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/*
* libev linux aio fd activity backend
*
* Copyright (c) 2019 Marc Alexander Lehmann <libev@schmorp.de>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modifica-
* tion, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
* CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
* CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
* ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Alternatively, the contents of this file may be used under the terms of
* the GNU General Public License ("GPL") version 2 or any later version,
* in which case the provisions of the GPL are applicable instead of
* the above. If you wish to allow the use of your version of this file
* only under the terms of the GPL and not to allow others to use your
* version of this file under the BSD license, indicate your decision
* by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL. If you do not delete the
* provisions above, a recipient may use your version of this file under
* either the BSD or the GPL.
*/
#include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */
#include <poll.h>
#include <linux/aio_abi.h>
/* we try to fill 4kn pages exactly.
* the ring buffer header is 32 bytes, every io event is 32 bytes.
* the kernel takes the io event number, doubles it, adds 2, adds the ring buffer
* so the calculation below will use "exactly" 8kB for the ring buffer
*/
#define EV_LINUXAIO_DEPTH (256 / 2 - 2 - 1) /* max. number of io events per batch */
/*****************************************************************************/
/* syscall wrapdadoop */
#include <sys/syscall.h> /* no glibc wrappers */
/* aio_abi.h is not verioned in any way, so we cannot test for its existance */
#define IOCB_CMD_POLL 5
/* taken from linux/fs/aio.c */
#define AIO_RING_MAGIC 0xa10a10a1
#define AIO_RING_INCOMPAT_FEATURES 0
struct aio_ring
{
unsigned id; /* kernel internal index number */
unsigned nr; /* number of io_events */
unsigned head; /* Written to by userland or by kernel. */
unsigned tail;
unsigned magic;
unsigned compat_features;
unsigned incompat_features;
unsigned header_length; /* size of aio_ring */
struct io_event io_events[0];
};
static int
ev_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
{
return syscall (SYS_io_setup, nr_events, ctx_idp);
}
static int
ev_io_destroy (aio_context_t ctx_id)
{
return syscall (SYS_io_destroy, ctx_id);
}
static int
ev_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[])
{
return syscall (SYS_io_submit, ctx_id, nr, cbp);
}
static int
ev_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result)
{
return syscall (SYS_io_cancel, ctx_id, cbp, result);
}
static int
ev_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout)
{
return syscall (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout);
}
typedef void (*ev_io_cb) (long nr, struct io_event *events);
/*****************************************************************************/
/* actual backed implementation */
/* two iocbs for every fd, one for read, one for write */
typedef struct aniocb
{
struct iocb io;
/*int inuse;*/
} *ANIOCBP;
inline_size
void
linuxaio_array_needsize_iocbp (ANIOCBP *base, int count)
{
/* TODO: quite the overhead to allocate every iocb separately */
while (count--)
{
*base = (ANIOCBP)ev_malloc (sizeof (**base));
/* TODO: full zero initialize required? */
memset (*base, 0, sizeof (**base));
/* would be nice to initialize fd/data as well */
(*base)->io.aio_lio_opcode = IOCB_CMD_POLL;
++base;
}
}
static void
linuxaio_free_iocbp (EV_P)
{
while (linuxaio_iocbpmax--)
ev_free (linuxaio_iocbps [linuxaio_iocbpmax]);
/* next resize will completely reallocate the array */
linuxaio_iocbpmax = 0;
linuxaio_submitcnt = 0; /* all pointers invalidated */
}
static void
linuxaio_modify (EV_P_ int fd, int oev, int nev)
{
array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp);
struct aniocb *iocb = linuxaio_iocbps [fd];
if (iocb->io.aio_buf)
ev_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always fails in relevant kernels */
if (nev)
{
iocb->io.aio_data = fd;
iocb->io.aio_fildes = fd;
iocb->io.aio_buf =
(nev & EV_READ ? POLLIN : 0)
| (nev & EV_WRITE ? POLLOUT : 0);
/* queue iocb up for io_submit */
/* this assumes we only ever get one call per fd per loop iteration */
++linuxaio_submitcnt;
array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit);
linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
}
}
static void
linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
{
while (nr)
{
int fd = ev->data;
int res = ev->res;
assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
/* linux aio is oneshot: rearm fd */
linuxaio_iocbps [fd]->io.aio_buf = 0;
anfds [fd].events = 0;
fd_change (EV_A_ fd, 0);
/* feed events, we do not expect or handle POLLNVAL */
if (ecb_expect_false (res & POLLNVAL))
fd_kill (EV_A_ fd);
else
fd_event (
EV_A_
fd,
(res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
| (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
);
--nr;
++ev;
}
}
/* get any events from ringbuffer, return true if any were handled */
static int
linuxaio_get_events_from_ring (EV_P)
{
struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
ECB_MEMORY_FENCE_ACQUIRE;
unsigned head = ring->head;
unsigned tail = *(volatile unsigned *)&ring->tail;
if (ring->magic != AIO_RING_MAGIC
|| ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
|| ring->header_length != sizeof (struct aio_ring) /* TODO: or use it to find io_event[0]? */
|| head == tail)
return 0;
/* parse all available events, but only once, to avoid starvation */
if (tail > head) /* normal case around */
linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head);
else
{
/* wrapped around */
linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
linuxaio_parse_events (EV_A_ ring->io_events, tail);
}
ring->head = tail;
return 1;
}
/* read at least one event from kernel, or timeout */
inline_size
void
linuxaio_get_events (EV_P_ ev_tstamp timeout)
{
struct timespec ts;
struct io_event ioev;
int res;
if (linuxaio_get_events_from_ring (EV_A))
return;
/* no events, so wait for at least one, then poll ring buffer again */
/* this degraded to one event per loop iteration */
/* if the ring buffer changes layout, but so be it */
ts.tv_sec = (long)timeout;
ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9);
res = ev_io_getevents (linuxaio_ctx, 1, 1, &ioev, &ts);
if (res < 0)
ev_syserr ("(libev) io_getevents");
else if (res)
{
/* at least one event received, handle it and any remaining ones in the ring buffer */
linuxaio_parse_events (EV_A_ &ioev, 1);
linuxaio_get_events_from_ring (EV_A);
}
}
static void
linuxaio_poll (EV_P_ ev_tstamp timeout)
{
int submitted;
/* first phase: submit new iocbs */
/* io_submit might return less than the requested number of iocbs */
/* this is, afaics, only because of errors, but we go by the book and use a loop, */
/* which allows us to pinpoint the errornous iocb */
for (submitted = 0; submitted < linuxaio_submitcnt; )
{
int res = ev_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
if (res < 0)
if (errno == EAGAIN)
{
/* This happens when the ring buffer is full, at least. I assume this means
* that the event was queued synchronously during io_submit, and thus
* the buffer overflowd.
* In this case, we just try next loop iteration.
*/
memcpy (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits));
linuxaio_submitcnt -= submitted;
timeout = 0;
break;
}
else
/* TODO: we get EAGAIN when the ring buffer is full for some reason */
/* TODO: should we always just try next time? */
ev_syserr ("(libev) io_submit");
submitted += res;
}
linuxaio_submitcnt = 0;
/* second phase: fetch and parse events */
linuxaio_get_events (EV_A_ timeout);
}
inline_size
int
linuxaio_init (EV_P_ int flags)
{
/* would be great to have a nice test for IOCB_CMD_POLL instead */
/* also: test some semi-common fd types, such as files and ttys in recommended_backends */
if (ev_linux_version () < 0x041200) /* 4.18 introduced IOCB_CMD_POLL */
return 0;
linuxaio_ctx = 0;
if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
return 0;
backend_modify = linuxaio_modify;
backend_poll = linuxaio_poll;
linuxaio_iocbpmax = 0;
linuxaio_iocbps = 0;
linuxaio_submits = 0;
linuxaio_submitmax = 0;
linuxaio_submitcnt = 0;
return EVBACKEND_LINUXAIO;
}
inline_size
void
linuxaio_destroy (EV_P)
{
linuxaio_free_iocbp (EV_A);
ev_io_destroy (linuxaio_ctx);
}
inline_size
void
linuxaio_fork (EV_P)
{
/* TODO: verify and test */
linuxaio_destroy (EV_A);
linuxaio_ctx = 0;
while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
ev_syserr ("(libev) io_setup");
fd_rearm_all (EV_A);
}