On Thu, Jan 30, 2025 at 08:40:26PM +0000, 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.
We adjust pidfd_get_task() and the pidfd_send_signal() system call with specific handling for this, implementing this functionality for process_madvise(), process_mrelease() (albeit, using it here wouldn't really make sense) and pidfd_send_signal().
Signed-off-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
Reviewed-by: Shakeel Butt shakeel.butt@linux.dev