* [PATCH v1 1/4] IPC: Added New system call do_mq_timedreceive2() for non-destructive peek on posix mqueue
2026-03-15 4:07 [PATCH 0/4] Add new system call for non-destructive peek and inspection to posix ipc mqueue Mathura_Kumar
@ 2026-03-15 4:07 ` Mathura_Kumar
2026-03-15 14:35 ` kernel test robot
` (3 more replies)
2026-03-15 4:07 ` [PATCH v1 2/4] IPC: Added system call number in all most common arch Mathura_Kumar
` (2 subsequent siblings)
3 siblings, 4 replies; 10+ messages in thread
From: Mathura_Kumar @ 2026-03-15 4:07 UTC (permalink / raw)
To: brauner; +Cc: academic1mathura, linux-arch, linux-kernel, viro
Signed-off-by: Mathura_Kumar <academic1mathura@gmail.com>
---
include/linux/compat.h | 6 +-
include/linux/syscalls.h | 6 +
include/uapi/asm-generic/unistd.h | 7 +-
include/uapi/linux/mqueue.h | 18 ++-
ipc/mqueue.c | 186 ++++++++++++++++++++++++++++--
ipc/msg.c | 2 +-
ipc/msgutil.c | 48 ++++----
ipc/util.h | 3 +-
kernel/sys_ni.c | 1 +
9 files changed, 235 insertions(+), 42 deletions(-)
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 56cebaff0c91..9f5ca26e76d8 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -22,6 +22,7 @@
#include <asm/compat.h>
#include <asm/siginfo.h>
#include <asm/signal.h>
+#include <linux/mqueue.h>
#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
/*
@@ -801,8 +802,9 @@ asmlinkage long compat_sys_pwritev64v2(unsigned long fd,
const struct iovec __user *vec,
unsigned long vlen, loff_t pos, rwf_t flags);
#endif
-
-
+asmlinkage long compat_sys_mq_timedreceive2(mqd_t mqdes, struct compat_mq_timedreceive2_args __user *uargs,
+ unsigned int flags, unsigned long index,
+ struct old_timespec32 __user *abs_timeout);
/*
* Deprecated system calls which are still defined in
* include/uapi/asm-generic/unistd.h and wanted by >= 1 arch
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 02bd6ddb6278..993e570c90ab 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -79,6 +79,7 @@ struct mnt_id_req;
struct ns_id_req;
struct xattr_args;
struct file_attr;
+struct mq_timedreceive2_args;
#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -93,6 +94,7 @@ 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 +748,10 @@ 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_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..200ee7fde5c4 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -863,9 +863,12 @@ __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
+#define __NR_mq_timedreceive2 472
+__SC_COMP(__NR_mq_timedreceive2, sys_mq_timedreceive2,
+ compat_sys_mq_timedreceive2)
+#undef __NR_syscalls
+#define __NR_syscalls 473
/*
* 32 bit systems traditionally used different
* syscalls for off_t and loff_t arguments, while
diff --git a/include/uapi/linux/mqueue.h b/include/uapi/linux/mqueue.h
index b516b66840ad..9a4f5dfa7a68 100644
--- a/include/uapi/linux/mqueue.h
+++ b/include/uapi/linux/mqueue.h
@@ -18,7 +18,6 @@
#ifndef _LINUX_MQUEUE_H
#define _LINUX_MQUEUE_H
-
#include <linux/types.h>
#define MQ_PRIO_MAX 32768
@@ -33,6 +32,23 @@ struct mq_attr {
__kernel_long_t __reserved[4]; /* ignored for input, zeroed for output */
};
+struct mq_timedreceive2_args {
+ size_t msg_len;
+ unsigned int *msg_prio;
+ char *msg_ptr;
+};
+
+#ifdef CONFIG_COMPAT
+#include <asm/compat.h>
+
+struct compat_mq_timedreceive2_args {
+ compat_size_t msg_len;
+ compat_uptr_t msg_prio;
+ compat_uptr_t msg_ptr;
+};
+
+#endif
+
/*
* SIGEV_THREAD implementation:
* SIGEV_THREAD must be implemented in user space. If SIGEV_THREAD is passed
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 4798b375972b..78dc414967a2 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
@@ -1230,6 +1231,115 @@ 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 *args,
+ unsigned int flags, unsigned long index,
+ struct timespec64 *ts)
+{
+ 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 (!(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 are avoiding 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 +1368,27 @@ 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 mq_timedreceive2_args args;
+ struct timespec64 ts, *p = NULL;
+
+ if (copy_from_user(&args, uargs, sizeof(args)))
+ return -EFAULT;
+
+ if (u_abs_timeout) {
+ int res = prepare_timeout(u_abs_timeout, &ts);
+
+ if (res)
+ return res;
+ p = &ts;
+ }
+ return do_mq_timedreceive2(mqdes, &args, 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.
@@ -1449,6 +1580,17 @@ SYSCALL_DEFINE3(mq_getsetattr, mqd_t, mqdes,
return 0;
}
+#ifdef CONFIG_COMPAT_32BIT_TIME
+static int compat_prepare_timeout(const struct old_timespec32 __user *p,
+ struct timespec64 *ts)
+{
+ if (get_old_timespec32(ts, p))
+ return -EFAULT;
+ if (!timespec64_valid(ts))
+ return -EINVAL;
+ return 0;
+}
+
#ifdef CONFIG_COMPAT
struct compat_mq_attr {
@@ -1490,6 +1632,22 @@ 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(v)))
+ return -EFAULT;
+
+ memset(args, 0, sizeof(*args));
+ args->msg_len = (size_t)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)
@@ -1541,19 +1699,30 @@ COMPAT_SYSCALL_DEFINE3(mq_getsetattr, mqd_t, mqdes,
return -EFAULT;
return 0;
}
-#endif
-#ifdef CONFIG_COMPAT_32BIT_TIME
-static int compat_prepare_timeout(const struct old_timespec32 __user *p,
- struct timespec64 *ts)
+COMPAT_SYSCALL_DEFINE5(mq_timedreceive2, 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)
{
- if (get_old_timespec32(ts, p))
+ struct mq_timedreceive2_args args;
+ struct timespec64 ts, *p = NULL;
+
+ if (get_compat_mq_args(&args, uargs))
return -EFAULT;
- if (!timespec64_valid(ts))
- return -EINVAL;
- return 0;
+
+ if (u_abs_timeout) {
+ int res = compat_prepare_timeout(u_abs_timeout, &ts);
+
+ if (res)
+ return res;
+ p = &ts;
+ }
+ return do_mq_timedreceive2(mqdes, &args, flags, index, p);
}
+#endif
+
SYSCALL_DEFINE5(mq_timedsend_time32, mqd_t, mqdes,
const char __user *, u_msg_ptr,
unsigned int, msg_len, unsigned int, msg_prio,
@@ -1583,6 +1752,7 @@ SYSCALL_DEFINE5(mq_timedreceive_time32, mqd_t, mqdes,
}
return do_mq_timedreceive(mqdes, u_msg_ptr, msg_len, u_msg_prio, 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..c5536ce47cc2 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 +122,33 @@ 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..658d6b8274b3 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -391,6 +391,7 @@ COND_SYSCALL(setuid16);
/* restartable sequence */
COND_SYSCALL(rseq);
COND_SYSCALL(rseq_slice_yield);
+COND_SYSCALL(mq_timedreceive2);
COND_SYSCALL(uretprobe);
COND_SYSCALL(uprobe);
--
2.43.0
^ permalink raw reply related [flat|nested] 10+ messages in thread* [PATCH v1 3/4] IPC: Prepared Documentation and test
2026-03-15 4:07 [PATCH 0/4] Add new system call for non-destructive peek and inspection to posix ipc mqueue Mathura_Kumar
2026-03-15 4:07 ` [PATCH v1 1/4] IPC: Added New system call do_mq_timedreceive2() for non-destructive peek on posix mqueue Mathura_Kumar
2026-03-15 4:07 ` [PATCH v1 2/4] IPC: Added system call number in all most common arch Mathura_Kumar
@ 2026-03-15 4:07 ` Mathura_Kumar
2026-03-15 4:08 ` [PATCH v1 4/4] IPC:Added entry in performance tools for new system call Mathura_Kumar
3 siblings, 0 replies; 10+ messages in thread
From: Mathura_Kumar @ 2026-03-15 4:07 UTC (permalink / raw)
To: brauner; +Cc: academic1mathura, linux-arch, linux-kernel, viro
Signed-off-by: Mathura_Kumar <academic1mathura@gmail.com>
---
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/ipc.rst | 222 +++++++
tools/testing/selftests/ipc/.gitignore | 1 +
tools/testing/selftests/ipc/Makefile | 9 +-
tools/testing/selftests/ipc/mq_peek.c | 785 +++++++++++++++++++++++++
5 files changed, 1017 insertions(+), 1 deletion(-)
create mode 100644 Documentation/userspace-api/ipc.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..bf747a91e74a 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -22,6 +22,7 @@ System calls
ioctl/index
mseal
rseq
+ ipc
Security-related interfaces
===========================
diff --git a/Documentation/userspace-api/ipc.rst b/Documentation/userspace-api/ipc.rst
new file mode 100644
index 000000000000..14a5f0ce7230
--- /dev/null
+++ b/Documentation/userspace-api/ipc.rst
@@ -0,0 +1,222 @@
+mq_timedreceive2 system call
+=============================
+
+This document describes the mq_timedreceive2() system call. It provides
+an overview of the feature, interface specification, design, and
+test specification.
+
+Contents
+--------
+
+ 1) Overview
+ 2) Functional Specification
+ 3) Design
+ 4) Implementation Notes
+ 5) Test Specification
+
+1) Overview
+-----------
+
+POSIX message queues on Linux provide mq_timedreceive() for consuming
+messages from a queue.This interface requires 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.
+
+One 64-bit variant is provided with compat handling:
+ mq_timedreceive2()
+
+2) 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 non-empty.
+
+ 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.
+
+3) Design
+---------
+
+3.1 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. Due to limited 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.
+
+3.2 Compat handling
+~~~~~~~~~~~~~~~~~~~~
+
+.. 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.
+
+3.3 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.
+
+3.4 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.
+
+4) Implementation Notes
+-----------------------
+
+The implementation lives in ipc/mqueue.c. The syscall entry
+point mq_timedreceive2 are thin wrappers that validate and convert
+arguments before calling the shared internal function do_mq_timedreceive2().
+
+Syscall numbers are assigned for all of most common architectures. Refer
+to the respective syscall table files under arch/ for per-architecture
+numbers.
+
+5) 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.
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..1a8b27127ca8 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__
@@ -9,10 +11,15 @@ ifeq ($(ARCH),x86_64)
ARCH := x86
CFLAGS := -DCONFIG_X86_64 -D__x86_64__
endif
+ifeq ($(ARCH),aarch64)
+ ARCH := arm64
+ CFLAGS := -DCONFIG_ARM64
+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..d08596ae6e1c
--- /dev/null
+++ b/tools/testing/selftests/ipc/mq_peek.c
@@ -0,0 +1,785 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* - Correct priority-rank indexed access (index 0 = highest priority)
+ * - FIFO ordering within same priority level
+ * - Concurrent peek + receive / peek + send races
+ */
+
+#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 <time.h>
+#include "mqueue.h"
+#include "kselftest.h"
+#include "linux/types.h"
+
+#ifndef __NR_mq_timedreceive2
+
+#if defined(__alpha__)
+#define __NR_mq_timedreceive2 582
+
+#elif defined(__x86_64__)
+#define __NR_mq_timedreceive2 548
+
+#else
+/* common value used by many architectures:
+ * arm m68k, microblaze, mips
+ * parisc, x86_32, and others
+ */
+#define __NR_mq_timedreceive2 472
+
+#endif
+#endif
+
+#define MQ_PEEK 2U
+
+#ifndef ARRAY_SIZE
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+#endif
+
+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) {
+ char rbuf[MAX_MSG_SIZE];
+ unsigned int rprio;
+
+ 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 = ARRAY_SIZE(prios);
+ 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(ARRAY_SIZE(tests));
+
+ {
+ 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
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