In our MegaRAID driver, one of the IOCTLs is defined as #define MEGASAS_IOC_GET_AEN _IOW('M', 2, struct megasas_aen) This clashes with some other value in "built_in" ioctl table on x86_64 kernels. How do I really avoid such problems in the future. Even if I search the length of the built_in table and pick a unique value, is it guaranteed to be unique in the future releases? The Documentation/ioctl-number.txt isn't of much help either. It lists multiple conflicts. Moreover, not all of them are listed there. On a broader note, if the struct ioctl_trans inside ioctl32_hash_table could use the combination of cmd + major number instead of just cmd to determine the uniqueness, these conflicts could be avoided, right? I mean understand the reasons for system-wide unique ioctl numbers. But right now, only those platforms that need conversion are technically impeded for violating that guideline. Thanks, Sreenivas - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html