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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.
*/
#define EPOLL_FALLBACK 1
#include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */
#include <poll.h>
#include <linux/aio_abi.h>
#if EPOLL_FALLBACK
# include <sys/epoll.h>
#endif
/* we try to fill 4kB 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.
* therefore the calculation below will use "exactly" 4kB for the ring buffer
*/
#define EV_LINUXAIO_DEPTH (128 / 2 - 2 - 1) /* max. number of io events per batch */
/*****************************************************************************/
/* syscall wrapdadoop */
#include <sys/syscall.h> /* no glibc wrappers */
/* aio_abi.h is not versioned 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];
};
inline_size
int
ev_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
{
return syscall (SYS_io_setup, nr_events, ctx_idp);
}
inline_size
int
ev_io_destroy (aio_context_t ctx_id)
{
return syscall (SYS_io_destroy, ctx_id);
}
inline_size
int
ev_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[])
{
return syscall (SYS_io_submit, ctx_id, nr, cbp);
}
inline_size
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);
}
inline_size
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);
}
/*****************************************************************************/
/* actual backed implementation */
/* we use out own wrapper structure in acse we ever want to do something "clever" */
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, maybe use our own alocator? */
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, but array_needsize API doesn't support that */
(*base)->io.aio_lio_opcode = IOCB_CMD_POLL;
++base;
}
}
ecb_cold
static void
linuxaio_free_iocbp (EV_P)
{
while (linuxaio_iocbpmax--)
ev_free (linuxaio_iocbps [linuxaio_iocbpmax]);
linuxaio_iocbpmax = 0; /* next resize will completely reallocate the array, at some overhead */
}
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 EPOLL_FALLBACK
if (iocb->io.aio_reqprio < 0)
{
epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0);
iocb->io.aio_reqprio = 0;
}
#endif
if (iocb->io.aio_buf)
ev_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always returns an error 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 (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;
/* the kernel reads and writes both of these variables, */
/* as a C extension, we assume that volatile use here */
/* both makes reads atomic and once-only */
unsigned head = *(volatile unsigned *)&ring->head;
unsigned tail = *(volatile unsigned *)&ring->tail;
if (head == tail)
return 0;
/* bail out if the ring buffer doesn't match the expected layout */
if (expect_false (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]? */
return 0;
/* make sure the events up to tail are visible */
ECB_MEMORY_FENCE_ACQUIRE;
/* 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);
}
/* TODO: we only need a compiler barrier here, not a read fence */
ECB_MEMORY_FENCE_RELEASE;
/* as an extension to C, we hope that the volatile will make this atomic and once-only */
*(volatile unsigned *)&ring->head = tail;
/* make sure kernel can see our new head value - probably not required */
ECB_MEMORY_FENCE_RELEASE;
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[1];
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 degrades 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, sizeof (ioev) / sizeof (ioev [0]), ioev, &ts);
if (res < 0)
if (errno == EINTR)
/* ignored */;
else
ev_syserr ("(libev) linuxaio 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, res);
linuxaio_get_events_from_ring (EV_A);
}
}
#if EPOLL_FALLBACK
static void
linuxaio_rearm_epoll (EV_P_ struct iocb *iocb, int op)
{
struct epoll_event eev;
eev.events = EPOLLONESHOT;
if (iocb->aio_buf & POLLIN ) eev.events |= EPOLLIN ;
if (iocb->aio_buf & POLLOUT) eev.events |= EPOLLOUT;
eev.data.fd = iocb->aio_fildes;
if (epoll_ctl (backend_fd, op, iocb->aio_fildes, &eev) < 0)
ev_syserr ("(libeio) linuxaio epoll_ctl");
}
#endif
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 (expect_false (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 overflowed.
* In this case, we just try in next loop iteration.
* This should not result in a few fds taking priority, as the interface
* is one-shot, and we submit iocb's in a round-robin fashion.
*/
memmove (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits));
linuxaio_submitcnt -= submitted;
timeout = 0;
break;
}
#if EPOLL_FALLBACK
else if (errno == EINVAL)
{
/* This happens for unsupported fds, officially, but in my testing,
* also randomly happens for supported fds. We fall back to good old
* poll() here, under the assumption that this is a very rare case.
* See https://lore.kernel.org/patchwork/patch/1047453/ for evidence
* that the problem is known, but ignored.
*/
struct iocb *iocb = linuxaio_submits [submitted];
res = 1; /* skip this iocb */
linuxaio_rearm_epoll (EV_A_ iocb, EPOLL_CTL_ADD);
iocb->aio_reqprio = -1; /* mark iocb as epoll */
}
#endif
else
ev_syserr ("(libev) linuxaio io_submit");
submitted += res;
}
linuxaio_submitcnt = 0;
/* second phase: fetch and parse events */
linuxaio_get_events (EV_A_ timeout);
}
#if EPOLL_FALLBACK
static void
linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
{
struct epoll_event events[16];
for (;;)
{
int idx;
int res = epoll_wait (backend_fd, events, sizeof (events) / sizeof (events [0]), 0);
if (expect_false (res < 0))
ev_syserr ("(libev) linuxaio epoll_wait");
else if (!res)
break;
for (idx = res; idx--; )
{
int fd = events [idx].data.fd;
uint32_t ev = events [idx].events;
assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
linuxaio_rearm_epoll (EV_A_ &linuxaio_iocbps [fd]->io, EPOLL_CTL_MOD);
fd_event (EV_A_ fd,
(ev & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
| (ev & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0));
}
if (res < sizeof (events) / sizeof (events [0]))
break;
}
}
#endif
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 EPOLL_FALLBACK
/* 4.19 made epoll work */
if (ev_linux_version () < 0x041300)
return 0;
#else
/* 4.18 introduced IOCB_CMD_POLL */
if (ev_linux_version () < 0x041200)
return 0;
#endif
linuxaio_ctx = 0;
if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
return 0;
#if EPOLL_FALLBACK
backend_fd = ev_epoll_create ();
if (backend_fd < 0)
{
ev_io_destroy (linuxaio_ctx);
return 0;
}
ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
ev_io_start (EV_A_ &linuxaio_epoll_w);
ev_unref (EV_A); /* watcher should not keep loop alive */
#endif
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)
{
#if EPOLL_FALLBACK
close (backend_fd);
#endif
linuxaio_free_iocbp (EV_A);
ev_io_destroy (linuxaio_ctx);
}
inline_size
void
linuxaio_fork (EV_P)
{
/* this frees all iocbs, which is very heavy-handed */
linuxaio_destroy (EV_A);
linuxaio_submitcnt = 0; /* all pointers were invalidated */
linuxaio_ctx = 0;
while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
ev_syserr ("(libev) linuxaio io_setup");
#if EPOLL_FALLBACK
while ((backend_fd = ev_epoll_create ()) < 0)
ev_syserr ("(libev) linuxaio epoll_create");
ev_io_stop (EV_A_ &linuxaio_epoll_w);
ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
ev_io_start (EV_A_ &linuxaio_epoll_w);
#endif
fd_rearm_all (EV_A);
}