// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/slab.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/init.h>
#include <linux/capability.h>

#include <xen/xen.h>
#include <xen/page.h>
#include <xen/xenbus.h>
#include <xen/xenbus_dev.h>
#include <xen/grant_table.h>
#include <xen/events.h>
#include <asm/xen/hypervisor.h>

#include "xenbus.h"

static int xenbus_backend_open(struct inode *inode, struct file *filp)
{
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        return nonseekable_open(inode, filp);
}

static long xenbus_alloc(domid_t domid)
{
        struct evtchn_alloc_unbound arg;
        int err = -EEXIST;

        xs_suspend();

        /* If xenstored_ready is nonzero, that means we have already talked to
         * xenstore and set up watches. These watches will be restored by
         * xs_resume, but that requires communication over the port established
         * below that is not visible to anyone until the ioctl returns.
         *
         * This can be resolved by splitting the ioctl into two parts
         * (postponing the resume until xenstored is active) but this is
         * unnecessarily complex for the intended use where xenstored is only
         * started once - so return -EEXIST if it's already running.
         */
        if (xenstored_ready)
                goto out_err;

        gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
                        virt_to_gfn(xen_store_interface), 0 /* writable */);

        arg.dom = DOMID_SELF;
        arg.remote_dom = domid;

        err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
        if (err)
                goto out_err;

        if (xen_store_evtchn > 0)
                xb_deinit_comms();

        xen_store_evtchn = arg.port;

        xs_resume();

        return arg.port;

 out_err:
        xs_suspend_cancel();
        return err;
}

static long xenbus_backend_ioctl(struct file *file, unsigned int cmd,
                                 unsigned long data)
{
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        switch (cmd) {
        case IOCTL_XENBUS_BACKEND_EVTCHN:
                if (xen_store_evtchn > 0)
                        return xen_store_evtchn;
                return -ENODEV;
        case IOCTL_XENBUS_BACKEND_SETUP:
                return xenbus_alloc(data);
        default:
                return -ENOTTY;
        }
}

static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
{
        size_t size = vma->vm_end - vma->vm_start;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
                return -EINVAL;

        if (remap_pfn_range(vma, vma->vm_start,
                            virt_to_pfn(xen_store_interface),
                            size, vma->vm_page_prot))
                return -EAGAIN;

        return 0;
}

static const struct file_operations xenbus_backend_fops = {
        .open = xenbus_backend_open,
        .mmap = xenbus_backend_mmap,
        .unlocked_ioctl = xenbus_backend_ioctl,
};

static struct miscdevice xenbus_backend_dev = {
        .minor = MISC_DYNAMIC_MINOR,
        .name = "xen/xenbus_backend",
        .fops = &xenbus_backend_fops,
};

static int __init xenbus_backend_init(void)
{
        int err;

        if (!xen_initial_domain())
                return -ENODEV;

        err = misc_register(&xenbus_backend_dev);
        if (err)
                pr_err("Could not register xenbus backend device\n");
        return err;
}
device_initcall(xenbus_backend_init);