On Thu, Oct 17, 2024 at 10:05:50PM GMT, Lorenzo Stoakes wrote:
> It is useful to be able to utilise the pidfd mechanism to reference the
> current thread or process (from a userland point of view - thread group
> leader from the kernel's point of view).
>
> Therefore introduce PIDFD_SELF_THREAD to refer to the current thread, and
> PIDFD_SELF_THREAD_GROUP to refer to the current thread group leader.
>
> For convenience and to avoid confusion from userland's perspective we alias
> these:
>
> * PIDFD_SELF is an alias for PIDFD_SELF_THREAD - This is nearly always what
> the user will want to use, as they would find it surprising if for
> instance fd's were unshared()'d and they wanted to invoke pidfd_getfd()
> and that failed.
>
> * PIDFD_SELF_PROCESS is an alias for PIDFD_SELF_THREAD_GROUP - Most users
> have no concept of thread groups or what a thread group leader is, and
> from userland's perspective and nomenclature this is what userland
> considers to be a process.
Should users use PIDFD_SELF_PROCESS in process_madvise() for self
madvise() (once the support is added)?
>
[...]
>
> +static struct pid *pidfd_get_pid_self(unsigned int pidfd, unsigned int *flags)
> +{
> + bool is_thread = pidfd == PIDFD_SELF_THREAD;
> + enum pid_type type = is_thread ? PIDTYPE_PID : PIDTYPE_TGID;
> + struct pid *pid = *task_pid_ptr(current, type);
> +
> + /* The caller expects an elevated reference count. */
> + get_pid(pid);
Do you want this helper to work for scenarios where pid is used across
context? Otherwise can't we get rid of this get and later put for self?
> + return pid;
> +}
> +
Overall looks good to me.
Reviewed-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
