Claude review: User readable error codes on atomic_ioctl failure

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

Overall Series Review

Subject: User readable error codes on atomic_ioctl failure
Author: Arun R Murthy <arun.r.murthy@intel.com>
Patches: 8
Reviewed: 2026-04-01T07:55:26.976758

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This v11 series adds user-readable error codes to `drm_atomic_ioctl()` by repurposing the `reserved` field in `struct drm_mode_atomic` as a pointer to a userspace `struct drm_mode_atomic_err_code`. The concept has value -- compositors currently get bare `-EINVAL` and must guess what went wrong. However, the implementation has **significant UAPI design issues, multiple bugs, typos in the ABI, and a memory leak** that need addressing before this can be merged.

**Key concerns:**
1. **Breaking the `reserved` field contract** -- The `reserved` field was previously validated to be zero, ensuring old kernels reject new userspace and vice versa. This patch silently removes that check, meaning old userspace that accidentally has garbage in `reserved` will now trigger `copy_to_user` to a random address instead of getting `-EINVAL`.
2. **Memory leak** in `drm_mode_atomic_add_error_msg()` -- `kvasprintf()` allocates memory that is never freed.
3. **Typos baked into UAPI** -- `DRM_MODE_ATTOMIC_*`, `VIOLOATION`, `invallid`, `falg` -- these become permanent ABI once merged.
4. **`error_code_ptr` used uninitialized** when `arg->reserved == 0` and an error occurs on a code path that was present before patch 4 moved allocation earlier.

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