/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
 * All rights reserved.
 * Copyright (c) 2025 Mateusz Piotrowski <0mp@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 AUTHORS 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 AUTHORS 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/param.h>
#include <sys/bio.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/malloc.h>
#include <sys/queue.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/uio.h>
#include <sys/types.h>

#include <geom/geom.h>

#define G_ZERO_CLASS_NAME       "ZERO"

static int      g_zero_byte_sysctl(SYSCTL_HANDLER_ARGS);

SYSCTL_DECL(_kern_geom);
static SYSCTL_NODE(_kern_geom, OID_AUTO, zero, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "GEOM_ZERO stuff");
static int g_zero_clear = 1;
SYSCTL_INT(_kern_geom_zero, OID_AUTO, clear,
    CTLFLAG_RWTUN, &g_zero_clear, 0,
    "Clear read data buffer");
static int g_zero_byte = 0;
static uint8_t g_zero_buffer[PAGE_SIZE];
SYSCTL_PROC(_kern_geom_zero, OID_AUTO, byte,
    CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, &g_zero_byte, 0,
    g_zero_byte_sysctl, "I",
    "Byte (octet) value to clear the buffers with");

static struct g_provider *gpp;

static int
g_zero_byte_sysctl(SYSCTL_HANDLER_ARGS)
{
        int error;

        // XXX: Confirm that this is called on module load as well.
        // XXX: Shouldn't we lock here to avoid changing the byte value if the
        // driver is in the process of handling I/O?
        error = sysctl_handle_int(oidp, &g_zero_byte, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        memset(g_zero_buffer, g_zero_byte, PAGE_SIZE);
        return (0);
}

static void
g_zero_fill_pages(struct bio *bp)
{
        struct iovec aiovec;
        struct uio auio;
        size_t length;
        vm_offset_t offset;

        aiovec.iov_base = g_zero_buffer;
        aiovec.iov_len = PAGE_SIZE;
        auio.uio_iov = &aiovec;
        auio.uio_iovcnt = 1;
        auio.uio_offset = 0;
        auio.uio_segflg = UIO_SYSSPACE;
        auio.uio_rw = UIO_WRITE;
        auio.uio_td = curthread;

        /*
         * To handle the unmapped I/O request, we need to fill the pages in the
         * bp->bio_ma array with the g_zero_byte value. However, instead of
         * setting every byte individually, we use uiomove_fromphys() to fill a
         * page at a time with g_zero_buffer.
         */
        bp->bio_resid = bp->bio_length;
        offset = bp->bio_ma_offset & PAGE_MASK;
        for (int i = 0; i < bp->bio_ma_n && bp->bio_resid > 0; i++) {
                length = MIN(PAGE_SIZE - offset, bp->bio_resid);
                auio.uio_resid = length;

                (void)uiomove_fromphys(&bp->bio_ma[i], offset, length, &auio);

                offset = 0;
                bp->bio_resid -= length;
        }
}


static void
g_zero_start(struct bio *bp)
{
        int error;

        switch (bp->bio_cmd) {
        case BIO_READ:
                if (g_zero_clear) {
                        if ((bp->bio_flags & BIO_UNMAPPED) != 0)
                                g_zero_fill_pages(bp);
                        else
                                memset(bp->bio_data, g_zero_byte,
                                    bp->bio_length);
                }
                /* FALLTHROUGH */
        case BIO_DELETE:
        case BIO_WRITE:
                bp->bio_completed = bp->bio_length;
                error = 0;
                break;
        case BIO_GETATTR:
        default:
                error = EOPNOTSUPP;
                break;
        }
        g_io_deliver(bp, error);
}

static void
g_zero_init(struct g_class *mp)
{
        struct g_geom *gp;
        struct g_provider *pp;

        g_topology_assert();
        gp = g_new_geom(mp, "gzero");
        gp->start = g_zero_start;
        gp->access = g_std_access;
        gpp = pp = g_new_providerf(gp, "%s", gp->name);
        pp->flags |= G_PF_ACCEPT_UNMAPPED | G_PF_DIRECT_SEND |
            G_PF_DIRECT_RECEIVE;
        pp->mediasize = 1152921504606846976LLU;
        pp->sectorsize = 512;
        g_error_provider(pp, 0);
}

static int
g_zero_destroy_geom(struct gctl_req *req __unused, struct g_class *mp __unused,
    struct g_geom *gp)
{
        struct g_provider *pp;

        g_topology_assert();
        if (gp == NULL)
                return (0);
        pp = LIST_FIRST(&gp->provider);
        if (pp == NULL)
                return (0);
        if (pp->acr > 0 || pp->acw > 0 || pp->ace > 0)
                return (EBUSY);
        gpp = NULL;
        g_wither_geom(gp, ENXIO);
        return (0);
}

static struct g_class g_zero_class = {
        .name = G_ZERO_CLASS_NAME,
        .version = G_VERSION,
        .init = g_zero_init,
        .destroy_geom = g_zero_destroy_geom
};

DECLARE_GEOM_CLASS(g_zero_class, g_zero);
MODULE_VERSION(geom_zero, 0);