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From: Shakeel Butt To: Lorenzo Stoakes Cc: Christian Brauner , Shuah Khan , "Liam R . Howlett" , Suren Baghdasaryan , Vlastimil Babka , pedro.falcato@gmail.com, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Oliver Sang , John Hubbard , Tejun Heo , Johannes Weiner , Michal Koutny , Andrew Morton Subject: Re: [PATCH v7 1/6] pidfd: add PIDFD_SELF* sentinels to refer to own thread/process Message-ID: References: <24315a16a3d01a548dd45c7515f7d51c767e954e.1738268370.git.lorenzo.stoakes@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <24315a16a3d01a548dd45c7515f7d51c767e954e.1738268370.git.lorenzo.stoakes@oracle.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C849C160006 X-Stat-Signature: mkoazz4o7uiqcxrajwrad1547pg45p7t X-Rspam-User: X-HE-Tag: 1738687876-140331 X-HE-Meta: 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 veauAmhV X5fsore6DvF7vB9afGQgWDloVcRwDK5b00ytku+HVSqqYFbxgIiIBB7EDpyaRFr2XNyvl4+2bcQKEJpXCogP4+fPu5Ygy75qibTr6+Pqz2Ed5Iwg0wKV+JDmF1aHe6DZS8HH/WWq9CFz5BdPoLj59915+xN70HFxqovwMhTOXY7fB5SE0YjitME/2NM2ptbkEAkIRtshNJMS+Qd5MFRpHhMyOcYe4ROlQdigj89HstEZJZ5Pp7IBhn8kppDblNhIW3XDdovtJe5fEjvtXBRaQ56Pu3sm5CaR9U3+3koKkMoRRSvFiTBsgxmxeW2OiB2gIyvVZ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Reviewed-by: Shakeel Butt