//
// Cforall Version 1.0.0 Copyright (C) 2020 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// io.cfa --
//
// Author           : Thierry Delisle
// Created On       : Thu Apr 23 17:31:00 2020
// Last Modified By :
// Last Modified On :
// Update Count     :
//

#define __cforall_thread__

#if defined(__CFA_DEBUG__)
	// #define __CFA_DEBUG_PRINT_IO__
	// #define __CFA_DEBUG_PRINT_IO_CORE__
#endif


#if defined(CFA_HAVE_LINUX_IO_URING_H)
	#define _GNU_SOURCE         /* See feature_test_macros(7) */
	#include <errno.h>
	#include <signal.h>
	#include <stdint.h>
	#include <string.h>
	#include <unistd.h>

	extern "C" {
		#include <sys/epoll.h>
		#include <sys/syscall.h>

		#include <linux/io_uring.h>
	}

	#include "stats.hfa"
	#include "kernel.hfa"
	#include "kernel/fwd.hfa"
	#include "io/types.hfa"

	// returns true of acquired as leader or second leader
	static inline bool try_lock( __leaderlock_t & this ) {
		const uintptr_t thrd = 1z | (uintptr_t)active_thread();
		bool block;
		disable_interrupts();
		for() {
			struct $thread * expected = this.value;
			if( 1p != expected && 0p != expected ) {
				/* paranoid */ verify( thrd != (uintptr_t)expected ); // We better not already be the next leader
				enable_interrupts( __cfaabi_dbg_ctx );
				return false;
			}
			struct $thread * desired;
			if( 0p == expected ) {
				// If the lock isn't locked acquire it, no need to block
				desired = 1p;
				block = false;
			}
			else {
				// If the lock is already locked try becomming the next leader
				desired = (struct $thread *)thrd;
				block = true;
			}
			if( __atomic_compare_exchange_n(&this.value, &expected, desired, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ) break;
		}
		if( block ) {
			enable_interrupts( __cfaabi_dbg_ctx );
			park();
			disable_interrupts();
		}
		return true;
	}

	static inline bool next( __leaderlock_t & this ) {
		/* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
		struct $thread * nextt;
		for() {
			struct $thread * expected = this.value;
			/* paranoid */ verify( (1 & (uintptr_t)expected) == 1 ); // The lock better be locked

			struct $thread * desired;
			if( 1p == expected ) {
				// No next leader, just unlock
				desired = 0p;
				nextt   = 0p;
			}
			else {
				// There is a next leader, remove but keep locked
				desired = 1p;
				nextt   = (struct $thread *)(~1z & (uintptr_t)expected);
			}
			if( __atomic_compare_exchange_n(&this.value, &expected, desired, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ) break;
		}

		if(nextt) {
			unpark( nextt );
			enable_interrupts( __cfaabi_dbg_ctx );
			return true;
		}
		enable_interrupts( __cfaabi_dbg_ctx );
		return false;
	}

//=============================================================================================
// I/O Syscall
//=============================================================================================
	static int __io_uring_enter( struct __io_data & ring, unsigned to_submit, bool get ) {
		bool need_sys_to_submit = false;
		bool need_sys_to_complete = false;
		unsigned flags = 0;

		TO_SUBMIT:
		if( to_submit > 0 ) {
			if( !(ring.ring_flags & IORING_SETUP_SQPOLL) ) {
				need_sys_to_submit = true;
				break TO_SUBMIT;
			}
			if( (*ring.submit_q.flags) & IORING_SQ_NEED_WAKEUP ) {
				need_sys_to_submit = true;
				flags |= IORING_ENTER_SQ_WAKEUP;
			}
		}

		if( get && !(ring.ring_flags & IORING_SETUP_SQPOLL) ) {
			flags |= IORING_ENTER_GETEVENTS;
			if( (ring.ring_flags & IORING_SETUP_IOPOLL) ) {
				need_sys_to_complete = true;
			}
		}

		int ret = 0;
		if( need_sys_to_submit || need_sys_to_complete ) {
			ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, 0, flags, (sigset_t *)0p, _NSIG / 8);
			if( ret < 0 ) {
				switch((int)errno) {
				case EAGAIN:
				case EINTR:
					ret = -1;
					break;
				default:
					abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
				}
			}
		}

		// Memory barrier
		__atomic_thread_fence( __ATOMIC_SEQ_CST );
		return ret;
	}

//=============================================================================================
// I/O Polling
//=============================================================================================
	static unsigned __collect_submitions( struct __io_data & ring );
	static __u32 __release_consumed_submission( struct __io_data & ring );

	static inline void process(struct io_uring_cqe & cqe ) {
		struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
		__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", future, cqe.res, data->thrd );

		fulfil( *future, cqe.res );
	}

	// Process a single completion message from the io_uring
	// This is NOT thread-safe
	static [int, bool] __drain_io( & struct __io_data ring ) {
		/* paranoid */ verify( !kernelTLS.preemption_state.enabled );

		unsigned to_submit = 0;
		if( ring.poller_submits ) {
			// If the poller thread also submits, then we need to aggregate the submissions which are ready
			to_submit = __collect_submitions( ring );
		}

		int ret = __io_uring_enter(ring, to_submit, true);
		if( ret < 0 ) {
			return [0, true];
		}

		// update statistics
		if (to_submit > 0) {
			__STATS__( true,
				if( to_submit > 0 ) {
					io.submit_q.submit_avg.rdy += to_submit;
					io.submit_q.submit_avg.csm += ret;
					io.submit_q.submit_avg.cnt += 1;
				}
			)
		}

		// Release the consumed SQEs
		__release_consumed_submission( ring );

		// Drain the queue
		unsigned head = *ring.completion_q.head;
		unsigned tail = *ring.completion_q.tail;
		const __u32 mask = *ring.completion_q.mask;

		// Nothing was new return 0
		if (head == tail) {
			return [0, to_submit > 0];
		}

		__u32 count = tail - head;
		/* paranoid */ verify( count != 0 );
		for(i; count) {
			unsigned idx = (head + i) & mask;
			struct io_uring_cqe & cqe = ring.completion_q.cqes[idx];

			/* paranoid */ verify(&cqe);

			process( cqe );
		}

		// Mark to the kernel that the cqe has been seen
		// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
		__atomic_thread_fence( __ATOMIC_SEQ_CST );
		__atomic_fetch_add( ring.completion_q.head, count, __ATOMIC_RELAXED );

		return [count, count > 0 || to_submit > 0];
	}

	void main( $io_ctx_thread & this ) {
		epoll_event ev;
		__ioctx_register( this, ev );

		__cfadbg_print_safe(io_core, "Kernel I/O : IO poller %p for ring %p ready\n", &this, &this.ring);

		int reset = 0;
		// Then loop until we need to start
		while(!__atomic_load_n(&this.done, __ATOMIC_SEQ_CST)) {
			// Drain the io
			int count;
			bool again;
			disable_interrupts();
				[count, again] = __drain_io( *this.ring );

				if(!again) reset++;

				// Update statistics
				__STATS__( true,
					io.complete_q.completed_avg.val += count;
					io.complete_q.completed_avg.cnt += 1;
				)
			enable_interrupts( __cfaabi_dbg_ctx );

			// If we got something, just yield and check again
			if(reset < 5) {
				yield();
			}
			// We didn't get anything baton pass to the slow poller
			else {
				__STATS__( false,
					io.complete_q.blocks += 1;
				)
				__cfadbg_print_safe(io_core, "Kernel I/O : Parking io poller %p\n", &this.self);
				reset = 0;

				// block this thread
				__ioctx_prepare_block( this, ev );
				wait( this.sem );
			}
		}

		__cfadbg_print_safe(io_core, "Kernel I/O : Fast poller for ring %p stopping\n", &this.ring);
	}

//=============================================================================================
// I/O Submissions
//=============================================================================================

// Submition steps :
// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
//     listed in sq.array are visible by the kernel. For those not listed, the kernel does not
//     offer any assurance that an entry is not being filled by multiple flags. Therefore, we
//     need to write an allocator that allows allocating concurrently.
//
// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
//
// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
//     needs to arrive to two concensus at the same time:
//     A - The order in which entries are listed in the array: no two threads must pick the
//         same index for their entries
//     B - When can the tail be update for the kernel. EVERY entries in the array between
//         head and tail must be fully filled and shouldn't ever be touched again.
//

	[* struct io_uring_sqe, __u32] __submit_alloc( struct __io_data & ring, __u64 data ) {
		/* paranoid */ verify( data != 0 );

		// Prepare the data we need
		__attribute((unused)) int len   = 0;
		__attribute((unused)) int block = 0;
		__u32 cnt = *ring.submit_q.num;
		__u32 mask = *ring.submit_q.mask;

		disable_interrupts();
			__u32 off = __tls_rand();
		enable_interrupts( __cfaabi_dbg_ctx );

		// Loop around looking for an available spot
		for() {
			// Look through the list starting at some offset
			for(i; cnt) {
				__u64 expected = 0;
				__u32 idx = (i + off) & mask;
				struct io_uring_sqe * sqe = &ring.submit_q.sqes[idx];
				volatile __u64 * udata = &sqe->user_data;

				if( *udata == expected &&
					__atomic_compare_exchange_n( udata, &expected, data, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) )
				{
					// update statistics
					__STATS__( false,
						io.submit_q.alloc_avg.val   += len;
						io.submit_q.alloc_avg.block += block;
						io.submit_q.alloc_avg.cnt   += 1;
					)


					// Success return the data
					return [sqe, idx];
				}
				verify(expected != data);

				len ++;
			}

			block++;
			yield();
		}
	}

	static inline __u32 __submit_to_ready_array( struct __io_data & ring, __u32 idx, const __u32 mask ) {
		/* paranoid */ verify( idx <= mask   );
		/* paranoid */ verify( idx != -1ul32 );

		// We need to find a spot in the ready array
		__attribute((unused)) int len   = 0;
		__attribute((unused)) int block = 0;
		__u32 ready_mask = ring.submit_q.ready_cnt - 1;

		disable_interrupts();
			__u32 off = __tls_rand();
		enable_interrupts( __cfaabi_dbg_ctx );

		__u32 picked;
		LOOKING: for() {
			for(i; ring.submit_q.ready_cnt) {
				picked = (i + off) & ready_mask;
				__u32 expected = -1ul32;
				if( __atomic_compare_exchange_n( &ring.submit_q.ready[picked], &expected, idx, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) ) {
					break LOOKING;
				}
				verify(expected != idx);

				len ++;
			}

			block++;

			__u32 released = __release_consumed_submission( ring );
			if( released == 0 ) {
				yield();
			}
		}

		// update statistics
		__STATS__( false,
			io.submit_q.look_avg.val   += len;
			io.submit_q.look_avg.block += block;
			io.submit_q.look_avg.cnt   += 1;
		)

		return picked;
	}

	void __submit( struct io_context * ctx, __u32 idx ) __attribute__((nonnull (1))) {
		__io_data & ring = *ctx->thrd.ring;
		// Get now the data we definetely need
		volatile __u32 * const tail = ring.submit_q.tail;
		const __u32 mask  = *ring.submit_q.mask;

		// There are 2 submission schemes, check which one we are using
		if( ring.poller_submits ) {
			// If the poller thread submits, then we just need to add this to the ready array
			__submit_to_ready_array( ring, idx, mask );

			post( ctx->thrd.sem );

			__cfadbg_print_safe( io, "Kernel I/O : Added %u to ready for %p\n", idx, active_thread() );
		}
		else if( ring.eager_submits ) {
			__u32 picked = __submit_to_ready_array( ring, idx, mask );

			#if defined(LEADER_LOCK)
				if( !try_lock(ring.submit_q.submit_lock) ) {
					__STATS__( false,
						io.submit_q.helped += 1;
					)
					return;
				}
				/* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
				__STATS__( true,
					io.submit_q.leader += 1;
				)
			#else
				for() {
					yield();

					if( try_lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2) ) {
						__STATS__( false,
							io.submit_q.leader += 1;
						)
						break;
					}

					// If some one else collected our index, we are done
					#warning ABA problem
					if( ring.submit_q.ready[picked] != idx ) {
						__STATS__( false,
							io.submit_q.helped += 1;
						)
						return;
					}

					__STATS__( false,
						io.submit_q.busy += 1;
					)
				}
			#endif

			// We got the lock
			// Collect the submissions
			unsigned to_submit = __collect_submitions( ring );

			// Actually submit
			int ret = __io_uring_enter( ring, to_submit, false );

			#if defined(LEADER_LOCK)
				/* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
				next(ring.submit_q.submit_lock);
			#else
				unlock(ring.submit_q.submit_lock);
			#endif
			if( ret < 0 ) return;

			// Release the consumed SQEs
			__release_consumed_submission( ring );

			// update statistics
			__STATS__( false,
				io.submit_q.submit_avg.rdy += to_submit;
				io.submit_q.submit_avg.csm += ret;
				io.submit_q.submit_avg.cnt += 1;
			)
		}
		else {
			// get mutual exclusion
			#if defined(LEADER_LOCK)
				while(!try_lock(ring.submit_q.submit_lock));
			#else
				lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2);
			#endif

			/* paranoid */ verifyf( ring.submit_q.sqes[ idx ].user_data != 0,
			/* paranoid */ 	"index %u already reclaimed\n"
			/* paranoid */ 	"head %u, prev %u, tail %u\n"
			/* paranoid */ 	"[-0: %u,-1: %u,-2: %u,-3: %u]\n",
			/* paranoid */ 	idx,
			/* paranoid */ 	*ring.submit_q.head, ring.submit_q.prev_head, *tail
			/* paranoid */ 	,ring.submit_q.array[ ((*ring.submit_q.head) - 0) & (*ring.submit_q.mask) ]
			/* paranoid */ 	,ring.submit_q.array[ ((*ring.submit_q.head) - 1) & (*ring.submit_q.mask) ]
			/* paranoid */ 	,ring.submit_q.array[ ((*ring.submit_q.head) - 2) & (*ring.submit_q.mask) ]
			/* paranoid */ 	,ring.submit_q.array[ ((*ring.submit_q.head) - 3) & (*ring.submit_q.mask) ]
			/* paranoid */ );

			// Append to the list of ready entries

			/* paranoid */ verify( idx <= mask );
			ring.submit_q.array[ (*tail) & mask ] = idx;
			__atomic_fetch_add(tail, 1ul32, __ATOMIC_SEQ_CST);

			// Submit however, many entries need to be submitted
			int ret = __io_uring_enter( ring, 1, false );
			if( ret < 0 ) {
				switch((int)errno) {
				default:
					abort( "KERNEL ERROR: IO_URING SUBMIT - %s\n", strerror(errno) );
				}
			}

			// update statistics
			__STATS__( false,
				io.submit_q.submit_avg.csm += 1;
				io.submit_q.submit_avg.cnt += 1;
			)

			// Release the consumed SQEs
			__release_consumed_submission( ring );

			#if defined(LEADER_LOCK)
				next(ring.submit_q.submit_lock);
			#else
				unlock(ring.submit_q.submit_lock);
			#endif

			__cfadbg_print_safe( io, "Kernel I/O : Performed io_submit for %p, returned %d\n", active_thread(), ret );
		}
	}

	// #define PARTIAL_SUBMIT 32
	static unsigned __collect_submitions( struct __io_data & ring ) {
		/* paranoid */ verify( ring.submit_q.ready != 0p );
		/* paranoid */ verify( ring.submit_q.ready_cnt > 0 );

		unsigned to_submit = 0;
		__u32 tail = *ring.submit_q.tail;
		const __u32 mask = *ring.submit_q.mask;
		#if defined(PARTIAL_SUBMIT)
			#if defined(LEADER_LOCK)
				#error PARTIAL_SUBMIT and LEADER_LOCK cannot co-exist
			#endif
			const __u32 cnt = ring.submit_q.ready_cnt > PARTIAL_SUBMIT ? PARTIAL_SUBMIT : ring.submit_q.ready_cnt;
			const __u32 offset = ring.submit_q.prev_ready;
			ring.submit_q.prev_ready += cnt;
		#else
			const __u32 cnt = ring.submit_q.ready_cnt;
			const __u32 offset = 0;
		#endif

		// Go through the list of ready submissions
		for( c; cnt ) {
			__u32 i = (offset + c) % ring.submit_q.ready_cnt;

			// replace any submission with the sentinel, to consume it.
			__u32 idx = __atomic_exchange_n( &ring.submit_q.ready[i], -1ul32, __ATOMIC_RELAXED);

			// If it was already the sentinel, then we are done
			if( idx == -1ul32 ) continue;

			// If we got a real submission, append it to the list
			ring.submit_q.array[ (tail + to_submit) & mask ] = idx & mask;
			to_submit++;
		}

		// Increment the tail based on how many we are ready to submit
		__atomic_fetch_add(ring.submit_q.tail, to_submit, __ATOMIC_SEQ_CST);

		return to_submit;
	}

	static __u32 __release_consumed_submission( struct __io_data & ring ) {
		const __u32 smask = *ring.submit_q.mask;

		if( !try_lock(ring.submit_q.release_lock __cfaabi_dbg_ctx2) ) return 0;
		__u32 chead = *ring.submit_q.head;
		__u32 phead = ring.submit_q.prev_head;
		ring.submit_q.prev_head = chead;
		unlock(ring.submit_q.release_lock);

		__u32 count = chead - phead;
		for( i; count ) {
			__u32 idx = ring.submit_q.array[ (phead + i) & smask ];
			ring.submit_q.sqes[ idx ].user_data = 0;
		}
		return count;
	}
#endif