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ADT ast-experimental enum forall-pointer-decay pthread-emulation qualifiedEnum

Last change on this file since 3cc1111 was 2514f68b, checked in by Thierry Delisle <tdelisle@…>, 4 years ago
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File size: 16.3 KB

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[ecf6b46]	1	//
	2	// Cforall Version 1.0.0 Copyright (C) 2020 University of Waterloo
	3	//
	4	// The contents of this file are covered under the licence agreement in the
	5	// file "LICENCE" distributed with Cforall.
	6	//
	7	// io.cfa --
	8	//
	9	// Author : Thierry Delisle
	10	// Created On : Thu Apr 23 17:31:00 2020
	11	// Last Modified By :
	12	// Last Modified On :
	13	// Update Count :
	14	//
	15
[3e2b9c9]	16	#define __cforall_thread__
[43784ac]	17	#define _GNU_SOURCE
[3e2b9c9]	18
[20ab637]	19	#if defined(__CFA_DEBUG__)
[d60d30e]	20	// #define __CFA_DEBUG_PRINT_IO__
	21	// #define __CFA_DEBUG_PRINT_IO_CORE__
[20ab637]	22	#endif
[4069faad]	23
[f6660520]	24
[3e2b9c9]	25	#if defined(CFA_HAVE_LINUX_IO_URING_H)
[31bb2e1]	26	#include <errno.h>
[3e2b9c9]	27	#include <signal.h>
[31bb2e1]	28	#include <stdint.h>
	29	#include <string.h>
	30	#include <unistd.h>
	31
[92976d9]	32	extern "C" {
	33	#include <sys/syscall.h>
[dddb3dd0]	34	#include <sys/eventfd.h>
[92976d9]	35
	36	#include <linux/io_uring.h>
	37	}
	38
[3e2b9c9]	39	#include "stats.hfa"
	40	#include "kernel.hfa"
	41	#include "kernel/fwd.hfa"
[e9c0b4c]	42	#include "kernel_private.hfa"
[3e2b9c9]	43	#include "io/types.hfa"
[185efe6]	44
[2fab24e3]	45	__attribute__((unused)) static const char * opcodes[] = {
[426f60c]	46	"OP_NOP",
	47	"OP_READV",
	48	"OP_WRITEV",
	49	"OP_FSYNC",
	50	"OP_READ_FIXED",
	51	"OP_WRITE_FIXED",
	52	"OP_POLL_ADD",
	53	"OP_POLL_REMOVE",
	54	"OP_SYNC_FILE_RANGE",
	55	"OP_SENDMSG",
	56	"OP_RECVMSG",
	57	"OP_TIMEOUT",
	58	"OP_TIMEOUT_REMOVE",
	59	"OP_ACCEPT",
	60	"OP_ASYNC_CANCEL",
	61	"OP_LINK_TIMEOUT",
	62	"OP_CONNECT",
	63	"OP_FALLOCATE",
	64	"OP_OPENAT",
	65	"OP_CLOSE",
	66	"OP_FILES_UPDATE",
	67	"OP_STATX",
	68	"OP_READ",
	69	"OP_WRITE",
	70	"OP_FADVISE",
	71	"OP_MADVISE",
	72	"OP_SEND",
	73	"OP_RECV",
	74	"OP_OPENAT2",
	75	"OP_EPOLL_CTL",
	76	"OP_SPLICE",
	77	"OP_PROVIDE_BUFFERS",
	78	"OP_REMOVE_BUFFERS",
	79	"OP_TEE",
	80	"INVALID_OP"
	81	};
	82
[11054eb]	83	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want );
	84	static void __ioarbiter_submit( $io_context * , __u32 idxs[], __u32 have, bool lazy );
	85	static void __ioarbiter_flush ( $io_context & );
[dddb3dd0]	86	static inline void __ioarbiter_notify( $io_context & ctx );
[92976d9]	87	//=============================================================================================
	88	// I/O Polling
	89	//=============================================================================================
[78da4ab]	90	static inline unsigned __flush( struct $io_context & );
	91	static inline __u32 __release_sqes( struct $io_context & );
[24e321c]	92	extern void __kernel_unpark( thread$ * thrd, unpark_hint );
[1d5e4711]	93
[c1c95b1]	94	bool __cfa_io_drain( processor * proc ) {
[dddb3dd0]	95	/* paranoid */ verify( ! __preemption_enabled() );
[e9c0b4c]	96	/* paranoid */ verify( ready_schedule_islocked() );
[dddb3dd0]	97	/* paranoid */ verify( proc );
	98	/* paranoid */ verify( proc->io.ctx );
[6f121b8]	99
[d384787]	100	// Drain the queue
[dddb3dd0]	101	$io_context * ctx = proc->io.ctx;
	102	unsigned head = *ctx->cq.head;
	103	unsigned tail = *ctx->cq.tail;
	104	const __u32 mask = *ctx->cq.mask;
[92976d9]	105
[4998155]	106	__u32 count = tail - head;
[dddb3dd0]	107	__STATS__( false, io.calls.drain++; io.calls.completed += count; )
[d60d30e]	108
[c1c95b1]	109	if(count == 0) return false;
	110
[d384787]	111	for(i; count) {
[6f121b8]	112	unsigned idx = (head + i) & mask;
[dddb3dd0]	113	volatile struct io_uring_cqe & cqe = ctx->cq.cqes[idx];
[92976d9]	114
[d384787]	115	/* paranoid */ verify(&cqe);
[92976d9]	116
[78da4ab]	117	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
	118	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
	119
[24e321c]	120	__kernel_unpark( fulfil( *future, cqe.res, false ), UNPARK_LOCAL );
[78da4ab]	121	}
	122
[dddb3dd0]	123	__cfadbg_print_safe(io, "Kernel I/O : %u completed\n", count);
[2d8f7b0]	124
[92976d9]	125	// Mark to the kernel that the cqe has been seen
	126	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
[dddb3dd0]	127	__atomic_store_n( ctx->cq.head, head + count, __ATOMIC_SEQ_CST );
[92976d9]	128
[e9c0b4c]	129	/* paranoid */ verify( ready_schedule_islocked() );
[dddb3dd0]	130	/* paranoid */ verify( ! __preemption_enabled() );
	131
[c1c95b1]	132	return true;
[92976d9]	133	}
	134
[059ad16]	135	bool __cfa_io_flush( processor * proc, bool wait ) {
[dddb3dd0]	136	/* paranoid */ verify( ! __preemption_enabled() );
	137	/* paranoid */ verify( proc );
	138	/* paranoid */ verify( proc->io.ctx );
[1539bbd]	139
[d36bac7]	140	__attribute__((unused)) cluster * cltr = proc->cltr;
[dddb3dd0]	141	$io_context & ctx = *proc->io.ctx;
[78da4ab]	142
[11054eb]	143	__ioarbiter_flush( ctx );
[3c039b0]	144
[dddb3dd0]	145	__STATS__( true, io.calls.flush++; )
[059ad16]	146	int ret = syscall( __NR_io_uring_enter, ctx.fd, ctx.sq.to_submit, wait ? 1 : 0, 0, (sigset_t *)0p, _NSIG / 8);
[dddb3dd0]	147	if( ret < 0 ) {
	148	switch((int)errno) {
	149	case EAGAIN:
	150	case EINTR:
	151	case EBUSY:
	152	// Update statistics
	153	__STATS__( false, io.calls.errors.busy ++; )
[059ad16]	154	return false;
[dddb3dd0]	155	default:
	156	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
[61dd73d]	157	}
[dddb3dd0]	158	}
[ece0e80]	159
[dddb3dd0]	160	__cfadbg_print_safe(io, "Kernel I/O : %u submitted to io_uring %d\n", ret, ctx.fd);
	161	__STATS__( true, io.calls.submitted += ret; )
	162	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
	163	/* paranoid */ verify( ctx.sq.to_submit >= ret );
	164
	165	ctx.sq.to_submit -= ret;
[ece0e80]	166
[dddb3dd0]	167	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
[5dadc9b7]	168
[dddb3dd0]	169	// Release the consumed SQEs
	170	__release_sqes( ctx );
[ece0e80]	171
[dddb3dd0]	172	/* paranoid */ verify( ! __preemption_enabled() );
[61dd73d]	173
[dddb3dd0]	174	ctx.proc->io.pending = false;
[7ef162b2]	175	ready_schedule_lock();
	176	bool ret = __cfa_io_drain( proc );
	177	ready_schedule_unlock();
	178	return ret;
[61dd73d]	179	}
[f6660520]	180
[92976d9]	181	//=============================================================================================
	182	// I/O Submissions
	183	//=============================================================================================
	184
[2d8f7b0]	185	// Submition steps :
[e46c753]	186	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
[2d8f7b0]	187	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
	188	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
	189	// need to write an allocator that allows allocating concurrently.
	190	//
[e46c753]	191	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
[2d8f7b0]	192	//
[e46c753]	193	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
[2d8f7b0]	194	// needs to arrive to two concensus at the same time:
	195	// A - The order in which entries are listed in the array: no two threads must pick the
	196	// same index for their entries
	197	// B - When can the tail be update for the kernel. EVERY entries in the array between
	198	// head and tail must be fully filled and shouldn't ever be touched again.
	199	//
[78da4ab]	200	//=============================================================================================
	201	// Allocation
	202	// for user's convenience fill the sqes from the indexes
	203	static inline void __fill(struct io_uring_sqe * out_sqes[], __u32 want, __u32 idxs[], struct $io_context * ctx) {
	204	struct io_uring_sqe * sqes = ctx->sq.sqes;
	205	for(i; want) {
[dddb3dd0]	206	__cfadbg_print_safe(io, "Kernel I/O : filling loop\n");
[78da4ab]	207	out_sqes[i] = &sqes[idxs[i]];
	208	}
	209	}
[2489d31]	210
[78da4ab]	211	// Try to directly allocate from the a given context
	212	// Not thread-safe
	213	static inline bool __alloc(struct $io_context * ctx, __u32 idxs[], __u32 want) {
	214	__sub_ring_t & sq = ctx->sq;
	215	const __u32 mask = *sq.mask;
	216	__u32 fhead = sq.free_ring.head; // get the current head of the queue
	217	__u32 ftail = sq.free_ring.tail; // get the current tail of the queue
[2489d31]	218
[78da4ab]	219	// If we don't have enough sqes, fail
	220	if((ftail - fhead) < want) { return false; }
[426f60c]	221
[78da4ab]	222	// copy all the indexes we want from the available list
	223	for(i; want) {
[dddb3dd0]	224	__cfadbg_print_safe(io, "Kernel I/O : allocating loop\n");
[78da4ab]	225	idxs[i] = sq.free_ring.array[(fhead + i) & mask];
[6f121b8]	226	}
[2489d31]	227
[78da4ab]	228	// Advance the head to mark the indexes as consumed
	229	__atomic_store_n(&sq.free_ring.head, fhead + want, __ATOMIC_RELEASE);
[df40a56]	230
[78da4ab]	231	// return success
	232	return true;
	233	}
[df40a56]	234
[78da4ab]	235	// Allocate an submit queue entry.
	236	// The kernel cannot see these entries until they are submitted, but other threads must be
	237	// able to see which entries can be used and which are already un used by an other thread
	238	// for convenience, return both the index and the pointer to the sqe
	239	// sqe == &sqes[idx]
	240	struct $io_context * cfa_io_allocate(struct io_uring_sqe * sqes[], __u32 idxs[], __u32 want) {
	241	__cfadbg_print_safe(io, "Kernel I/O : attempting to allocate %u\n", want);
[df40a56]	242
[78da4ab]	243	disable_interrupts();
	244	processor * proc = __cfaabi_tls.this_processor;
[dddb3dd0]	245	$io_context * ctx = proc->io.ctx;
[78da4ab]	246	/* paranoid */ verify( __cfaabi_tls.this_processor );
[dddb3dd0]	247	/* paranoid */ verify( ctx );
[78da4ab]	248
[dddb3dd0]	249	__cfadbg_print_safe(io, "Kernel I/O : attempting to fast allocation\n");
[78da4ab]	250
[dddb3dd0]	251	// We can proceed to the fast path
	252	if( __alloc(ctx, idxs, want) ) {
	253	// Allocation was successful
	254	__STATS__( true, io.alloc.fast += 1; )
[a3821fa]	255	enable_interrupts();
[df40a56]	256
[dddb3dd0]	257	__cfadbg_print_safe(io, "Kernel I/O : fast allocation successful from ring %d\n", ctx->fd);
[2fafe7e]	258
[dddb3dd0]	259	__fill( sqes, want, idxs, ctx );
	260	return ctx;
[df40a56]	261	}
[dddb3dd0]	262	// The fast path failed, fallback
	263	__STATS__( true, io.alloc.fail += 1; )
[df40a56]	264
[78da4ab]	265	// Fast path failed, fallback on arbitration
[d60d30e]	266	__STATS__( true, io.alloc.slow += 1; )
[a3821fa]	267	enable_interrupts();
[78da4ab]	268
[dddb3dd0]	269	$io_arbiter * ioarb = proc->cltr->io.arbiter;
	270	/* paranoid */ verify( ioarb );
	271
[78da4ab]	272	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for allocation\n");
	273
[11054eb]	274	struct $io_context * ret = __ioarbiter_allocate(*ioarb, idxs, want);
[78da4ab]	275
[dddb3dd0]	276	__cfadbg_print_safe(io, "Kernel I/O : slow allocation completed from ring %d\n", ret->fd);
[df40a56]	277
[78da4ab]	278	__fill( sqes, want, idxs,ret );
	279	return ret;
[df40a56]	280	}
	281
[78da4ab]	282	//=============================================================================================
	283	// submission
[dddb3dd0]	284	static inline void __submit( struct $io_context * ctx, __u32 idxs[], __u32 have, bool lazy) {
[78da4ab]	285	// We can proceed to the fast path
	286	// Get the right objects
	287	__sub_ring_t & sq = ctx->sq;
	288	const __u32 mask = *sq.mask;
[dddb3dd0]	289	__u32 tail = *sq.kring.tail;
[78da4ab]	290
	291	// Add the sqes to the array
	292	for( i; have ) {
[dddb3dd0]	293	__cfadbg_print_safe(io, "Kernel I/O : __submit loop\n");
[78da4ab]	294	sq.kring.array[ (tail + i) & mask ] = idxs[i];
[426f60c]	295	}
	296
[78da4ab]	297	// Make the sqes visible to the submitter
[dddb3dd0]	298	__atomic_store_n(sq.kring.tail, tail + have, __ATOMIC_RELEASE);
[e8ac228]	299	sq.to_submit += have;
[426f60c]	300
[dddb3dd0]	301	ctx->proc->io.pending = true;
	302	ctx->proc->io.dirty = true;
	303	if(sq.to_submit > 30 \|\| !lazy) {
[059ad16]	304	__cfa_io_flush( ctx->proc, false );
[dddb3dd0]	305	}
[78da4ab]	306	}
[2489d31]	307
[dddb3dd0]	308	void cfa_io_submit( struct $io_context * inctx, __u32 idxs[], __u32 have, bool lazy ) __attribute__((nonnull (1))) {
	309	__cfadbg_print_safe(io, "Kernel I/O : attempting to submit %u (%s)\n", have, lazy ? "lazy" : "eager");
[5dadc9b7]	310
[78da4ab]	311	disable_interrupts();
	312	processor * proc = __cfaabi_tls.this_processor;
	313	$io_context * ctx = proc->io.ctx;
[dddb3dd0]	314	/* paranoid */ verify( __cfaabi_tls.this_processor );
	315	/* paranoid */ verify( ctx );
[e46c753]	316
[78da4ab]	317	// Can we proceed to the fast path
[dddb3dd0]	318	if( ctx == inctx ) // We have the right instance?
[78da4ab]	319	{
[dddb3dd0]	320	__submit(ctx, idxs, have, lazy);
[e46c753]	321
[78da4ab]	322	// Mark the instance as no longer in-use, re-enable interrupts and return
[d60d30e]	323	__STATS__( true, io.submit.fast += 1; )
[a3821fa]	324	enable_interrupts();
[ece0e80]	325
[78da4ab]	326	__cfadbg_print_safe(io, "Kernel I/O : submitted on fast path\n");
	327	return;
[e46c753]	328	}
[d384787]	329
[78da4ab]	330	// Fast path failed, fallback on arbitration
[d60d30e]	331	__STATS__( true, io.submit.slow += 1; )
[a3821fa]	332	enable_interrupts();
[5dadc9b7]	333
[78da4ab]	334	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for submission\n");
[426f60c]	335
[11054eb]	336	__ioarbiter_submit(inctx, idxs, have, lazy);
[78da4ab]	337	}
[2fab24e3]	338
[78da4ab]	339	//=============================================================================================
	340	// Flushing
[426f60c]	341	// Go through the ring's submit queue and release everything that has already been consumed
	342	// by io_uring
[78da4ab]	343	// This cannot be done by multiple threads
	344	static __u32 __release_sqes( struct $io_context & ctx ) {
	345	const __u32 mask = *ctx.sq.mask;
[732b406]	346
[426f60c]	347	__attribute__((unused))
[78da4ab]	348	__u32 ctail = *ctx.sq.kring.tail; // get the current tail of the queue
	349	__u32 chead = *ctx.sq.kring.head; // get the current head of the queue
	350	__u32 phead = ctx.sq.kring.released; // get the head the last time we were here
	351
	352	__u32 ftail = ctx.sq.free_ring.tail; // get the current tail of the queue
[732b406]	353
[426f60c]	354	// the 3 fields are organized like this diagram
	355	// except it's are ring
	356	// ---+--------+--------+----
	357	// ---+--------+--------+----
	358	// ^ ^ ^
	359	// phead chead ctail
	360
	361	// make sure ctail doesn't wrap around and reach phead
	362	/* paranoid */ verify(
	363	(ctail >= chead && chead >= phead)
	364	\|\| (chead >= phead && phead >= ctail)
	365	\|\| (phead >= ctail && ctail >= chead)
	366	);
	367
	368	// find the range we need to clear
[4998155]	369	__u32 count = chead - phead;
[426f60c]	370
[78da4ab]	371	if(count == 0) {
	372	return 0;
	373	}
	374
[426f60c]	375	// We acquired an previous-head/current-head range
	376	// go through the range and release the sqes
[34b61882]	377	for( i; count ) {
[dddb3dd0]	378	__cfadbg_print_safe(io, "Kernel I/O : release loop\n");
[78da4ab]	379	__u32 idx = ctx.sq.kring.array[ (phead + i) & mask ];
	380	ctx.sq.free_ring.array[ (ftail + i) & mask ] = idx;
[34b61882]	381	}
[78da4ab]	382
	383	ctx.sq.kring.released = chead; // note up to were we processed
	384	__atomic_store_n(&ctx.sq.free_ring.tail, ftail + count, __ATOMIC_SEQ_CST);
	385
	386	__ioarbiter_notify(ctx);
	387
[34b61882]	388	return count;
	389	}
[35285fd]	390
[78da4ab]	391	//=============================================================================================
	392	// I/O Arbiter
	393	//=============================================================================================
[11054eb]	394	static inline void block(__outstanding_io_queue & queue, __outstanding_io & item) {
	395	// Lock the list, it's not thread safe
	396	lock( queue.lock __cfaabi_dbg_ctx2 );
	397	{
	398	// Add our request to the list
	399	add( queue.queue, item );
	400
	401	// Mark as pending
	402	__atomic_store_n( &queue.empty, false, __ATOMIC_SEQ_CST );
	403	}
	404	unlock( queue.lock );
	405
	406	wait( item.sem );
	407	}
	408
	409	static inline bool empty(__outstanding_io_queue & queue ) {
	410	return __atomic_load_n( &queue.empty, __ATOMIC_SEQ_CST);
	411	}
	412
	413	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want ) {
[78da4ab]	414	__cfadbg_print_safe(io, "Kernel I/O : arbiter allocating\n");
	415
[d60d30e]	416	__STATS__( false, io.alloc.block += 1; )
	417
[78da4ab]	418	// No one has any resources left, wait for something to finish
[11054eb]	419	// We need to add ourself to a list of pending allocs and wait for an answer
	420	__pending_alloc pa;
	421	pa.idxs = idxs;
	422	pa.want = want;
[78da4ab]	423
[11054eb]	424	block(this.pending, (__outstanding_io&)pa);
[78da4ab]	425
[11054eb]	426	return pa.ctx;
[dddb3dd0]	427
[78da4ab]	428	}
	429
[11054eb]	430	static void __ioarbiter_notify( $io_arbiter & this, $io_context * ctx ) {
	431	/* paranoid */ verify( !empty(this.pending.queue) );
[78da4ab]	432
[11054eb]	433	lock( this.pending.lock __cfaabi_dbg_ctx2 );
	434	{
	435	while( !empty(this.pending.queue) ) {
	436	__cfadbg_print_safe(io, "Kernel I/O : notifying\n");
	437	__u32 have = ctx->sq.free_ring.tail - ctx->sq.free_ring.head;
	438	__pending_alloc & pa = (__pending_alloc&)head( this.pending.queue );
[78da4ab]	439
[11054eb]	440	if( have > pa.want ) goto DONE;
	441	drop( this.pending.queue );
[78da4ab]	442
[11054eb]	443	/* paranoid */__attribute__((unused)) bool ret =
[78da4ab]	444
[11054eb]	445	__alloc(ctx, pa.idxs, pa.want);
	446
	447	/* paranoid */ verify( ret );
	448
	449	pa.ctx = ctx;
	450
	451	post( pa.sem );
	452	}
	453
	454	this.pending.empty = true;
	455	DONE:;
	456	}
	457	unlock( this.pending.lock );
[78da4ab]	458	}
	459
	460	static void __ioarbiter_notify( $io_context & ctx ) {
[11054eb]	461	if(!empty( ctx.arbiter->pending )) {
[78da4ab]	462	__ioarbiter_notify( *ctx.arbiter, &ctx );
	463	}
	464	}
	465
	466	// Simply append to the pending
[11054eb]	467	static void __ioarbiter_submit( $io_context * ctx, __u32 idxs[], __u32 have, bool lazy ) {
[78da4ab]	468	__cfadbg_print_safe(io, "Kernel I/O : submitting %u from the arbiter to context %u\n", have, ctx->fd);
	469
	470	__cfadbg_print_safe(io, "Kernel I/O : waiting to submit %u\n", have);
	471
[11054eb]	472	__external_io ei;
	473	ei.idxs = idxs;
	474	ei.have = have;
	475	ei.lazy = lazy;
[78da4ab]	476
[11054eb]	477	block(ctx->ext_sq, (__outstanding_io&)ei);
[78da4ab]	478
	479	__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);
	480	}
	481
[11054eb]	482	static void __ioarbiter_flush( $io_context & ctx ) {
	483	if(!empty( ctx.ext_sq )) {
	484	__STATS__( false, io.flush.external += 1; )
[78da4ab]	485
[11054eb]	486	__cfadbg_print_safe(io, "Kernel I/O : arbiter flushing\n");
[d60d30e]	487
[11054eb]	488	lock( ctx.ext_sq.lock __cfaabi_dbg_ctx2 );
	489	{
	490	while( !empty(ctx.ext_sq.queue) ) {
	491	__external_io & ei = (__external_io&)drop( ctx.ext_sq.queue );
[78da4ab]	492
[11054eb]	493	__submit(&ctx, ei.idxs, ei.have, ei.lazy);
[78da4ab]	494
[11054eb]	495	post( ei.sem );
	496	}
	497
	498	ctx.ext_sq.empty = true;
	499	}
	500	unlock(ctx.ext_sq.lock );
	501	}
[78da4ab]	502	}
[7ef162b2]	503
[2514f68b]	504	#if defined(IO_URING_IDLE)
[6ddef36]	505	bool __kernel_read(processor * proc, io_future_t & future, char buf[], int fd) {
	506	$io_context * ctx = proc->io.ctx;
	507	/* paranoid */ verify( ! __preemption_enabled() );
	508	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
	509	/* paranoid */ verify( ctx );
[7ef162b2]	510
[6ddef36]	511	__u32 idx;
	512	struct io_uring_sqe * sqe;
[7ef162b2]	513
[6ddef36]	514	// We can proceed to the fast path
	515	if( !__alloc(ctx, &idx, 1) ) return false;
	516
	517	// Allocation was successful
	518	__fill( &sqe, 1, &idx, ctx );
	519
	520	sqe->opcode = IORING_OP_READ;
	521	sqe->user_data = (uintptr_t)&future;
	522	sqe->flags = 0;
	523	sqe->ioprio = 0;
	524	sqe->fd = 0;
	525	sqe->off = 0;
	526	sqe->fsync_flags = 0;
	527	sqe->__pad2[0] = 0;
	528	sqe->__pad2[1] = 0;
	529	sqe->__pad2[2] = 0;
	530	sqe->addr = (uintptr_t)buf;
	531	sqe->len = sizeof(uint64_t);
	532
	533	asm volatile("": : :"memory");
	534
	535	/* paranoid */ verify( sqe->user_data == (uintptr_t)&future );
	536	__submit( ctx, &idx, 1, true );
	537
	538	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
	539	/* paranoid */ verify( ! __preemption_enabled() );
	540	}
	541	#endif
[47746a2]	542	#endif

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