Add kernel API specification for the epoll_pwait() system call.
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
fs/eventpoll.c | 230 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 230 insertions(+)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 254b50d687d37..8bd25f9230fc8 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -3148,6 +3148,236 @@ static int do_epoll_pwait(int epfd, struct epoll_event
__user *events,
return error;
}
+
+DEFINE_KERNEL_API_SPEC(sys_epoll_pwait)
+ KAPI_DESCRIPTION("Wait for events on an epoll instance with signal
handling")
+ KAPI_LONG_DESC("Similar to epoll_wait(), but allows the caller to
safely wait for "
+ "either events on the epoll instance or the delivery of
a signal. "
+ "The sigmask argument specifies a signal mask which is
atomically "
+ "set during the wait, allowing signals to be blocked
while not waiting "
+ "and ensuring no signal is lost between checking for
events and blocking.")
+ KAPI_CONTEXT(KAPI_CTX_PROCESS | KAPI_CTX_SLEEPABLE)
+
+ KAPI_PARAM(0, "epfd", "int", "File descriptor referring to the epoll
instance")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_IN)
+ .type = KAPI_TYPE_FD,
+ .constraint_type = KAPI_CONSTRAINT_NONE,
+ KAPI_PARAM_END
+
+ KAPI_PARAM(1, "events", "struct epoll_event __user *", "Buffer where
ready events will be stored")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_OUT | KAPI_PARAM_USER)
+ .type = KAPI_TYPE_USER_PTR,
+ KAPI_PARAM_SIZE(sizeof(struct epoll_event))
+ .size_param_idx = 2, /* Size determined by maxevents parameter
*/
+ .size_multiplier = sizeof(struct epoll_event),
+ .constraint_type = KAPI_CONSTRAINT_NONE,
+ .constraints = "Must point to an array of at least maxevents
epoll_event structures",
+ KAPI_PARAM_END
+
+ KAPI_PARAM(2, "maxevents", "int", "Maximum number of events to return")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_IN)
+ .type = KAPI_TYPE_INT,
+ KAPI_PARAM_RANGE(1, INT_MAX / sizeof(struct epoll_event)) /*
EP_MAX_EVENTS */
+ .constraint_type = KAPI_CONSTRAINT_RANGE,
+ .constraints = "Must be greater than zero and not exceed system
limits",
+ KAPI_PARAM_END
+
+ KAPI_PARAM(3, "timeout", "int", "Timeout in milliseconds")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_IN)
+ .type = KAPI_TYPE_INT,
+ .constraint_type = KAPI_CONSTRAINT_NONE,
+ .constraints = "-1 blocks indefinitely, 0 returns immediately,
>0 specifies milliseconds to wait",
+ KAPI_PARAM_END
+
+ KAPI_PARAM(4, "sigmask", "const sigset_t __user *", "Signal mask to
atomically set during wait")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_IN | KAPI_PARAM_USER |
KAPI_PARAM_OPTIONAL)
+ .type = KAPI_TYPE_USER_PTR,
+ KAPI_PARAM_SIZE(sizeof(sigset_t))
+ .constraint_type = KAPI_CONSTRAINT_NONE,
+ .constraints = "Can be NULL if no signal mask change is
desired",
+ KAPI_PARAM_END
+
+ KAPI_PARAM(5, "sigsetsize", "size_t", "Size of the signal set in bytes")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_IN)
+ .type = KAPI_TYPE_UINT,
+ KAPI_PARAM_RANGE(sizeof(sigset_t), sizeof(sigset_t))
+ .constraint_type = KAPI_CONSTRAINT_RANGE,
+ .constraints = "Must be sizeof(sigset_t)",
+ KAPI_PARAM_END
+
+ KAPI_RETURN("long", "Number of ready file descriptors on success,
negative error code on failure")
+ .type = KAPI_TYPE_INT,
+ .check_type = KAPI_RETURN_RANGE,
+ .success_min = 0,
+ .success_max = INT_MAX,
+ KAPI_RETURN_END
+
+ KAPI_ERROR(0, -EBADF, "EBADF", "epfd is not a valid file descriptor",
+ "The epoll file descriptor is invalid or has been closed.")
+ KAPI_ERROR(1, -EFAULT, "EFAULT", "Memory area not accessible",
+ "The memory area pointed to by events or sigmask is not
accessible.")
+ KAPI_ERROR(2, -EINTR, "EINTR", "Call interrupted by signal handler",
+ "The call was interrupted by a signal handler before any
events "
+ "became ready or the timeout expired; see signal(7).")
+ KAPI_ERROR(3, -EINVAL, "EINVAL", "Invalid parameters",
+ "epfd is not an epoll file descriptor, maxevents is less
than or equal to zero, "
+ "or sigsetsize is not equal to sizeof(sigset_t).")
+
+ .error_count = 4,
+ .param_count = 6,
+ .since_version = "2.6.19",
+
+ /* Side effects */
+ KAPI_SIDE_EFFECT(0, KAPI_EFFECT_MODIFY_STATE,
+ "signal mask",
+ "Atomically sets the signal mask for the calling
thread")
+ KAPI_EFFECT_CONDITION("When sigmask is not NULL")
+ KAPI_EFFECT_REVERSIBLE
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT(1, KAPI_EFFECT_MODIFY_STATE,
+ "ready list",
+ "Removes events from the epoll ready list as they are
reported")
+ KAPI_EFFECT_CONDITION("When events are available and
level-triggered")
+ KAPI_EFFECT_REVERSIBLE
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT(2, KAPI_EFFECT_SCHEDULE,
+ "process state",
+ "Blocks the calling thread until events are available,
timeout, or signal")
+ KAPI_EFFECT_CONDITION("When timeout != 0 and no events are
immediately available")
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT(3, KAPI_EFFECT_MODIFY_STATE,
+ "user memory",
+ "Writes event data to user-provided buffer")
+ KAPI_EFFECT_CONDITION("When events are available")
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT(4, KAPI_EFFECT_PROCESS_STATE,
+ "saved signal mask",
+ "Saves and restores the original signal mask")
+ KAPI_EFFECT_CONDITION("When sigmask is not NULL")
+ KAPI_EFFECT_REVERSIBLE
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT_COUNT(5)
+
+ /* State transitions */
+ KAPI_STATE_TRANS(0, "signal mask", "original mask", "user-specified
mask",
+ "Thread's signal mask is atomically changed to the
provided mask")
+ KAPI_STATE_TRANS_COND("When sigmask is not NULL")
+ KAPI_STATE_TRANS_END
+
+ KAPI_STATE_TRANS(1, "process", "running", "blocked",
+ "Process blocks waiting for events with specified
signal mask")
+ KAPI_STATE_TRANS_COND("When no events available and timeout !=
0")
+ KAPI_STATE_TRANS_END
+
+ KAPI_STATE_TRANS(2, "process", "blocked", "running",
+ "Process wakes up due to events, timeout, or unblocked
signal")
+ KAPI_STATE_TRANS_COND("When wait condition is satisfied")
+ KAPI_STATE_TRANS_END
+
+ KAPI_STATE_TRANS(3, "signal mask", "user-specified mask", "original
mask",
+ "Thread's signal mask is restored to its original
value")
+ KAPI_STATE_TRANS_COND("When returning from epoll_pwait")
+ KAPI_STATE_TRANS_END
+
+ KAPI_STATE_TRANS(4, "pending signals", "blocked", "deliverable",
+ "Signals that were blocked by the temporary mask
become deliverable")
+ KAPI_STATE_TRANS_COND("When signal mask is restored and signals
were pending")
+ KAPI_STATE_TRANS_END
+
+ KAPI_STATE_TRANS_COUNT(5)
+
+ /* Signal specifications */
+ KAPI_SIGNAL(0, 0, "ANY_UNBLOCKED", KAPI_SIGNAL_RECEIVE,
KAPI_SIGNAL_ACTION_RETURN)
+ KAPI_SIGNAL_CONDITION("Signal not blocked by provided sigmask")
+ KAPI_SIGNAL_DESC("Any signal not blocked by the sigmask
parameter will interrupt "
+ "epoll_pwait() and cause it to return -EINTR.
The signal mask is "
+ "atomically set via set_user_sigmask() and
restored via "
+ "restore_saved_sigmask_unless() before
returning.")
+ KAPI_SIGNAL_RESTARTABLE
+ KAPI_SIGNAL_END
+
+ KAPI_SIGNAL(1, SIGKILL, "SIGKILL", KAPI_SIGNAL_RECEIVE,
KAPI_SIGNAL_ACTION_TERMINATE)
+ KAPI_SIGNAL_CONDITION("Cannot be blocked by sigmask")
+ KAPI_SIGNAL_DESC("SIGKILL cannot be blocked and will terminate
the process immediately. "
+ "The epoll_pwait call will not return.")
+ KAPI_SIGNAL_END
+
+ KAPI_SIGNAL(2, SIGSTOP, "SIGSTOP", KAPI_SIGNAL_RECEIVE,
KAPI_SIGNAL_ACTION_STOP)
+ KAPI_SIGNAL_CONDITION("Cannot be blocked by sigmask")
+ KAPI_SIGNAL_DESC("SIGSTOP cannot be blocked and will stop the
process. When continued "
+ "with SIGCONT, epoll_pwait may return -EINTR.")
+ KAPI_SIGNAL_END
+
+ KAPI_SIGNAL(3, 0, "BLOCKED_SIGNALS", KAPI_SIGNAL_BLOCK,
KAPI_SIGNAL_ACTION_DEFAULT)
+ KAPI_SIGNAL_CONDITION("Signals in provided sigmask")
+ KAPI_SIGNAL_DESC("Signals specified in the sigmask parameter
are blocked for the "
+ "duration of the epoll_pwait call. They remain
pending and will be "
+ "delivered after the signal mask is restored.")
+ KAPI_SIGNAL_END
+
+ KAPI_SIGNAL(4, SIGCONT, "SIGCONT", KAPI_SIGNAL_RECEIVE,
KAPI_SIGNAL_ACTION_CONTINUE)
+ KAPI_SIGNAL_CONDITION("When process is stopped")
+ KAPI_SIGNAL_DESC("SIGCONT resumes a stopped process. If
epoll_pwait was interrupted "
+ "by SIGSTOP, it may return -EINTR when
continued.")
+ KAPI_SIGNAL_END
+
+ .signal_count = 5,
+
+ /* Signal mask specifications */
+ KAPI_SIGNAL_MASK(0, "user_sigmask", "User-provided signal mask
atomically applied")
+ .description = "The signal mask provided in the sigmask
parameter is atomically "
+ "set for the duration of the wait operation.
This prevents race "
+ "conditions between checking for events and
blocking. The original "
+ "signal mask is restored before epoll_pwait
returns, unless the "
+ "return value is -EINTR (in which case the mask
is restored by "
+ "the signal delivery mechanism)."
+ KAPI_SIGNAL_MASK_END
+
+ .signal_mask_count = 1,
+
+ /* Locking specifications */
+ KAPI_LOCK(0, "ep->lock", KAPI_LOCK_SPINLOCK)
+ KAPI_LOCK_ACQUIRED
+ KAPI_LOCK_RELEASED
+ KAPI_LOCK_DESC("Protects the ready list while checking for and
consuming events")
+ KAPI_LOCK_END
+
+ KAPI_LOCK(1, "ep->mtx", KAPI_LOCK_MUTEX)
+ KAPI_LOCK_ACQUIRED
+ KAPI_LOCK_RELEASED
+ KAPI_LOCK_DESC("Protects against concurrent epoll_ctl
operations during wait")
+ KAPI_LOCK_END
+
+ .lock_count = 2,
+
+ .examples = "sigset_t sigmask;\n"
+ "struct epoll_event events[10];\n\n"
+ "/* Block SIGINT during epoll_pwait */\n"
+ "sigemptyset(&sigmask);\n"
+ "sigaddset(&sigmask, SIGINT);\n\n"
+ "int nfds = epoll_pwait(epfd, events, 10, 1000, &sigmask,
sizeof(sigmask));\n"
+ "if (nfds == -1) {\n"
+ " if (errno == EINTR) {\n"
+ " /* Handle signal */\n"
+ " }\n"
+ " perror(\"epoll_pwait\");\n"
+ " exit(EXIT_FAILURE);\n"
+ "}",
+ .notes = "epoll_pwait() is equivalent to atomically executing:\n"
+ " sigset_t origmask;\n"
+ " pthread_sigmask(SIG_SETMASK, &sigmask, &origmask);\n"
+ " ready = epoll_wait(epfd, events, maxevents, timeout);\n"
+ " pthread_sigmask(SIG_SETMASK, &origmask, NULL);\n"
+ "This atomicity prevents race conditions where a signal could
be delivered "
+ "after checking for events but before blocking in
epoll_wait(). "
+ "The signal mask is always restored before epoll_pwait()
returns.",
+KAPI_END_SPEC;
+
SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
int, maxevents, int, timeout, const sigset_t __user *, sigmask,
size_t, sigsetsize)
--
2.39.5
