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([2401:4900:b4fc:c14c:ba99:ba0e:908b:8404]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b04f40f515sm34153085ad.74.2026.03.15.14.47.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Mar 2026 14:47:26 -0700 (PDT) From: Mathura_Kumar To: brauner@kernel.org Cc: academic1mathura@gmail.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk Subject: [PATCH v2 0/4] Add new system call for non-destructive peek and inspection to posix ipc mqueue Date: Mon, 16 Mar 2026 03:16:50 +0530 Message-ID: <20260315214656.658590-1-academic1mathura@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Patch series overview: 1. Add New system call do_mq_timedreceive2() and handler implementation 2. Add system call number in all most common arch. 3. Prepared Documentation and test 4. Add entry in performance tools all most common file Short Description: POSIX message queues currently lack a mechanism to read a message without removing it from the queue. This is a long-standing limitation,when we require inspection of queue state without altering it. Design considerations: Two approaches for copying message data to userspace were evaluated: 1) Refcount-based message lifecycle handling - This can help us Avoids intermediate temp kernel copy - Extends message lifetime -But this may increase writer starvation under heavy load and add unnecessary complication on priority management and delay more time to free space in inode due refcount may prevent 2) Temporary kernel buffer copy - Copies message into a bounded kernel buffer - Reduces time message remains locked - Improves fairness under write-heavy workloads - Simpler lifetime management My implementation adopts the temporary buffer approach to minimize starvation and reduce locking complexity. The design allows future transition if refcounting is deemed preferable. Testing: - 17 functional test cases - Multi-threaded producer/consumer scenarios - concurrent pop and peek - Edge cases: empty queue, FIFO invalid flags, signal interruption etc. Use Case: 1) Observability in distributed systems e.g Monitoring tools can inspect queue contents without interfering with normal processing 2) Check pointing system like CRIU can have a look into queue without consuming and can store messages 3) Resource-aware processing 4) Selective Consumption for Specialized Workers change since v1: - minor update, header guard was removed from include/uapi/linux/mqueue.h - v1 Link: https://lore.kernel.org/all/20260315040827.156558-1-academic1mathura@gmail.com/T/#t Thanks for reviewing. Documentation/userspace-api/index.rst | 1 + Documentation/userspace-api/ipc.rst | 222 +++++ arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/tools/syscall_32.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + include/linux/compat.h | 6 +- include/linux/syscalls.h | 6 + include/uapi/asm-generic/unistd.h | 7 +- include/uapi/linux/mqueue.h | 14 +- ipc/mqueue.c | 186 ++++- ipc/msg.c | 2 +- ipc/msgutil.c | 48 +- ipc/util.h | 3 +- kernel/sys_ni.c | 1 + scripts/syscall.tbl | 1 + .../arch/alpha/entry/syscalls/syscall.tbl | 1 + .../perf/arch/arm/entry/syscalls/syscall.tbl | 1 + .../arch/arm64/entry/syscalls/syscall_32.tbl | 1 + .../arch/mips/entry/syscalls/syscall_n64.tbl | 1 + .../arch/parisc/entry/syscalls/syscall.tbl | 1 + .../arch/powerpc/entry/syscalls/syscall.tbl | 1 + .../perf/arch/s390/entry/syscalls/syscall.tbl | 1 + tools/perf/arch/sh/entry/syscalls/syscall.tbl | 1 + .../arch/sparc/entry/syscalls/syscall.tbl | 1 + .../arch/x86/entry/syscalls/syscall_32.tbl | 1 + .../arch/x86/entry/syscalls/syscall_64.tbl | 1 + .../arch/xtensa/entry/syscalls/syscall.tbl | 1 + tools/scripts/syscall.tbl | 1 + tools/testing/selftests/ipc/.gitignore | 1 + tools/testing/selftests/ipc/Makefile | 9 +- tools/testing/selftests/ipc/mq_peek.c | 785 ++++++++++++++++++ 44 files changed, 1278 insertions(+), 43 deletions(-) create mode 100644 Documentation/userspace-api/ipc.rst create mode 100644 tools/testing/selftests/ipc/mq_peek.c -- 2.43.0