[CRIU] [PATCH] restorer: rework unmaping old VMA-s

[Pavel Emelyanov]

> @@ -523,6 +523,37 @@ void __export_unmap(void)
>  }
>  
>  /*
> + * This function unmaps all VMAs, which don't belong to
> + * the restored process or the restorer
> + */
> +static int unmap_old_vmas(void *premmapped_addr, unsigned long premmapped_len,
> +		      void *bootstrap_start, unsigned long bootstrap_len)
> +{
> +	void *p[6] = {NULL, 0, 0, 0, 0, (void *) TASK_SIZE};
> +	int xchg, i;
> +
> +	/* Sorting vma-s */
> +	xchg = premmapped_addr > bootstrap_start ? 2 : 0;
> +
> +	p[1 + xchg] = premmapped_addr;
> +	p[2 + xchg] = premmapped_addr + premmapped_len;
> +	p[3 - xchg] = bootstrap_start;
> +	p[4 - xchg] = bootstrap_start + bootstrap_len;
> +
> +	for (i = 0; i < 6; i += 2) {
> +		int ret;
> +		ret = sys_munmap(p[i], p[i + 1] - p[i]);
> +		if (ret) {
> +			pr_err("Unable to unmap (%p-%p): %d\n",
> +						p[i], p[i + 1], ret);
> +			return -1;
> +		}
> +	}
> +
> +	return 0;

This is very hard to read. Why not make it simpler?

if (premmapped_addr < bootstrap_addr) {
	area_1_start = premmaped_addr;
	area_1_end = premmaped_addr + premmapped_len;
	area_2_start = bootstrap_start;
	area_2_end = bootstrap_start + bootstrap_len;
} else {
	area_1_start = bootstrap_start;
	area_1_end = bootstrap_start + bootstrap_len;
	area_2_start = premmaped_addr;
	area_2_end = premmaped_addr + premmapped_len;
}

sys_munmap(0,          area_1_start);
sys_munmap(area_1_end, area_2_start - area_1_end);
sys_munmap(area_2_end, TASK_SIZE - area_2_end);

> +}
> +
> +/*
>   * The main routine to restore task via sigreturn.
>   * This one is very special, we never return there
>   * but use sigreturn facility to restore core registers