sys_eventfd.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2014 Dmitry Chagin <dchagin@FreeBSD.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, 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 AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 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 OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/types.h>
#include <sys/user.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/filio.h>
#include <sys/stat.h>
#include <sys/errno.h>
#include <sys/event.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/uio.h>
#include <sys/selinfo.h>
#include <sys/eventfd.h>
 
#include <security/audit/audit.h>
 
_Static_assert(EFD_CLOEXEC == O_CLOEXEC, "Mismatched EFD_CLOEXEC");
_Static_assert(EFD_NONBLOCK == O_NONBLOCK, "Mismatched EFD_NONBLOCK");
 
MALLOC_DEFINE(M_EVENTFD, "eventfd", "eventfd structures");
 
static fo_rdwr_t        eventfd_read;
static fo_rdwr_t        eventfd_write;
static fo_ioctl_t       eventfd_ioctl;
static fo_poll_t        eventfd_poll;
static fo_kqfilter_t    eventfd_kqfilter;
static fo_stat_t        eventfd_stat;
static fo_close_t       eventfd_close;
static fo_fill_kinfo_t  eventfd_fill_kinfo;
 
static struct fileops eventfdops = {
        .fo_read = eventfd_read,
        .fo_write = eventfd_write,
        .fo_truncate = invfo_truncate,
        .fo_ioctl = eventfd_ioctl,
        .fo_poll = eventfd_poll,
        .fo_kqfilter = eventfd_kqfilter,
        .fo_stat = eventfd_stat,
        .fo_close = eventfd_close,
        .fo_chmod = invfo_chmod,
        .fo_chown = invfo_chown,
        .fo_sendfile = invfo_sendfile,
        .fo_fill_kinfo = eventfd_fill_kinfo,
        .fo_flags = DFLAG_PASSABLE
};
 
static void     filt_eventfddetach(struct knote *kn);
static int      filt_eventfdread(struct knote *kn, long hint);
static int      filt_eventfdwrite(struct knote *kn, long hint);
 
static struct filterops eventfd_rfiltops = {
        .f_isfd = 1,
        .f_detach = filt_eventfddetach,
        .f_event = filt_eventfdread
};
 
static struct filterops eventfd_wfiltops = {
        .f_isfd = 1,
        .f_detach = filt_eventfddetach,
        .f_event = filt_eventfdwrite
};
 
struct eventfd {
        eventfd_t       efd_count;
        uint32_t        efd_flags;
        struct selinfo  efd_sel;
        struct mtx      efd_lock;
};
 
int
eventfd_create_file(struct thread *td, struct file *fp, uint32_t initval,
    int flags)
{
        struct eventfd *efd;
        int fflags;
 
        AUDIT_ARG_FFLAGS(flags);
        AUDIT_ARG_VALUE(initval);
 
        efd = malloc(sizeof(*efd), M_EVENTFD, M_WAITOK | M_ZERO);
        efd->efd_flags = flags;
        efd->efd_count = initval;
        mtx_init(&efd->efd_lock, "eventfd", NULL, MTX_DEF);
        knlist_init_mtx(&efd->efd_sel.si_note, &efd->efd_lock);
 
        fflags = FREAD | FWRITE;
        if ((flags & EFD_NONBLOCK) != 0)
                fflags |= FNONBLOCK;
        finit(fp, fflags, DTYPE_EVENTFD, efd, &eventfdops);
 
        return (0);
}
 
static int
eventfd_close(struct file *fp, struct thread *td)
{
        struct eventfd *efd;
 
        efd = fp->f_data;
        seldrain(&efd->efd_sel);
        knlist_destroy(&efd->efd_sel.si_note);
        mtx_destroy(&efd->efd_lock);
        free(efd, M_EVENTFD);
        return (0);
}
 
static int
eventfd_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
        struct eventfd *efd;
        eventfd_t count;
        int error;
 
        if (uio->uio_resid < sizeof(eventfd_t))
                return (EINVAL);
 
        error = 0;
        efd = fp->f_data;
        mtx_lock(&efd->efd_lock);
        while (error == 0 && efd->efd_count == 0) {
                if ((fp->f_flag & FNONBLOCK) != 0) {
                        mtx_unlock(&efd->efd_lock);
                        return (EAGAIN);
                }
                error = mtx_sleep(&efd->efd_count, &efd->efd_lock, PCATCH,
                    "efdrd", 0);
        }
        if (error == 0) {
                MPASS(efd->efd_count > 0);
                if ((efd->efd_flags & EFD_SEMAPHORE) != 0) {
                        count = 1;
                        --efd->efd_count;
                } else {
                        count = efd->efd_count;
                        efd->efd_count = 0;
                }
                KNOTE_LOCKED(&efd->efd_sel.si_note, 0);
                selwakeup(&efd->efd_sel);
                wakeup(&efd->efd_count);
                mtx_unlock(&efd->efd_lock);
                error = uiomove(&count, sizeof(eventfd_t), uio);
        } else
                mtx_unlock(&efd->efd_lock);
 
        return (error);
}
 
static int
eventfd_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
        struct eventfd *efd;
        eventfd_t count;
        int error;
 
        if (uio->uio_resid < sizeof(eventfd_t))
                return (EINVAL);
 
        error = uiomove(&count, sizeof(eventfd_t), uio);
        if (error != 0)
                return (error);
        if (count == UINT64_MAX)
                return (EINVAL);
 
        efd = fp->f_data;
        mtx_lock(&efd->efd_lock);
retry:
        if (UINT64_MAX - efd->efd_count <= count) {
                if ((fp->f_flag & FNONBLOCK) != 0) {
                        mtx_unlock(&efd->efd_lock);
                        /* Do not not return the number of bytes written */
                        uio->uio_resid += sizeof(eventfd_t);
                        return (EAGAIN);
                }
                error = mtx_sleep(&efd->efd_count, &efd->efd_lock,
                    PCATCH, "efdwr", 0);
                if (error == 0)
                        goto retry;
        }
        if (error == 0) {
                MPASS(UINT64_MAX - efd->efd_count > count);
                efd->efd_count += count;
                KNOTE_LOCKED(&efd->efd_sel.si_note, 0);
                selwakeup(&efd->efd_sel);
                wakeup(&efd->efd_count);
        }
        mtx_unlock(&efd->efd_lock);
 
        return (error);
}
 
static int
eventfd_poll(struct file *fp, int events, struct ucred *active_cred,
    struct thread *td)
{
        struct eventfd *efd;
        int revents;
 
        efd = fp->f_data;
        revents = 0;
        mtx_lock(&efd->efd_lock);
        if ((events & (POLLIN | POLLRDNORM)) != 0 && efd->efd_count > 0)
                revents |= events & (POLLIN | POLLRDNORM);
        if ((events & (POLLOUT | POLLWRNORM)) != 0 && UINT64_MAX - 1 >
            efd->efd_count)
                revents |= events & (POLLOUT | POLLWRNORM);
        if (revents == 0)
                selrecord(td, &efd->efd_sel);
        mtx_unlock(&efd->efd_lock);
 
        return (revents);
}
 
static int
eventfd_kqfilter(struct file *fp, struct knote *kn)
{
        struct eventfd *efd = fp->f_data;
 
        mtx_lock(&efd->efd_lock);
        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &eventfd_rfiltops;
                break;
        case EVFILT_WRITE:
                kn->kn_fop = &eventfd_wfiltops;
                break;
        default:
                mtx_unlock(&efd->efd_lock);
                return (EINVAL);
        }
 
        kn->kn_hook = efd;
        knlist_add(&efd->efd_sel.si_note, kn, 1);
        mtx_unlock(&efd->efd_lock);
 
        return (0);
}
 
static void
filt_eventfddetach(struct knote *kn)
{
        struct eventfd *efd = kn->kn_hook;
 
        mtx_lock(&efd->efd_lock);
        knlist_remove(&efd->efd_sel.si_note, kn, 1);
        mtx_unlock(&efd->efd_lock);
}
 
static int
filt_eventfdread(struct knote *kn, long hint)
{
        struct eventfd *efd = kn->kn_hook;
        int ret;
 
        mtx_assert(&efd->efd_lock, MA_OWNED);
        kn->kn_data = (int64_t)efd->efd_count;
        ret = efd->efd_count > 0;
 
        return (ret);
}
 
static int
filt_eventfdwrite(struct knote *kn, long hint)
{
        struct eventfd *efd = kn->kn_hook;
        int ret;
 
        mtx_assert(&efd->efd_lock, MA_OWNED);
        kn->kn_data = (int64_t)(UINT64_MAX - 1 - efd->efd_count);
        ret = UINT64_MAX - 1 > efd->efd_count;
 
        return (ret);
}
 
static int
eventfd_ioctl(struct file *fp, u_long cmd, void *data,
    struct ucred *active_cred, struct thread *td)
{
        switch (cmd) {
        case FIONBIO:
        case FIOASYNC:
                return (0);
        }
 
        return (ENOTTY);
}
 
static int
eventfd_stat(struct file *fp, struct stat *st, struct ucred *active_cred)
{
        bzero((void *)st, sizeof *st);
        st->st_mode = S_IFIFO;
        return (0);
}
 
static int
eventfd_fill_kinfo(struct file *fp, struct kinfo_file *kif, struct filedesc *fdp)
{
        struct eventfd *efd = fp->f_data;
 
        kif->kf_type = KF_TYPE_EVENTFD;
        mtx_lock(&efd->efd_lock);
        kif->kf_un.kf_eventfd.kf_eventfd_value = efd->efd_count;
        kif->kf_un.kf_eventfd.kf_eventfd_flags = efd->efd_flags;
        mtx_unlock(&efd->efd_lock);
        return (0);
}