> {
     std::fs::create_dir(&path).map_err(Into::into)
 }
 
-pub(crate) fn path_link(resolved_old: PathGet, resolved_new: PathGet) -> WasiResult<()> {
+pub(crate) fn path_link(
+    resolved_old: PathGet,
+    resolved_new: PathGet,
+    follow_symlinks: bool,
+) -> WasiResult<()> {
     unimplemented!("path_link")
 }