On Thu, May 21, 2026 at 11:57:09PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <[email protected]>
>
> Add get_boot_id() to expose current boot ID to other kernel subsystems.
> Note that since this is only meaningful if user can access it via sysctl,
> it returns NULL if CONFIG_SYSCTL=n.
Wouldn't this be nice to have even on !SYSCTL systems? Why disable it for this
case?
> +/**
> + * get_boot_id - return the boot ID UUID
> + *
> + * This function returns a pointer to the boot ID UUID, which is generated on
> + * demand the first time this function is called. The boot ID is a UUID that
> + * is unique to each boot of the system.
> + */
> +const u8 *get_boot_id(void)
> +{
> + static DEFINE_SPINLOCK(bootid_spinlock);
> +
> + spin_lock(&bootid_spinlock);
> + if (!sysctl_bootid[8])
> + generate_random_uuid(sysctl_bootid);
> + spin_unlock(&bootid_spinlock);
> +
> + return sysctl_bootid;
> +}
> +
> /*
> * This function is used to return both the bootid UUID, and random
> * UUID. The difference is in whether table->data is NULL; if it is,
> @@ -1638,12 +1657,8 @@ static int proc_do_uuid(const struct ctl_table *table,
> int write, void *buf,
> uuid = tmp_uuid;
> generate_random_uuid(uuid);
> } else {
> - static DEFINE_SPINLOCK(bootid_spinlock);
> -
> - spin_lock(&bootid_spinlock);
> - if (!uuid[8])
> - generate_random_uuid(uuid);
> - spin_unlock(&bootid_spinlock);
> + /* Ensure that the boot ID is initialized. */
> + get_boot_id();
I find this a little odd, this implicit behavior now that sysctl_bootid ==
uuid. But perhaps that's the cleanest approach there is?
