Claude review: rust: drm: gem: shmem: Add vmap functions

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Verdict: Looks good, minor nits.**

This is the largest patch and is well-structured. The `make_vmap()` pattern with generics to support both borrowed and owned references is clean.

**Size validation is correct:**
```rust
if self.size() < SIZE {
    return Err(ENOSPC);
}
```

**The iomem fallback returns `ENOTSUPP`:**
```rust
if map.is_iomem {
    unsafe { self.raw_vunmap(map) };
    Err(ENOTSUPP)
}
```
This is fine. `ENOTSUPP` vs `EOPNOTSUPP` has been debated in kernel circles, but both are used for this kind of situation. The cleanup path (calling `raw_vunmap` on the iomem map) is correct.

**VMap::drop reconstructs the iosys_map:**
```rust
fn drop(&mut self) {
    unsafe {
        self.owner.raw_vunmap(bindings::iosys_map {
            is_iomem: false,
            __bindgen_anon_1: bindings::iosys_map__bindgen_ty_1 { vaddr: self.addr },
        })
    };
}
```
This is correct since we only create VMap for non-iomem mappings (iomem returns an error in `make_vmap`).

**IoCapable implementations look correct.** The `ptr::read`/`ptr::write` calls delegate safety to the `Io` trait's bounds checking.

**Unit tests are good** -- they test compile-time size validation and basic I/O through the vmap. The kunit boilerplate DRM driver is minimal and appropriate.

**Nit:** In the `vmap_io` test, the read-back of individual bytes from a u32 write assumes little-endian. This will work on x86 and ARM (LE mode) but would be worth a comment or `#[cfg(target_endian = "little")]` if it matters for test correctness on BE platforms.

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Generated by Claude Code Patch Reviewer