Claude review: drm/etnaviv: use kzalloc_flex

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

Patch Review

**Correctness: OK**

The conversion is semantically correct:

- The old code computed the size manually via `size_vstruct(nr_bos, sizeof(submit->bos[0]), sizeof(*submit))` and passed it to `kzalloc(sz, GFP_KERNEL)`.
- The new code `kzalloc_flex(*submit, bos, nr_bos)` expands (via `__alloc_flex`) to use `struct_size_t()` for the same computation, and `default_gfp()` with no extra args defaults to `GFP_KERNEL` — matching the original behavior.
- `bos` is indeed the trailing flexible array member of `struct etnaviv_gem_submit` (declared as `struct etnaviv_gem_submit_bo bos[];` at `etnaviv_gem.h:108`).
- The removed `size_vstruct()` has no other callers in the etnaviv driver after this change, so its removal is safe.

**Overflow handling difference (minor):** The old `size_vstruct()` returned 0 on overflow, which would cause `kzalloc(0, GFP_KERNEL)` to return `ZERO_SIZE_PTR` — a non-NULL pointer that faults on dereference (a latent bug, though practically unreachable). The new `kzalloc_flex` uses `struct_size_t()` which returns `SIZE_MAX` on overflow, causing `kzalloc` to return NULL — which is actually the safer and correct behavior. So this is a minor improvement.

**Additional benefit:** `__alloc_flex` also calls `__set_flex_counter()` which, if the `bos` member is annotated with `__counted_by()`, will automatically set the counter field. This is a nice bonus for future hardening.

**Nit:** The commit message says "A local helper was developed previously for struct_size" — this is slightly inaccurate; the helper (`size_vstruct`) predates `struct_size` and is a hand-rolled size calculation, not built on `struct_size`. The message could be clearer, but it's not a blocking issue.

**Reviewed-by worthy: Yes.** The patch is a clean, correct conversion to the preferred kernel API.

---
Generated by Claude Code Patch Reviewer