[PATCH] mqueue: introduce new do_mq_timedreceive2() [ mq_peek syscall] for non-destructive receive and inspection,fix minor issue,prepared doc.
From: Mathura_Kumar
Date: Thu Mar 05 2026 - 13:11:12 EST
First of all Thanks for constructive response,I am new to kernel development
so in earlier patch has some style issue
what changed now:-
1)As per my estimate all style issue fixed
2)Doc was prepared in Documentation/userspace-api/syscall.rst, for better
consistency, i was not making inline comment for doc in source code
3)I am squashing previous three commit in this latest one for convenience in applying
and merging
Required Attention:-As per mail from bot
kernel test robot noticed the following build errors:
[auto build test ERROR on shuah-kselftest/next]
[also build test ERROR on shuah-kselftest/fixes next-20260304]
[cannot apply to arnd-asm-generic/master linus/master tip/x86/asm v6.16-rc1]
As per my guess bot failed to apply all earlier patch in order,now As Squashed,
it should not come but if it then required manual intervention, I tested Successfully
on x86-64 bit host arch for x86-64,arm64,risc-v and all test.
some note:-macro and header guard are extermally sensetive for order of sys call number
on risc-v ,after of hour testing ,hit and trail and i fix that
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.
Modifying existing mq_receive() semantics via additional
flags was considered. However, altering behavior of an
existing syscall risks breaking backward compatibility
for applications relying on current semantics. Since
mq_receive() guarantees message removal, changing this
contract is not safe.
To preserve ABI stability, this patch introduces a new
system call that performs a non-destructive receive
operation (peek). The existing behavior remains unchanged.
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 unneassery 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.
Architecture support: ALL
Testing:
- 15+ functional test cases
- Multi-threaded producer/consumer scenarios
- concurrent pop and peek
- Edge cases: empty queue, FIFO
invalid flags, signal interruption etc.
Signed-off-by: Mathura_Kumar <academic1mathura@xxxxxxxxx>
---
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/syscall.rst | 273 +++++++
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 2 +
arch/arm64/tools/syscall_32.tbl | 2 +
arch/m68k/kernel/syscalls/syscall.tbl | 3 +
arch/microblaze/kernel/syscalls/syscall.tbl | 3 +
arch/mips/kernel/syscalls/syscall_n32.tbl | 2 +
arch/mips/kernel/syscalls/syscall_n64.tbl | 1 +
arch/mips/kernel/syscalls/syscall_o32.tbl | 2 +
arch/powerpc/kernel/syscalls/syscall.tbl | 3 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 2 +
arch/sparc/kernel/syscalls/syscall.tbl | 3 +
arch/x86/entry/syscalls/syscall_32.tbl | 2 +
arch/x86/entry/syscalls/syscall_64.tbl | 2 +
arch/xtensa/kernel/syscalls/syscall.tbl | 2 +
include/linux/syscalls.h | 10 +
include/uapi/asm-generic/unistd.h | 12 +-
ipc/mqueue.c | 183 +++++
ipc/msg.c | 2 +-
ipc/msgutil.c | 49 +-
ipc/util.h | 3 +-
kernel/sys_ni.c | 2 +
scripts/checksyscalls.sh | 1 +
scripts/syscall.tbl | 3 +
tools/testing/selftests/ipc/.gitignore | 1 +
tools/testing/selftests/ipc/Makefile | 5 +-
tools/testing/selftests/ipc/mq_peek.c | 794 ++++++++++++++++++++
29 files changed, 1337 insertions(+), 33 deletions(-)
create mode 100644 Documentation/userspace-api/syscall.rst
create mode 100644 tools/testing/selftests/ipc/mq_peek.c
diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index a68b1bea57a8..119f820a5a1d 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -22,6 +22,7 @@ System calls
ioctl/index
mseal
rseq
+ syscall
Security-related interfaces
===========================
diff --git a/Documentation/userspace-api/syscall.rst b/Documentation/userspace-api/syscall.rst
new file mode 100644
index 000000000000..236c4cb88544
--- /dev/null
+++ b/Documentation/userspace-api/syscall.rst
@@ -0,0 +1,273 @@
+mq_timedreceive2 system call
+=============================
+
+This document describes the mq_timedreceive2() system call. It provides
+an overview of the feature, its motivation, interface specification,
+design, and test specification.
+
+Contents
+--------
+
+ 1) Overview
+ 2) Motivation
+ 3) Functional Specification
+ 4) Design
+ 5) Implementation Notes
+ 6) Test Specification
+
+1) Overview
+-----------
+
+POSIX message queues on Linux provide mq_receive() and mq_timedreceive()
+for consuming messages from a queue. Both interfaces require the caller
+to pass the message buffer, length, and priority pointer as individual
+arguments to the system call. This imposes a fixed calling convention
+that cannot be extended without breaking the ABI.
+
+mq_timedreceive2() introduces a new system call entry point that accepts
+message buffer parameters via a struct argument rather than as individual
+syscall arguments. This frees the remaining syscall argument slots for
+new functionality flags and a message index, enabling non-destructive
+peek and indexed access semantics that are not possible with the
+original interface.
+
+Two variants are provided:
+
+ mq_timedreceive2() - primary variant, 64-bit time (Y2038-safe)
+ mq_timedreceive2_time32() - 32-bit time variant for legacy and compat
+
+2) Motivation
+-------------
+
+The original mq_timedreceive() interface exhausts all usable syscall
+argument slots with mqdes, msg_ptr, msg_len, msg_prio, and abs_timeout.
+Adding new behavior such as peek-without-consume or indexed message
+access would require either a new syscall with a completely different
+signature, or overloading existing arguments in ways that harm clarity
+and correctness.
+
+By consolidating the message buffer parameters into a struct, this
+syscall recovers argument slots for:
+
+ flags - controls peek vs consume and other future behavior
+ index - selects a specific message position in the priority queue
+
+This design follows the precedent of other Linux syscalls that use
+struct arguments to allow forward-compatible extensibility, such as
+clone3() and openat2().
+
+2.1 Non-destructive peek
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+When the appropriate flag is set, mq_timedreceive2() copies the
+message into the caller's buffer without removing it from the queue.
+The queue state and priority ordering are fully preserved. This allows
+applications to inspect a message before deciding whether to consume
+it, eliminating the need to re-queue messages and the race conditions
+that re-queuing introduces in multi-consumer scenarios.
+
+2.2 Indexed access
+~~~~~~~~~~~~~~~~~~
+
+The index argument allows the caller to address a specific position
+within the priority-ordered queue rather than always receiving the
+highest priority message. This is useful for queue inspection,
+debugging, and monitoring tools that need visibility into queue
+contents without disturbing normal consumers.
+
+3) Functional Specification
+---------------------------
+
+NAME
+ mq_timedreceive2 - receive or peek at a message from a
+ POSIX message queue
+
+SYNOPSIS
+
+.. code-block:: c
+
+ #include <mqueue.h>
+
+ struct mq_timedreceive2_args {
+ size_t msg_len;
+ unsigned int *msg_prio;
+ char *msg_ptr;
+ };
+
+ ssize_t mq_timedreceive2(mqd_t mqdes,
+ struct mq_timedreceive2_args *uargs,
+ unsigned int flags,
+ unsigned long index,
+ const struct timespec *abs_timeout);
+
+Note: No glibc wrapper exists for this syscall. Callers must invoke it
+directly using syscall(2).
+
+DESCRIPTION
+ mq_timedreceive2() receives or peeks at a message from the
+ message queue referred to by the descriptor mqdes.
+
+ The uargs structure provides the message buffer parameters:
+
+ ``msg_ptr``
+ Userspace buffer to receive the message body.
+
+ ``msg_len``
+ Size of msg_ptr in bytes. Must be greater than or equal
+ to the mq_msgsize attribute of the queue.
+
+ ``msg_prio``
+ If not NULL, the priority of the received message is
+ stored here.
+
+ The flags argument controls receive behavior. The following
+ flag is defined:
+
+ ``MQ_PEEK``
+ Copy the message into msg_ptr without removing it from
+ the queue. The queue is not modified. If this flag is
+ not set, behavior is identical to mq_timedreceive() and
+ the message is consumed.
+
+ The index argument selects which message to operate on within
+ the priority-ordered queue. index 0 refers to the highest
+ priority message. When MQ_PEEK is not set, index is ignored
+ but must be 0.
+
+ The abs_timeout argument specifies an absolute timeout. When
+ MQ_PEEK is set, abs_timeout is ignored since peek is a
+ non-blocking snapshot operation. When MQ_PEEK is not set,
+ abs_timeout behaves identically to mq_timedreceive().
+
+RETURN VALUE
+ On success, returns the number of bytes copied into msg_ptr.
+ On failure, returns -1 and sets errno.
+
+ERRORS
+ ``EAGAIN``
+ Queue is empty and MQ_PEEK is set. Peek is always
+ non-blocking and returns immediately on empty queue.
+
+ ``EBADF``
+ mqdes is not a valid message queue descriptor open
+ for reading.
+
+ ``EFAULT``
+ uargs, msg_ptr, msg_prio, or abs_timeout points to
+ an invalid address.
+
+ ``EINVAL``
+ flags contains an unknown value, or index is nonzero
+ and MQ_PEEK is not set.
+
+ ``EMSGSIZE``
+ msg_len is less than the mq_msgsize attribute of
+ the queue.
+
+ ``ETIMEDOUT``
+ Pop path only. The call timed out before a message
+ became available. Never returned on peek path.
+
+4) Design
+---------
+
+4.1 Struct-based argument passing
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The message buffer parameters (msg_ptr, msg_len, msg_prio) are
+consolidated into struct mq_timedreceive2_args rather than passed
+as individual syscall arguments. Linux syscalls are limited to six
+arguments. The original mq_timedreceive() consumes all six slots,
+leaving no room for extension. Consolidating the buffer parameters
+into a struct recovers two argument slots for flags and index while
+keeping the interface clean and forward-compatible.
+
+Future extensions can be made by adding new flag bits without
+requiring a new syscall number, following the same extensibility
+model as openat2() and clone3().
+
+4.2 Compat handling
+~~~~~~~~~~~~~~~~~~~~
+
+32-bit userspace on 64-bit kernels requires a separate compat
+variant because pointer sizes and alignment differ between ABIs.
+mq_timedreceive2_time32() accepts struct compat_mq_timedreceive2_args
+which uses compat_uptr_t and compat_size_t in place of native pointer
+and size_t types, and struct old_timespec32 for the timeout.
+
+.. code-block:: c
+
+ struct compat_mq_timedreceive2_args {
+ compat_size_t msg_len;
+ compat_uptr_t msg_prio;
+ compat_uptr_t msg_ptr;
+ };
+
+The compat entry point performs the necessary conversions before
+calling the shared do_mq_timedreceive2() implementation.
+
+4.3 Peek implementation
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+When MQ_PEEK is set, the implementation locates the target message
+in the priority tree but does not remove it. Two locks are taken:
+the first confirms a message exists before any allocation is
+attempted, avoiding allocation on empty queues. The second protects
+the kernel temporary buffer copy operation. The message is copied to
+userspace and both locks are released with the queue unmodified.
+
+4.4 Index argument
+~~~~~~~~~~~~~~~~~~~
+
+The priority tree is walked to the node at position index within
+the priority ordering. index 0 is always the highest priority
+message, consistent with what an unconditional mq_timedreceive()
+would return.
+
+5) Implementation Notes
+-----------------------
+
+The implementation lives in ipc/mqueue.c. The two syscall entry
+points mq_timedreceive2 and mq_timedreceive2_time32 are thin wrappers
+that validate and convert arguments before calling the shared internal
+function do_mq_timedreceive2(). This mirrors the existing pattern used
+by mq_timedreceive and mq_timedreceive_time32.
+
+Syscall numbers are assigned for all supported architectures. Refer
+to the respective syscall table files under arch/ for per-architecture
+numbers.
+
+6) Test Specification
+---------------------
+
+Tests for mq_timedreceive2() should cover the following:
+
+1) Basic receive: verify that without MQ_PEEK the message is consumed
+ and queue depth decreases by one. Verify message body and priority
+ are correct.
+
+2) Peek semantics: verify that with MQ_PEEK the message body and
+ priority are returned correctly and the queue depth is unchanged
+ after the call.
+
+3) Repeated peek: verify that calling mq_timedreceive2() with MQ_PEEK
+ multiple times on the same queue returns the same message each time
+ without modifying the queue.
+
+4) Index argument: verify that index 0 returns the highest priority
+ message. Verify that out-of-range index returns ENOENT.
+
+5) Empty queue: verify that peek on an empty queue returns EAGAIN
+ immediately without blocking.
+
+6) Memory behavior: verify that both small and large message copies
+ work correctly without corruption.
+
+7) Invalid arguments: verify EBADF for invalid mqdes, EFAULT for bad
+ pointers in uargs, EINVAL for unknown flags, EMSGSIZE for msg_len
+ smaller than queue mq_msgsize.
+
+8) Concurrent access: verify that simultaneous peek from multiple
+ threads returns consistent results and does not corrupt queue
+ state. Verify that a concurrent mq_receive() and mq_peek() do
+ not race or oops.
\ No newline at end of file
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index f31b7afffc34..0ff42d241419 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -511,3 +511,4 @@
579 common file_setattr sys_file_setattr
580 common listns sys_listns
581 common rseq_slice_yield sys_rseq_slice_yield
+582 common mq_timedreceive2 sys_mq_timedreceive2
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index 94351e22bfcf..bcec28be852c 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -486,3 +486,5 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 common mq_timedreceive2 sys_mq_timedreceive2_time32
+473 common mq_timedreceive2_time64 sys_mq_timedreceive2
diff --git a/arch/arm64/tools/syscall_32.tbl b/arch/arm64/tools/syscall_32.tbl
index 62d93d88e0fe..02603704231e 100644
--- a/arch/arm64/tools/syscall_32.tbl
+++ b/arch/arm64/tools/syscall_32.tbl
@@ -483,3 +483,5 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 common mq_timedreceive2_time64 sys_mq_timedreceive2
+473 common mq_timedreceive2 sys_mq_timedreceive2_time32
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 248934257101..b67f23edda11 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -471,3 +471,6 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 common mq_timedreceive2 sys_mq_timedreceive2_time32
+473 common mq_timedreceive2_time64 sys_mq_timedreceive2
+
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 223d26303627..89fb60006a99 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -477,3 +477,6 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 common mq_timedreceive2 sys_mq_timedreceive2_time32
+473 common mq_timedreceive2_time64 sys_mq_timedreceive2
+
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 7430714e2b8f..fee830be67a6 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -410,3 +410,5 @@
469 n32 file_setattr sys_file_setattr
470 n32 listns sys_listns
471 n32 rseq_slice_yield sys_rseq_slice_yield
+472 n32 mq_timedreceive2 sys_mq_timedreceive2_time32
+473 n32 mq_timedreceive2_time64 sys_mq_timedreceive2
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 630aab9e5425..75de6ee2df94 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -386,3 +386,4 @@
469 n64 file_setattr sys_file_setattr
470 n64 listns sys_listns
471 n64 rseq_slice_yield sys_rseq_slice_yield
+472 n64 mq_timedreceive2 sys_mq_timedreceive2
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 128653112284..8694a2d2f084 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -459,3 +459,5 @@
469 o32 file_setattr sys_file_setattr
470 o32 listns sys_listns
471 o32 rseq_slice_yield sys_rseq_slice_yield
+472 o32 mq_timedreceive2 sys_mq_timedreceive2_time32
+473 o32 mq_timedreceive2_time64 sys_mq_timedreceive2
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 4fcc7c58a105..fd90a2f500b6 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -562,3 +562,6 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 nospu rseq_slice_yield sys_rseq_slice_yield
+472 32 mq_timedreceive2 sys_mq_timedreceive2_time32
+473 64 mq_timedreceive2 sys_mq_timedreceive2
+474 32 mq_timedreceive2_time64 sys_mq_timedreceive2 sys_mq_timedreceive2
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 09a7ef04d979..34df682061d9 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -398,3 +398,4 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 common mq_timedreceive2 sys_mq_timedreceive2
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 70b315cbe710..1796ccd23d10 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -475,3 +475,5 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 common mq_timedreceive2 sys_mq_timedreceive2_time32
+473 common mq_timedreceive2_time64 sys_mq_timedreceive2
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 7e71bf7fcd14..5cfde6e0e6ba 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -517,3 +517,6 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 32 mq_timedreceive2 sys_mq_timedreceive2_time32
+473 64 mq_timedreceive2 sys_mq_timedreceive2
+474 32 mq_timedreceive2_time64 sys_mq_timedreceive2 sys_mq_timedreceive2
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index f832ebd2d79b..d6701f763203 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -477,3 +477,5 @@
469 i386 file_setattr sys_file_setattr
470 i386 listns sys_listns
471 i386 rseq_slice_yield sys_rseq_slice_yield
+472 i386 mq_timedreceive2 sys_mq_timedreceive2_time32
+473 i386 mq_timedreceive2_time64 sys_mq_timedreceive2
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 524155d655da..539654953280 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -441,3 +441,5 @@
547 x32 pwritev2 compat_sys_pwritev64v2
# This is the end of the legacy x32 range. Numbers 548 and above are
# not special and are not to be used for x32-specific syscalls.
+# Adding new syscalls from here to keep marginal gap intact in 472 to 511 for future expansion
+548 common mq_timedreceive2 sys_mq_timedreceive2
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index a9bca4e484de..9f69ef99e617 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -442,3 +442,5 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 common mq_timedreceive2 sys_mq_timedreceive2_time32
+473 common mq_timedreceive2_time64 sys_mq_timedreceive2
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 02bd6ddb6278..307cfd6f154c 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -93,6 +93,7 @@ struct file_attr;
#include <linux/key.h>
#include <linux/personality.h>
#include <trace/syscall.h>
+#include <linux/mqueue.h>
#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
/*
@@ -746,6 +747,15 @@ asmlinkage long sys_mq_timedsend_time32(mqd_t mqdes,
const char __user *u_msg_ptr,
unsigned int msg_len, unsigned int msg_prio,
const struct old_timespec32 __user *u_abs_timeout);
+asmlinkage long
+sys_mq_timedreceive2(mqd_t mqdes, struct mq_timedreceive2_args __user *uargs,
+ unsigned int flags, unsigned long index,
+ struct __kernel_timespec __user *abs_timeout);
+asmlinkage long
+sys_mq_timedreceive2_time32(mqd_t mqdes,
+ struct mq_timedreceive2_args __user *uargs,
+ unsigned int flags, unsigned long index,
+ struct old_timespec32 __user *abs_timeout);
asmlinkage long sys_msgget(key_t key, int msgflg);
asmlinkage long sys_old_msgctl(int msqid, int cmd, struct msqid_ds __user *buf);
asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index a627acc8fb5f..3e1c580a8b1f 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -863,9 +863,17 @@ __SYSCALL(__NR_listns, sys_listns)
#define __NR_rseq_slice_yield 471
__SYSCALL(__NR_rseq_slice_yield, sys_rseq_slice_yield)
-#undef __NR_syscalls
-#define __NR_syscalls 472
+#if defined(__SYSCALL_COMPAT) || __BITS_PER_LONG == 32
+#define __NR_mq_timedreceive2_time64 472
+__SYSCALL(__NR_mq_timedreceive2_time64, sys_mq_timedreceive2)
+#endif
+#if defined(__ARCH_WANT_TIME32_SYSCALLS) || __BITS_PER_LONG != 32
+#define __NR_mq_timedreceive2 473
+__SC_3264(__NR_mq_timedreceive2, sys_mq_timedreceive2_time32, sys_mq_timedreceive2)
+#endif
+#undef __NR_syscalls
+#define __NR_syscalls 474
/*
* 32 bit systems traditionally used different
* syscalls for off_t and loff_t arguments, while
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 4798b375972b..0278b60e8386 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -53,6 +53,7 @@ struct mqueue_fs_context {
#define SEND 0
#define RECV 1
+#define MQ_PEEK 2
#define STATE_NONE 0
#define STATE_READY 1
@@ -63,6 +64,12 @@ struct posix_msg_tree_node {
int priority;
};
+struct mq_timedreceive2_args {
+ size_t msg_len;
+ unsigned int *msg_prio;
+ char *msg_ptr;
+};
+
/*
* Locking:
*
@@ -1230,6 +1237,120 @@ static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
return ret;
}
+static struct msg_msg *mq_peek_index(struct mqueue_inode_info *info, int index)
+{
+ struct rb_node *node;
+ struct posix_msg_tree_node *leaf;
+ struct msg_msg *msg;
+
+ int count = 0;
+
+ /* Start from highest priority */
+ node = rb_last(&info->msg_tree);
+ while (node) {
+ leaf = rb_entry(node, struct posix_msg_tree_node, rb_node);
+ list_for_each_entry(msg, &leaf->msg_list, m_list) {
+ if (count == index)
+ return msg;
+ count++;
+ }
+
+ node = rb_prev(node);
+ }
+
+ return NULL;
+}
+
+static int do_mq_timedreceive2(mqd_t mqdes,
+ struct mq_timedreceive2_args __user *uargs,
+ unsigned int flags, unsigned long index,
+ struct timespec64 *ts)
+{
+ struct mq_timedreceive2_args args;
+ ssize_t ret;
+ struct msg_msg *msg_ptr, *k_msg_buffer;
+ long k_m_type;
+ size_t k_m_ts;
+ struct inode *inode;
+ struct mqueue_inode_info *info;
+
+ if (copy_from_user(&args, uargs, sizeof(args)))
+ return -EFAULT;
+
+ if (!(flags & MQ_PEEK)) {
+ return do_mq_timedreceive(mqdes, args.msg_ptr, args.msg_len,
+ args.msg_prio, ts);
+ }
+ audit_mq_sendrecv(mqdes, args.msg_len, 0, ts);
+ CLASS(fd, f)(mqdes);
+ if (fd_empty(f))
+ return -EBADF;
+
+ inode = file_inode(fd_file(f));
+ if (unlikely(fd_file(f)->f_op != &mqueue_file_operations))
+ return -EBADF;
+ info = MQUEUE_I(inode);
+ audit_file(fd_file(f));
+
+ if (unlikely(!(fd_file(f)->f_mode & FMODE_READ)))
+ return -EBADF;
+
+ if (unlikely(args.msg_len < info->attr.mq_msgsize))
+ return -EMSGSIZE;
+ if (index >= (unsigned long)info->attr.mq_maxmsg)
+ return -ENOENT;
+
+ spin_lock(&info->lock);
+ if (info->attr.mq_curmsgs == 0) {
+ spin_unlock(&info->lock);
+ return -EAGAIN;
+ }
+ msg_ptr = mq_peek_index(info, index);
+ if (!msg_ptr) {
+ spin_unlock(&info->lock);
+ return -ENOENT;
+ }
+ k_m_type = msg_ptr->m_type;
+ k_m_ts = msg_ptr->m_ts;
+ spin_unlock(&info->lock);
+
+ k_msg_buffer = alloc_msg(k_m_ts);
+ if (!k_msg_buffer)
+ return -ENOMEM;
+
+ /*
+ * Two spin locks are necessary here. We avoid atomic memory
+ * allocation and premature allocation before confirming that
+ * a message actually exists to peek.
+ */
+ spin_lock(&info->lock);
+ msg_ptr = mq_peek_index(info, index);
+ if (!msg_ptr || msg_ptr->m_type != k_m_type ||
+ msg_ptr->m_ts != k_m_ts) {
+ spin_unlock(&info->lock);
+ free_msg(k_msg_buffer);
+ return -EAGAIN;
+ }
+ if (IS_ERR(copy_msg(msg_ptr, k_msg_buffer, k_m_ts))) {
+ spin_unlock(&info->lock);
+ free_msg(k_msg_buffer);
+ return -EINVAL;
+ }
+ spin_unlock(&info->lock);
+
+ ret = k_msg_buffer->m_ts;
+ if (args.msg_prio && put_user(k_m_type, args.msg_prio)) {
+ free_msg(k_msg_buffer);
+ return -EFAULT;
+ }
+ if (store_msg(args.msg_ptr, k_msg_buffer, k_m_ts)) {
+ free_msg(k_msg_buffer);
+ return -EFAULT;
+ }
+ free_msg(k_msg_buffer);
+ return ret;
+}
+
SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr,
size_t, msg_len, unsigned int, msg_prio,
const struct __kernel_timespec __user *, u_abs_timeout)
@@ -1258,6 +1379,23 @@ SYSCALL_DEFINE5(mq_timedreceive, mqd_t, mqdes, char __user *, u_msg_ptr,
return do_mq_timedreceive(mqdes, u_msg_ptr, msg_len, u_msg_prio, p);
}
+SYSCALL_DEFINE5(mq_timedreceive2, mqd_t, mqdes,
+ struct mq_timedreceive2_args __user *, uargs, unsigned int,
+ flags, const unsigned long, index,
+ const struct __kernel_timespec __user *, u_abs_timeout)
+{
+ struct timespec64 ts, *p = NULL;
+
+ if (u_abs_timeout) {
+ int res = prepare_timeout(u_abs_timeout, &ts);
+
+ if (res)
+ return res;
+ p = &ts;
+ }
+ return do_mq_timedreceive2(mqdes, uargs, flags, index, p);
+}
+
/*
* Notes: the case when user wants us to deregister (with NULL as pointer)
* and he isn't currently owner of notification, will be silently discarded.
@@ -1459,6 +1597,12 @@ struct compat_mq_attr {
compat_long_t __reserved[4]; /* ignored for input, zeroed for output */
};
+struct compat_mq_timedreceive2_args {
+ compat_size_t msg_len;
+ compat_uptr_t msg_prio;
+ compat_uptr_t msg_ptr;
+};
+
static inline int get_compat_mq_attr(struct mq_attr *attr,
const struct compat_mq_attr __user *uattr)
{
@@ -1490,6 +1634,22 @@ static inline int put_compat_mq_attr(const struct mq_attr *attr,
return 0;
}
+static inline int get_compat_mq_args(struct mq_timedreceive2_args *args,
+ struct compat_mq_timedreceive2_args __user *uargs)
+{
+ struct compat_mq_timedreceive2_args v;
+
+ if (copy_from_user(&v, uargs, sizeof(*uargs)))
+ return -EFAULT;
+
+ memset(args, 0, sizeof(*args));
+ args->msg_len = (size_t)compat_ptr(v.msg_len);
+ args->msg_prio = (unsigned int *)compat_ptr(v.msg_prio);
+ args->msg_ptr = (char *)compat_ptr(v.msg_ptr);
+
+ return 0;
+}
+
COMPAT_SYSCALL_DEFINE4(mq_open, const char __user *, u_name,
int, oflag, compat_mode_t, mode,
struct compat_mq_attr __user *, u_attr)
@@ -1583,6 +1743,29 @@ SYSCALL_DEFINE5(mq_timedreceive_time32, mqd_t, mqdes,
}
return do_mq_timedreceive(mqdes, u_msg_ptr, msg_len, u_msg_prio, p);
}
+
+SYSCALL_DEFINE5(mq_timedreceive2_time32, mqd_t, mqdes,
+ struct compat_mq_timedreceive2_args __user *, uargs,
+ unsigned int, flags, const unsigned long, index,
+ const struct old_timespec32 __user *, u_abs_timeout)
+{
+ struct mq_timedreceive2_args args, *pargs = NULL;
+
+ pargs = &args;
+
+ if (get_compat_mq_args(pargs, uargs))
+ return -EFAULT;
+
+ struct timespec64 ts, *p = NULL;
+
+ if (u_abs_timeout) {
+ int res = compat_prepare_timeout(u_abs_timeout, &ts);
+ if (res)
+ return res;
+ p = &ts;
+ }
+ return do_mq_timedreceive2(mqdes, pargs, flags, index, p);
+}
#endif
static const struct inode_operations mqueue_dir_inode_operations = {
diff --git a/ipc/msg.c b/ipc/msg.c
index 62996b97f0ac..6392b11dd7f7 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -1156,7 +1156,7 @@ static long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, in
* not update queue parameters.
*/
if (msgflg & MSG_COPY) {
- msg = copy_msg(msg, copy);
+ msg = copy_msg(msg, copy, msg->m_ts);
goto out_unlock0;
}
diff --git a/ipc/msgutil.c b/ipc/msgutil.c
index e28f0cecb2ec..23f07193f9f3 100644
--- a/ipc/msgutil.c
+++ b/ipc/msgutil.c
@@ -51,7 +51,7 @@ static int __init init_msg_buckets(void)
}
subsys_initcall(init_msg_buckets);
-static struct msg_msg *alloc_msg(size_t len)
+struct msg_msg *alloc_msg(size_t len)
{
struct msg_msg *msg;
struct msg_msgseg **pseg;
@@ -122,39 +122,32 @@ struct msg_msg *load_msg(const void __user *src, size_t len)
free_msg(msg);
return ERR_PTR(err);
}
-#ifdef CONFIG_CHECKPOINT_RESTORE
-struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst)
+
+struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst, size_t len)
{
- struct msg_msgseg *dst_pseg, *src_pseg;
- size_t len = src->m_ts;
- size_t alen;
+ struct msg_msgseg *src_seg, *dst_seg;
+ size_t remaining, chunk;
- if (src->m_ts > dst->m_ts)
+ if (len > src->m_ts)
return ERR_PTR(-EINVAL);
-
- alen = min(len, DATALEN_MSG);
- memcpy(dst + 1, src + 1, alen);
-
- for (dst_pseg = dst->next, src_pseg = src->next;
- src_pseg != NULL;
- dst_pseg = dst_pseg->next, src_pseg = src_pseg->next) {
-
- len -= alen;
- alen = min(len, DATALEN_SEG);
- memcpy(dst_pseg + 1, src_pseg + 1, alen);
+ chunk = min(len, DATALEN_MSG);
+ memcpy(dst + 1, src + 1, chunk);
+ remaining = len - chunk;
+ src_seg = src->next;
+ dst_seg = dst->next;
+ while (remaining > 0 && src_seg && dst_seg) {
+ chunk = min(remaining, DATALEN_SEG);
+ memcpy(dst_seg + 1, src_seg + 1, chunk);
+ remaining -= chunk;
+ src_seg = src_seg->next;
+ dst_seg = dst_seg->next;
}
-
+ if (remaining != 0)
+ return ERR_PTR(-EINVAL);
dst->m_type = src->m_type;
- dst->m_ts = src->m_ts;
-
+ dst->m_ts = src->m_ts;
return dst;
-}
-#else
-struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst)
-{
- return ERR_PTR(-ENOSYS);
-}
-#endif
+ }
int store_msg(void __user *dest, struct msg_msg *msg, size_t len)
{
size_t alen;
diff --git a/ipc/util.h b/ipc/util.h
index a55d6cebe6d3..374abeee79b3 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -197,8 +197,9 @@ int ipc_parse_version(int *cmd);
extern void free_msg(struct msg_msg *msg);
extern struct msg_msg *load_msg(const void __user *src, size_t len);
-extern struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst);
+extern struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst, size_t len);
extern int store_msg(void __user *dest, struct msg_msg *msg, size_t len);
+extern struct msg_msg *alloc_msg(size_t len);
static inline int ipc_checkid(struct kern_ipc_perm *ipcp, int id)
{
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index add3032da16f..e6adc8c4220e 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -391,6 +391,8 @@ COND_SYSCALL(setuid16);
/* restartable sequence */
COND_SYSCALL(rseq);
COND_SYSCALL(rseq_slice_yield);
+COND_SYSCALL(mq_timedreceive2);
+COND_SYSCALL(mq_timedreceive2_time32);
COND_SYSCALL(uretprobe);
COND_SYSCALL(uprobe);
diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
index 1e5d2eeb726d..605a65cfa144 100755
--- a/scripts/checksyscalls.sh
+++ b/scripts/checksyscalls.sh
@@ -104,6 +104,7 @@ cat << EOF
#define __IGNORE_recvmmsg_time64
#define __IGNORE_mq_timedsend_time64
#define __IGNORE_mq_timedreceive_time64
+#define __IGNORE_mq_timedreceive2_time64
#define __IGNORE_semtimedop_time64
#define __IGNORE_rt_sigtimedwait_time64
#define __IGNORE_futex_time64
diff --git a/scripts/syscall.tbl b/scripts/syscall.tbl
index 7a42b32b6577..57b711f93756 100644
--- a/scripts/syscall.tbl
+++ b/scripts/syscall.tbl
@@ -412,3 +412,6 @@
469 common file_setattr sys_file_setattr
470 common listns sys_listns
471 common rseq_slice_yield sys_rseq_slice_yield
+472 32 mq_timedreceive2_time64 sys_mq_timedreceive2
+473 64 mq_timedreceive2 sys_mq_timedreceive2
+473 time32 mq_timedreceive2 sys_mq_timedreceive2_time32
diff --git a/tools/testing/selftests/ipc/.gitignore b/tools/testing/selftests/ipc/.gitignore
index 9ed280e4c704..fe609d98ecb2 100644
--- a/tools/testing/selftests/ipc/.gitignore
+++ b/tools/testing/selftests/ipc/.gitignore
@@ -1,3 +1,4 @@
# SPDX-License-Identifier: GPL-2.0-only
msgque_test
msgque
+mq_peek
diff --git a/tools/testing/selftests/ipc/Makefile b/tools/testing/selftests/ipc/Makefile
index 50e9c299fc4a..fa9d4f500783 100644
--- a/tools/testing/selftests/ipc/Makefile
+++ b/tools/testing/selftests/ipc/Makefile
@@ -1,6 +1,8 @@
# SPDX-License-Identifier: GPL-2.0
uname_M := $(shell uname -m 2>/dev/null || echo not)
ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/i386/)
+CC = gcc
+CFLAGS = -static -O2
ifeq ($(ARCH),i386)
ARCH := x86
CFLAGS := -DCONFIG_X86_32 -D__i386__
@@ -12,7 +14,8 @@ endif
CFLAGS += $(KHDR_INCLUDES)
-TEST_GEN_PROGS := msgque
+TEST_GEN_PROGS := msgque mq_peek
+LDLIBS += -lrt -lpthread
include ../lib.mk
diff --git a/tools/testing/selftests/ipc/mq_peek.c b/tools/testing/selftests/ipc/mq_peek.c
new file mode 100644
index 000000000000..77fcb50fdbcd
--- /dev/null
+++ b/tools/testing/selftests/ipc/mq_peek.c
@@ -0,0 +1,794 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * mq_peek.c - Selftest for mq_timedreceive2(MQ_PEEK)
+ *
+ * Tests the peek-without-dequeue extension to POSIX message queues:
+ * - Correct priority-rank indexed access (index 0 = highest priority)
+ * - FIFO ordering within same priority level
+ * - Non-destructive semantics (queue is never modified on peek)
+ * - All error paths (-EBADF, -EMSGSIZE, -EFAULT, -EAGAIN, -ENOENT)
+ * - Large (multi-segment) message payload copy
+ * - Concurrent peek + receive / peek + send races
+ */
+
+#include "linux/array_size.h"
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <errno.h>
+#include <pthread.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <mqueue.h>
+#include <time.h>
+
+#include "kselftest.h"
+
+#ifndef __NR_mq_timedreceive2
+#if defined(__x86_64__)
+#define __NR_mq_timedreceive2 548
+#elif defined(__aarch64__)
+#define __NR_mq_timedreceive2 548
+#elif defined(__riscv)
+#define __NR_mq_timedreceive2 548
+#else
+#define __NR_mq_timedreceive2 548
+#endif
+#endif
+
+#define MQ_PEEK 2U
+
+struct mq_timedreceive2_args {
+ size_t msg_len;
+ unsigned int *msg_prio;
+ char *msg_ptr;
+};
+
+static long mq_timedreceive2(mqd_t mqdes, struct mq_timedreceive2_args *uargs,
+ unsigned int flags, unsigned long index,
+ const struct timespec *timeout)
+{
+ return syscall(__NR_mq_timedreceive2, (long)mqdes, uargs, (long)flags,
+ index, timeout);
+}
+
+#define MQ_NAME_PREFIX "/mq_peek_test_"
+#define MAX_MSG_SIZE 128
+#define LARGE_MSG_SIZE 4064
+#define MQ_MAXMSG 16
+
+#define PRIO_HIGH 9
+#define PRIO_MED 5
+#define PRIO_LOW 1
+
+static mqd_t open_queue(const char *suffix, long msgsize)
+{
+ char name[64];
+ struct mq_attr attr = {
+ .mq_flags = 0,
+ .mq_maxmsg = MQ_MAXMSG,
+ .mq_msgsize = msgsize,
+ .mq_curmsgs = 0,
+ };
+ mqd_t mqd;
+
+ snprintf(name, sizeof(name), "%s%s", MQ_NAME_PREFIX, suffix);
+ mq_unlink(name);
+
+ mqd = mq_open(name, O_NONBLOCK | O_RDWR | O_CREAT | O_EXCL, 0600, &attr);
+ if (mqd == (mqd_t)-1) {
+ ksft_test_result_fail("mq_open(%s): %m\n", name);
+ ksft_exit_fail();
+ }
+
+ mq_unlink(name);
+ return mqd;
+}
+
+static void send_msg(mqd_t mqd, unsigned int prio, const char *text, size_t len)
+{
+ if (mq_send(mqd, text, len, prio) != 0) {
+ ksft_test_result_fail("mq_send(prio=%u): %m\n", prio);
+ ksft_exit_fail();
+ }
+}
+
+static long peek(mqd_t mqd, unsigned long index, char *buf, size_t bufsz,
+ unsigned int *prio)
+{
+ struct mq_timedreceive2_args args = {
+ .msg_len = bufsz,
+ .msg_prio = prio,
+ .msg_ptr = buf,
+ };
+ return mq_timedreceive2(mqd, &args, MQ_PEEK, index, NULL);
+}
+
+static long queue_depth(mqd_t mqd)
+{
+ struct mq_attr attr;
+
+ if (mq_getattr(mqd, &attr) != 0)
+ return -1;
+ return attr.mq_curmsgs;
+}
+
+static void test_peek_empty_queue(void)
+{
+ mqd_t mqd = open_queue("empty", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+
+ ret = peek(mqd, 0, buf, sizeof(buf), &prio);
+ if (ret == -1 && errno == EAGAIN)
+ ksft_test_result_pass("peek on empty queue [EAGAIN]\n");
+ else
+ ksft_test_result_fail("peek on empty queue: expected EAGAIN, got ret=%ld errno=%d (%m)\n",
+ ret, errno);
+
+ mq_close(mqd);
+}
+
+static void test_peek_invalid_fd(void)
+{
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+
+ ret = peek((mqd_t)-1, 0, buf, sizeof(buf), &prio);
+ if (ret == -1 && errno == EBADF)
+ ksft_test_result_pass("peek invalid fd [ EBADF]\n");
+ else
+ ksft_test_result_fail("peek invalid fd: expected EBADF, got ret=%ld errno=%d\n",
+ ret, errno);
+}
+
+
+static void test_peek_non_mqueue_fd(void)
+{
+ int pipefd[2];
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+
+ if (pipe(pipefd) != 0) {
+ ksft_test_result_skip("pipe() failed, skipping non-mqueue-fd test\n");
+ return;
+ }
+
+ ret = peek((mqd_t)pipefd[0], 0, buf, sizeof(buf), &prio);
+ if (ret == -1 && errno == EBADF)
+ ksft_test_result_pass("peek on pipe fd [EBADF]\n");
+ else
+ ksft_test_result_fail("peek non-mqueue fd: expected EBADF, got ret=%ld errno=%d\n",
+ ret, errno);
+
+ close(pipefd[0]);
+ close(pipefd[1]);
+}
+
+
+static void test_peek_writeonly_fd(void)
+{
+ char name[] = "/ksft_mq_peek_wo";
+ struct mq_attr attr = { .mq_maxmsg = 4, .mq_msgsize = MAX_MSG_SIZE };
+ mqd_t rw, wo;
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+
+ mq_unlink(name);
+ rw = mq_open(name, O_RDWR | O_CREAT, 0600, &attr);
+ if (rw == (mqd_t)-1) {
+ ksft_test_result_skip("mq_open RW failed: %m\n");
+ return;
+ }
+ wo = mq_open(name, O_WRONLY);
+ mq_unlink(name);
+
+ if (wo == (mqd_t)-1) {
+ ksft_test_result_skip("mq_open WO failed: %m\n");
+ mq_close(rw);
+ return;
+ }
+
+ send_msg(rw, PRIO_HIGH, "x", 1);
+
+ ret = peek(wo, 0, buf, sizeof(buf), &prio);
+ if (ret == -1 && errno == EBADF)
+ ksft_test_result_pass("peek on O_WRONLY fd [EBADF]\n");
+ else
+ ksft_test_result_fail("peek WO fd: expected EBADF, got ret=%ld errno=%d\n",
+ ret, errno);
+
+ mq_close(wo);
+ mq_close(rw);
+}
+
+
+static void test_peek_buffer_too_small(void)
+{
+ mqd_t mqd = open_queue("small", MAX_MSG_SIZE);
+ char tiny[1]; /* deliberately too small */
+ unsigned int prio;
+ struct mq_timedreceive2_args args = {
+ .msg_len = sizeof(tiny),
+ .msg_prio = &prio,
+ .msg_ptr = tiny,
+ };
+ long ret;
+
+ send_msg(mqd, PRIO_HIGH, "hello", 5);
+
+ ret = mq_timedreceive2(mqd, &args, MQ_PEEK, 0, NULL);
+ if (ret == -1 && errno == EMSGSIZE)
+ ksft_test_result_pass("peek with small buf [EMSGSIZE]\n");
+ else
+ ksft_test_result_fail("peek small buf: expected EMSGSIZE, got ret=%ld errno=%d\n",
+ ret, errno);
+
+ mq_close(mqd);
+}
+
+
+
+
+static void test_peek_bad_msg_ptr(void)
+{
+ mqd_t mqd = open_queue("bad_ptr", MAX_MSG_SIZE);
+ unsigned int prio;
+
+ struct mq_timedreceive2_args args = {
+ .msg_len = MAX_MSG_SIZE,
+ .msg_prio = &prio,
+ .msg_ptr = (char *)0x1,
+ };
+ long ret;
+ send_msg(mqd, PRIO_HIGH, "payload", 7);
+ ret = mq_timedreceive2(mqd, &args, MQ_PEEK, 0, NULL);
+ if (ret == -1 && errno == EFAULT)
+ ksft_test_result_pass("peek bad msg_ptr [EFAULT]\n");
+ else
+ ksft_test_result_fail("peek bad msg_ptr: expected EFAULT, got ret=%ld errno=%d\n",
+ ret, errno);
+
+ mq_close(mqd);
+}
+
+
+static void test_peek_index_out_of_range(void)
+{
+ mqd_t mqd = open_queue("oob", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+ send_msg(mqd, PRIO_MED, "one", 3);
+ ret = peek(mqd, 1, buf, sizeof(buf), &prio);
+ if (ret == -1 && errno == ENOENT)
+ ksft_test_result_pass("peek OOB index [ENOENT]\n");
+ else
+ ksft_test_result_fail("peek OOB: expected ENOENT, got ret=%ld errno=%d\n",
+ ret, errno);
+
+ mq_close(mqd);
+}
+
+
+static void test_peek_basic_data(void)
+{
+ mqd_t mqd = open_queue("basic", MAX_MSG_SIZE);
+ const char *payload = "peek-test-payload";
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio = 0;
+ long ret;
+
+ send_msg(mqd, PRIO_HIGH, payload, strlen(payload));
+
+ memset(buf, 0, sizeof(buf));
+ ret = peek(mqd, 0, buf, sizeof(buf), &prio);
+
+ if (ret < 0) {
+ ksft_test_result_fail("basic peek failed: ret=%ld errno=%d (%m)\n", ret, errno);
+ goto out;
+ }
+ if ((size_t)ret != strlen(payload)) {
+ ksft_test_result_fail("basic peek: wrong size %ld (expected %zu)\n", ret, strlen(payload));
+ goto out;
+ }
+ if (memcmp(buf, payload, strlen(payload)) != 0) {
+ ksft_test_result_fail("basic peek: payload mismatch\n");
+ goto out;
+ }
+ if (prio != PRIO_HIGH) {
+ ksft_test_result_fail("basic peek: wrong prio %u (expected %d)\n", prio, PRIO_HIGH);
+ goto out;
+ }
+ ksft_test_result_pass("basic peek: correct data and priority\n");
+out:
+ mq_close(mqd);
+}
+
+
+static void test_peek_nondestructive(void)
+{
+ mqd_t mqd = open_queue("nodestr", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ int i;
+
+ send_msg(mqd, PRIO_HIGH, "A", 1);
+ send_msg(mqd, PRIO_MED, "B", 1);
+ send_msg(mqd, PRIO_LOW, "C", 1);
+
+ if (queue_depth(mqd) != 3) {
+ ksft_test_result_fail("initial depth != 3\n");
+ mq_close(mqd);
+ return;
+ }
+
+ for (i = 0; i < 10; i++) {
+ peek(mqd, 0, buf, sizeof(buf), &prio);
+ peek(mqd, 1, buf, sizeof(buf), &prio);
+ peek(mqd, 2, buf, sizeof(buf), &prio);
+ }
+
+ if (queue_depth(mqd) == 3)
+ ksft_test_result_pass(
+ "peek is non-destructive (depth stays 3)\n");
+ else
+ ksft_test_result_fail("peek modified queue: depth=%ld (expected 3)\n", queue_depth(mqd));
+
+ mq_close(mqd);
+}
+
+
+static void test_peek_priority_order(void)
+{
+ mqd_t mqd = open_queue("prio_order", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+ int pass = 1;
+
+ send_msg(mqd, PRIO_LOW, "low", 3);
+ send_msg(mqd, PRIO_HIGH, "high", 4);
+ send_msg(mqd, PRIO_MED, "med", 3);
+
+ /* index 0 must return highest priority */
+ ret = peek(mqd, 0, buf, sizeof(buf), &prio);
+ if (ret < 0 || prio != PRIO_HIGH) {
+ ksft_test_result_fail(
+ "prio_order index0: prio=%u ret=%ld errno=%d\n", prio,
+ ret, errno);
+ pass = 0;
+ }
+ if (pass && memcmp(buf, "high", 4) != 0) {
+ ksft_test_result_fail("prio_order index0: wrong payload\n");
+ pass = 0;
+ }
+
+ /* index 1 must return medium priority */
+ ret = peek(mqd, 1, buf, sizeof(buf), &prio);
+ if (pass && (ret < 0 || prio != PRIO_MED)) {
+ ksft_test_result_fail("prio_order index1: prio=%u ret=%ld\n",
+ prio, ret);
+ pass = 0;
+ }
+ if (pass && memcmp(buf, "med", 3) != 0) {
+ ksft_test_result_fail("prio_order index1: wrong payload\n");
+ pass = 0;
+ }
+
+ /* index 2 must return lowest priority */
+ ret = peek(mqd, 2, buf, sizeof(buf), &prio);
+ if (pass && (ret < 0 || prio != PRIO_LOW)) {
+ ksft_test_result_fail("prio_order index2: prio=%u ret=%ld\n",
+ prio, ret);
+ pass = 0;
+ }
+ if (pass && memcmp(buf, "low", 3) != 0) {
+ ksft_test_result_fail("prio_order index2: wrong payload\n");
+ pass = 0;
+ }
+
+ if (pass)
+ ksft_test_result_pass(
+ "priority ordering: index0=HIGH, index1=MED, index2=LOW\n");
+
+ mq_close(mqd);
+}
+
+
+static void test_peek_fifo_within_priority(void)
+{
+ mqd_t mqd = open_queue("fifo", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+ int pass = 1;
+
+ send_msg(mqd, PRIO_HIGH, "first", 5);
+ send_msg(mqd, PRIO_HIGH, "second", 6);
+ send_msg(mqd, PRIO_HIGH, "third", 5);
+
+ memset(buf, 0, sizeof(buf));
+ ret = peek(mqd, 0, buf, sizeof(buf), &prio);
+ if (ret < 0 || memcmp(buf, "first", 5) != 0) {
+ ksft_test_result_fail(
+ "FIFO peek[0]: expected 'first', got '%.*s' ret=%ld\n",
+ (int)ret, buf, ret);
+ pass = 0;
+ }
+
+ if (pass) {
+ char rbuf[MAX_MSG_SIZE];
+ unsigned int rprio;
+ ssize_t r = mq_receive(mqd, rbuf, sizeof(rbuf), &rprio);
+ if (r < 0 || memcmp(rbuf, "first", 5) != 0) {
+ ksft_test_result_fail("mq_receive 'first' failed\n");
+ pass = 0;
+ }
+ }
+
+ if (pass) {
+ memset(buf, 0, sizeof(buf));
+ ret = peek(mqd, 0, buf, sizeof(buf), &prio);
+ if (ret < 0 || memcmp(buf, "second", 6) != 0) {
+ ksft_test_result_fail("FIFO peek after receive: expected 'second', got '%.*s'\n",
+ (int)ret, buf);
+ pass = 0;
+ }
+}
+
+ if (pass)
+ ksft_test_result_pass("FIFO within same priority is correct\n");
+
+ mq_close(mqd);
+}
+
+
+static void test_peek_all_indices(void)
+{
+ const unsigned int prios[] = { 2, 7, 4, 9, 1, 6 };
+ const int N = (int)(sizeof(prios) / sizeof(prios[0]));
+ mqd_t mqd = open_queue("all_idx", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ char expected_payload[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+ int i, pass = 1;
+ unsigned int sorted[6];
+
+ for (i = 0; i < N; i++) {
+ snprintf(expected_payload, sizeof(expected_payload),
+ "msg_prio_%u", prios[i]);
+ send_msg(mqd, prios[i], expected_payload,
+ strlen(expected_payload));
+ sorted[i] = prios[i];
+ }
+
+ for (i = 0; i < N - 1; i++) {
+ int j;
+ for (j = i + 1; j < N; j++) {
+ if (sorted[j] > sorted[i]) {
+ unsigned int tmp = sorted[i];
+ sorted[i] = sorted[j];
+ sorted[j] = tmp;
+ }
+ }
+ }
+
+ for (i = 0; i < N && pass; i++) {
+ memset(buf, 0, sizeof(buf));
+ ret = peek(mqd, (unsigned long)i, buf, sizeof(buf), &prio);
+ if (ret < 0) {
+ ksft_test_result_fail("all_indices peek[%d] failed: ret=%ld errno=%d\n",
+ i, ret, errno);
+ pass = 0;
+ break;
+ }
+ if (prio != sorted[i]) {
+ ksft_test_result_fail("all_indices peek[%d]: prio=%u expected=%u\n",
+ i, prio, sorted[i]);
+ pass = 0;
+ }
+
+ snprintf(expected_payload, sizeof(expected_payload),
+ "msg_prio_%u", sorted[i]);
+ if (memcmp(buf, expected_payload, strlen(expected_payload))) {
+ ksft_test_result_fail("all_indices peek[%d]: payload mismatch\n", i);
+ pass = 0;
+ }
+ }
+
+ if (pass && queue_depth(mqd) != N) {
+ ksft_test_result_fail("all_indices: depth=%ld expected=%d after peek\n",
+ queue_depth(mqd), N);
+ pass = 0;
+ }
+
+ if (pass) {
+ ret = peek(mqd, (unsigned long)N, buf, sizeof(buf), &prio);
+ if (!(ret == -1 && errno == ENOENT)) {
+ ksft_test_result_fail("all_indices OOB[%d]: expected ENOENT, got ret=%ld errno=%d\n",
+ N, ret, errno);
+ pass = 0;
+ }
+ }
+
+ if (pass)
+ ksft_test_result_pass("all-indices: correct prio order + OOB ENOENT\n");
+
+ mq_close(mqd);
+}
+
+static void test_peek_large_message(void)
+{
+ mqd_t mqd = open_queue("large", LARGE_MSG_SIZE);
+ char *send_buf, *recv_buf;
+ unsigned int prio = 0;
+ long ret;
+ int pass = 1;
+
+ send_buf = malloc(LARGE_MSG_SIZE);
+ recv_buf = calloc(1, LARGE_MSG_SIZE);
+ if (!send_buf || !recv_buf) {
+ ksft_test_result_skip("OOM allocating large message buffers\n");
+ goto out;
+ }
+
+ for (int i = 0; i < LARGE_MSG_SIZE; i++)
+ send_buf[i] = (char)(i & 0xFF);
+
+ send_msg(mqd, PRIO_HIGH, send_buf, LARGE_MSG_SIZE);
+
+ ret = peek(mqd, 0, recv_buf, LARGE_MSG_SIZE, &prio);
+ if (ret != LARGE_MSG_SIZE) {
+ ksft_test_result_fail("large msg peek: ret=%ld expected=%d\n",
+ ret, LARGE_MSG_SIZE);
+ pass = 0;
+ }
+ if (pass && memcmp(send_buf, recv_buf, LARGE_MSG_SIZE) != 0) {
+ ksft_test_result_fail("large msg peek: payload mismatch\n");
+ pass = 0;
+ }
+ if (pass && prio != PRIO_HIGH) {
+ ksft_test_result_fail("large msg peek: prio=%u expected=%d\n",
+ prio, PRIO_HIGH);
+ pass = 0;
+ }
+ if (pass && queue_depth(mqd) != 1) {
+ ksft_test_result_fail(
+ "large msg peek: queue modified (depth=%ld)\n",
+ queue_depth(mqd));
+ pass = 0;
+ }
+ if (pass)
+ ksft_test_result_pass(
+ "large (%d B) multi-segment peek: correct\n",
+ LARGE_MSG_SIZE);
+out:
+ free(send_buf);
+ free(recv_buf);
+ mq_close(mqd);
+}
+
+static void test_no_peek_flag_is_receive(void)
+{
+ mqd_t mqd = open_queue("nopeek", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio = 0;
+ struct mq_timedreceive2_args args = {
+ .msg_len = sizeof(buf),
+ .msg_prio = &prio,
+ .msg_ptr = buf,
+ };
+ long ret;
+
+ send_msg(mqd, PRIO_HIGH, "consume-me", 10);
+
+ ret = mq_timedreceive2(mqd, &args, 0, 0, NULL);
+ if (ret < 0) {
+ ksft_test_result_fail("no-peek receive failed: ret=%ld errno=%d\n", ret, errno);
+ mq_close(mqd);
+ return;
+ }
+ if (queue_depth(mqd) != 0)
+ ksft_test_result_fail("no-peek: queue still has messages (depth=%ld)\n", queue_depth(mqd));
+ else
+ ksft_test_result_pass("without MQ_PEEK the message is consumed normally\n");
+
+ mq_close(mqd);
+}
+
+
+struct race_ctx {
+ mqd_t mqd;
+ int errors;
+};
+
+static void *receiver_thread(void *arg)
+{
+ struct race_ctx *ctx = arg;
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ ssize_t r;
+
+ while ((r = mq_receive(ctx->mqd, buf, sizeof(buf), &prio)) > 0)
+ ;
+
+ return NULL;
+}
+
+static void test_peek_concurrent_receive(void)
+{
+ struct race_ctx ctx;
+ pthread_t tid;
+ char buf[MAX_MSG_SIZE];
+ unsigned int prio;
+ long ret;
+ int i;
+
+ ctx.mqd = open_queue("concurrent", MAX_MSG_SIZE);
+ ctx.errors = 0;
+
+
+ for (i = 0; i < MQ_MAXMSG; i++) {
+ char payload[32];
+ snprintf(payload, sizeof(payload), "msg%d", i);
+ send_msg(ctx.mqd, (unsigned int)(i % 5) + 1, payload,
+ strlen(payload));
+ }
+
+ if (pthread_create(&tid, NULL, receiver_thread, &ctx) != 0) {
+ ksft_test_result_skip("pthread_create failed\n");
+ mq_close(ctx.mqd);
+ return;
+ }
+
+ /*
+ Peek repeatedly.The queue is being drained concurrently.
+ */
+ for (i = 0; i < 200; i++) {
+ ret = peek(ctx.mqd, (unsigned long)(i % 4), buf, sizeof(buf),
+ &prio);
+ if (ret < 0 && errno != EAGAIN && errno != ENOENT) {
+ ctx.errors++;
+ }
+ }
+
+ pthread_join(tid, NULL);
+
+ if (ctx.errors == 0)
+ ksft_test_result_pass("concurrent peek+receive: no unexpected errors\n");
+ else
+ ksft_test_result_fail("concurrent peek+receive: %d unexpected errors\n", ctx.errors);
+
+ mq_close(ctx.mqd);
+}
+
+static void test_peek_null_prio_ptr(void)
+{
+ mqd_t mqd = open_queue("null_prio", MAX_MSG_SIZE);
+ char buf[MAX_MSG_SIZE];
+ struct mq_timedreceive2_args args = {
+ .msg_len = sizeof(buf),
+ .msg_prio = NULL,
+ .msg_ptr = buf,
+ };
+ long ret;
+
+ send_msg(mqd, PRIO_MED, "no-prio-needed", 14);
+
+ ret = mq_timedreceive2(mqd, &args, MQ_PEEK, 0, NULL);
+ if (ret >= 0)
+ ksft_test_result_pass("peek with NULL msg_prio ptr: OK\n");
+ else
+ ksft_test_result_fail("peek NULL msg_prio: ret=%ld errno=%d (%m)\n", ret, errno);
+
+ mq_close(mqd);
+}
+
+
+static void test_peek_priority_matches_receive(void)
+{
+ mqd_t mqd = open_queue("prio_match", MAX_MSG_SIZE);
+ char peek_buf[MAX_MSG_SIZE], recv_buf[MAX_MSG_SIZE];
+ unsigned int peek_prio = 0, recv_prio = 0;
+ long peek_ret;
+ ssize_t recv_ret;
+ int pass = 1;
+
+ send_msg(mqd, PRIO_MED, "consistent-prio", 15);
+
+ peek_ret = peek(mqd, 0, peek_buf, sizeof(peek_buf), &peek_prio);
+ if (peek_ret < 0) {
+ ksft_test_result_fail("peek failed: %m\n");
+ mq_close(mqd);
+ return;
+ }
+
+ recv_ret = mq_receive(mqd, recv_buf, sizeof(recv_buf), &recv_prio);
+ if (recv_ret < 0) {
+ ksft_test_result_fail("mq_receive failed: %m\n");
+ mq_close(mqd);
+ return;
+ }
+
+ if (peek_prio != recv_prio) {
+ ksft_test_result_fail("prio mismatch: peek=%u receive=%u\n",
+ peek_prio, recv_prio);
+ pass = 0;
+ }
+ if (pass && peek_ret != recv_ret) {
+ ksft_test_result_fail("size mismatch: peek=%ld receive=%zd\n",
+ peek_ret, recv_ret);
+ pass = 0;
+ }
+ if (pass && memcmp(peek_buf, recv_buf, (size_t)recv_ret) != 0) {
+ ksft_test_result_fail("payload mismatch between peek and receive\n");
+ pass = 0;
+ }
+ if (pass)
+ ksft_test_result_pass("peeked priority/payload matches mq_receive output\n");
+
+ mq_close(mqd);
+}
+
+
+
+static const struct {
+ const char *name;
+ void (*fn)(void);
+} tests[] = {
+ { "empty queue → EAGAIN", test_peek_empty_queue },
+ { "invalid fd → EBADF", test_peek_invalid_fd },
+ { "non-mqueue fd → EBADF", test_peek_non_mqueue_fd },
+ { "O_WRONLY fd → EBADF", test_peek_writeonly_fd },
+ { "buffer too small → EMSGSIZE", test_peek_buffer_too_small },
+ { "bad msg_ptr → EFAULT", test_peek_bad_msg_ptr },
+ { "OOB index → ENOENT", test_peek_index_out_of_range },
+ { "basic data+prio correctness", test_peek_basic_data },
+ { "non-destructive semantics", test_peek_nondestructive },
+ { "priority ordering across indices", test_peek_priority_order },
+ { "FIFO within same priority", test_peek_fifo_within_priority },
+ { "all distinct priority indices", test_peek_all_indices },
+ { "large multi-segment message", test_peek_large_message },
+ { "no MQ_PEEK → normal receive", test_no_peek_flag_is_receive },
+ { "concurrent peek + receive", test_peek_concurrent_receive },
+ { "NULL msg_prio ptr", test_peek_null_prio_ptr },
+ { "peeked prio matches mq_receive",
+ test_peek_priority_matches_receive },
+};
+
+int main(void)
+{
+ unsigned int i;
+ long sc_ret;
+
+ ksft_print_header();
+ ksft_set_plan(sizeof(tests) / sizeof(tests[0]));
+
+
+ {
+ struct mq_timedreceive2_args probe_args = { 0 };
+ sc_ret = mq_timedreceive2((mqd_t)-1, &probe_args, MQ_PEEK, 0,
+ NULL);
+ if (sc_ret == -1 && errno == ENOSYS)
+ ksft_exit_skip("mq_timedreceive2 syscall not available "
+ "(NR=%d ENOSYS) — is the kernel too old?\n",
+ __NR_mq_timedreceive2);
+ }
+
+ for (i = 0; i < ARRAY_SIZE(tests); i++) {
+ ksft_print_msg("--- [%02u] %s ---\n", i + 1, tests[i].name);
+ tests[i].fn();
+ }
+
+ return ksft_get_fail_cnt() ? 1 : 0;
+}
--
2.43.0