implement POSIX asynchronous io

some features are not yet supported, and only minimal testing has been
performed. should be considered experimental at this point.

include/aio.h

+#ifndef _AIO_H
+#define _AIO_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
+ || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE)
+
+#include <signal.h>
+#include <time.h>
+
+#define __NEED_ssize_t
+#define __NEED_off_t
+
+#include <bits/alltypes.h>
+
+struct aiocb {
+	int aio_filedes, aio_lio_opcode, aio_reqprio;
+	volatile void *aio_buf;
+	size_t aio_nbytes;
+	struct sigevent aio_sigevent;
+	void *__td;
+	int __lock[2];
+	int __err;
+	ssize_t __ret;
+	off_t aio_offset;
+	void *__next, *__prev;
+	char __dummy4[32-2*sizeof(void *)];
+};
+
+#define AIO_CANCELED 0
+#define AIO_NOTCANCELED 1
+#define AIO_ALLDONE 2
+
+#define LIO_READ 0
+#define LIO_WRITE 1
+#define LIO_NOP 2
+
+#define LIO_WAIT 0
+#define LIO_NOWAIT 1
+
+int aio_read(struct aiocb *);
+int aio_write(struct aiocb *);
+int aio_error(struct aiocb *);
+ssize_t aio_return(struct aiocb *);
+int aio_cancel(int, struct aiocb *);
+int aio_suspend(struct aiocb *const [], int, const struct timespec *);
+int aio_fsync(int, struct aiocb *);
+
+int lio_listio(int, struct aiocb *const [], int, struct sigevent *);
+
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

src/aio/aio_cancel.c

+#include <aio.h>
+#include <pthread.h>
+#include <errno.h>
+
+int aio_cancel(int fd, struct aiocb *cb)
+{
+	if (!cb) {
+		/* FIXME: for correctness, we should return AIO_ALLDONE
+		 * if there are no outstanding aio operations on this
+		 * file descriptor, but that would require making aio
+		 * much slower, and seems to have little advantage since
+		 * we don't support cancellation anyway. */
+		return AIO_NOTCANCELED;
+	}
+	return cb->__err==EINPROGRESS ? AIO_NOTCANCELED : AIO_ALLDONE;
+}

src/aio/aio_error.c

+#include <aio.h>
+
+int aio_error(struct aiocb *cb)
+{
+	return cb->__err;
+}

src/aio/aio_fsync.c

+#include <aio.h>
+#include <errno.h>
+
+int aio_fsync(int op, struct aiocb *cb)
+{
+	/* FIXME: unsupported */
+	errno = EINVAL;
+	return -1;
+}

src/aio/aio_readwrite.c

+#include <aio.h>
+#include <fcntl.h>
+#include "pthread_impl.h"
+
+static void dummy(void)
+{
+}
+
+weak_alias(dummy, __aio_wake);
+
+static void notify_signal(struct sigevent *sev)
+{
+	siginfo_t si = {
+		.si_signo = sev->sigev_signo,
+		.si_value = sev->sigev_value,
+		.si_code = SI_ASYNCIO,
+		.si_pid = __pthread_self()->pid,
+		.si_uid = getuid()
+	};
+	__syscall(SYS_rt_sigqueueinfo, si.si_pid, si.si_signo, &si);
+}
+
+static void *io_thread(void *p)
+{
+	struct aiocb *cb = p;
+	int fd = cb->aio_filedes;
+	void *buf = (void *)cb->aio_buf;
+	size_t len = cb->aio_nbytes;
+	off_t off = cb->aio_offset;
+	int op = cb->aio_lio_opcode;
+	struct sigevent sev = cb->aio_sigevent;
+	ssize_t ret;
+
+	if (op == LIO_WRITE) {
+		if (  (fcntl(fd, F_GETFL) & O_APPEND)
+		    ||((ret = pwrite(fd, buf, len, off))<0 && errno==ESPIPE) )
+			ret = write(fd, buf, len);
+	} else if (op == LIO_READ) {
+		if ( (ret = pread(fd, buf, len, off))<0 && errno==ESPIPE )
+			ret = read(fd, buf, len);
+	} else {
+		ret = 0;
+	}
+	cb->__ret = ret;
+
+	if (ret < 0) a_store(&cb->__err, errno);
+	else a_store(&cb->__err, 0);
+
+	__aio_wake();
+
+	switch (cb->aio_sigevent.sigev_notify) {
+	case SIGEV_SIGNAL:
+		notify_signal(&sev);
+		break;
+	case SIGEV_THREAD:
+		sev.sigev_notify_function(sev.sigev_value);
+		break;
+	}
+
+	return 0;
+}
+
+static int new_req(struct aiocb *cb)
+{
+	int ret = 0;
+	pthread_attr_t a;
+	sigset_t set;
+	pthread_t td;
+
+	if (cb->aio_sigevent.sigev_notify == SIGEV_THREAD) {
+		if (cb->aio_sigevent.sigev_notify_attributes)
+			a = *cb->aio_sigevent.sigev_notify_attributes;
+		else
+			pthread_attr_init(&a);
+	} else {
+		pthread_attr_init(&a);
+		pthread_attr_setstacksize(&a, PAGE_SIZE);
+		pthread_attr_setguardsize(&a, 0);
+	}
+	pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
+	sigfillset(&set);
+	pthread_sigmask(SIG_BLOCK, &set, &set);
+	cb->__err = EINPROGRESS;
+	if (pthread_create(&td, &a, io_thread, cb)) {
+		errno = EAGAIN;
+		ret = -1;
+	}
+	pthread_sigmask(SIG_SETMASK, &set, 0);
+	cb->__td = td;
+
+	return ret;
+}
+
+ssize_t aio_read(struct aiocb *cb)
+{
+	cb->aio_lio_opcode = LIO_READ;
+	return new_req(cb);
+}
+
+ssize_t aio_write(struct aiocb *cb)
+{
+	cb->aio_lio_opcode = LIO_WRITE;
+	return new_req(cb);
+}

src/aio/aio_return.c

+#include <aio.h>
+
+ssize_t aio_return(struct aiocb *cb)
+{
+	return cb->__ret;
+}

src/aio/aio_suspend.c

+#include <aio.h>
+#include <errno.h>
+#include "pthread_impl.h"
+
+/* Due to the requirement that aio_suspend be async-signal-safe, we cannot
+ * use any locks, wait queues, etc. that would make it more efficient. The
+ * only obviously-correct algorithm is to generate a wakeup every time any
+ * aio operation finishes and have aio_suspend re-evaluate the completion
+ * status of each aiocb it was waiting on. */
+
+static volatile int seq;
+
+void __aio_wake(void)
+{
+	a_inc(&seq);
+	__wake(&seq, -1, 1);
+}
+
+int aio_suspend(struct aiocb *const cbs[], int cnt, const struct timespec *ts)
+{
+	int i, last, first=1, ret=0;
+	struct timespec at;
+
+	if (cnt<0) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	for (;;) {
+		last = seq;
+
+		for (i=0; i<cnt; i++) {
+			if (cbs[i] && cbs[i]->__err != EINPROGRESS)
+				return 0;
+		}
+
+		if (first && ts) {
+			clock_gettime(CLOCK_MONOTONIC, &at);
+			at.tv_sec += ts->tv_sec;
+			if ((at.tv_nsec += ts->tv_nsec) >= 1000000000) {
+				at.tv_nsec -= 1000000000;
+				at.tv_sec++;
+			}
+			first = 0;
+		}
+
+		ret = __timedwait(&seq, last, CLOCK_MONOTONIC,
+			ts ? &at : 0, 0, 0, 1);
+
+		if (ret == ETIMEDOUT) ret = EAGAIN;
+
+		if (ret) {
+			errno = ret;
+			return -1;
+		}
+	}
+}

src/aio/lio_listio.c

+#include <aio.h>
+#include <errno.h>
+#include "pthread_impl.h"
+
+struct lio_state {
+	struct sigevent *sev;
+	int cnt;
+	struct aiocb *cbs[];
+};
+
+static int lio_wait(struct lio_state *st)
+{
+	int i, err, got_err;
+	int cnt = st->cnt;
+	struct aiocb **cbs = st->cbs;
+
+	for (;;) {
+		for (i=0; i<cnt; i++) {
+			if (!cbs[i]) continue;
+			err = aio_error(cbs[i]);
+			if (err==EINPROGRESS)
+				break;
+			if (err) got_err=1;
+			cbs[i] = 0;
+		}
+		if (i==cnt) {
+			if (got_err) {
+				errno = EIO;
+				return -1;
+			}
+			return 0;
+		}
+		if (aio_suspend(cbs, cnt, 0))
+			return -1;
+	}
+}
+
+static void notify_signal(struct sigevent *sev)
+{
+	siginfo_t si = {
+		.si_signo = sev->sigev_signo,
+		.si_value = sev->sigev_value,
+		.si_code = SI_ASYNCIO,
+		.si_pid = __pthread_self()->pid,
+		.si_uid = getuid()
+	};
+	__syscall(SYS_rt_sigqueueinfo, si.si_pid, si.si_signo, &si);
+}
+
+static void *wait_thread(void *p)
+{
+	struct lio_state *st = p;
+	struct sigevent *sev = st->sev;
+	lio_wait(st);
+	free(st);
+	switch (sev->sigev_notify) {
+	case SIGEV_SIGNAL:
+		notify_signal(sev);
+		break;
+	case SIGEV_THREAD:
+		sev->sigev_notify_function(sev->sigev_value);
+		break;
+	}
+	return 0;
+}
+
+int lio_listio(int mode, struct aiocb *const cbs[], int cnt, struct sigevent *sev)
+{
+	int i, ret;
+	struct lio_state *st=0;
+
+	if (cnt < 0) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	if (mode == LIO_WAIT || (sev && sev->sigev_notify != SIGEV_NONE)) {
+		if (!(st = malloc(sizeof *st + cnt*sizeof *cbs))) {
+			errno = EAGAIN;
+			return -1;
+		}
+		st->cnt = cnt;
+		st->sev = sev;
+		memcpy(st->cbs, cbs, cnt*sizeof *cbs);
+	}
+
+	for (i=0; i<cnt; i++) {
+		if (!cbs[i]) continue;
+		switch (cbs[i]->aio_lio_opcode) {
+		case LIO_READ:
+			ret = aio_read(cbs[i]);
+			break;
+		case LIO_WRITE:
+			ret = aio_write(cbs[i]);
+			break;
+		default:
+			continue;
+		}
+		if (ret) {
+			free(st);
+			errno = EAGAIN;
+			return -1;
+		}
+	}
+
+	if (mode == LIO_WAIT) {
+		ret = lio_wait(st);
+		free(st);
+		return 0;
+	}
+
+	if (st) {
+		pthread_attr_t a;
+		sigset_t set;
+		pthread_t td;
+
+		if (sev->sigev_notify == SIGEV_THREAD) {
+			if (sev->sigev_notify_attributes)
+				a = *sev->sigev_notify_attributes;
+			else
+				pthread_attr_init(&a);
+		} else {
+			pthread_attr_init(&a);
+			pthread_attr_setstacksize(&a, PAGE_SIZE);
+			pthread_attr_setguardsize(&a, 0);
+		}
+		pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
+		sigfillset(&set);
+		pthread_sigmask(SIG_BLOCK, &set, &set);
+		if (pthread_create(&td, &a, wait_thread, st)) {
+			free(st);
+			errno = EAGAIN;
+			return -1;
+		}
+		pthread_sigmask(SIG_SETMASK, &set, 0);
+	}
+
+	return 0;
+}
+