/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 2001 Dag-Erling Smørgrav
 * All rights reserved.
 *
 * 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
 *    in this position and unchanged.
 * 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.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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>
#include "opt_pseudofs.h"

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>

#include <fs/pseudofs/pseudofs.h>
#include <fs/pseudofs/pseudofs_internal.h>

static MALLOC_DEFINE(M_PFSVNCACHE, "pfs_vncache", "pseudofs vnode cache");

static struct mtx pfs_vncache_mutex;
static eventhandler_tag pfs_exit_tag;
static void pfs_exit(void *arg, struct proc *p);
static void pfs_purge_all(void);

static SYSCTL_NODE(_vfs_pfs, OID_AUTO, vncache, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "pseudofs vnode cache");

static int pfs_vncache_entries;
SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, entries, CTLFLAG_RD,
    &pfs_vncache_entries, 0,
    "number of entries in the vnode cache");

static int pfs_vncache_maxentries;
SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, maxentries, CTLFLAG_RD,
    &pfs_vncache_maxentries, 0,
    "highest number of entries in the vnode cache");

static int pfs_vncache_hits;
SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, hits, CTLFLAG_RD,
    &pfs_vncache_hits, 0,
    "number of cache hits since initialization");

static int pfs_vncache_misses;
SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, misses, CTLFLAG_RD,
    &pfs_vncache_misses, 0,
    "number of cache misses since initialization");

extern struct vop_vector pfs_vnodeops;  /* XXX -> .h file */

static SLIST_HEAD(pfs_vncache_head, pfs_vdata) *pfs_vncache_hashtbl;
static u_long pfs_vncache_hash;
#define PFS_VNCACHE_HASH(pid)   (&pfs_vncache_hashtbl[(pid) & pfs_vncache_hash])

/*
 * Initialize vnode cache
 */
void
pfs_vncache_load(void)
{

        mtx_init(&pfs_vncache_mutex, "pfs_vncache", NULL, MTX_DEF);
        pfs_vncache_hashtbl = hashinit(maxproc / 4, M_PFSVNCACHE, &pfs_vncache_hash);
        pfs_exit_tag = EVENTHANDLER_REGISTER(process_exit, pfs_exit, NULL,
            EVENTHANDLER_PRI_ANY);
}

/*
 * Tear down vnode cache
 */
void
pfs_vncache_unload(void)
{

        EVENTHANDLER_DEREGISTER(process_exit, pfs_exit_tag);
        pfs_purge_all();
        KASSERT(pfs_vncache_entries == 0,
            ("%d vncache entries remaining", pfs_vncache_entries));
        mtx_destroy(&pfs_vncache_mutex);
        hashdestroy(pfs_vncache_hashtbl, M_PFSVNCACHE, pfs_vncache_hash);
}

/*
 * Allocate a vnode
 */
int
pfs_vncache_alloc(struct mount *mp, struct vnode **vpp,
                  struct pfs_node *pn, pid_t pid)
{
        struct pfs_vncache_head *hash;
        struct pfs_vdata *pvd, *pvd2;
        struct vnode *vp;
        enum vgetstate vs;
        int error;

        /*
         * See if the vnode is in the cache.
         */
        hash = PFS_VNCACHE_HASH(pid);
        if (SLIST_EMPTY(hash))
                goto alloc;
retry:
        mtx_lock(&pfs_vncache_mutex);
        SLIST_FOREACH(pvd, hash, pvd_hash) {
                if (pvd->pvd_pn == pn && pvd->pvd_pid == pid &&
                    pvd->pvd_vnode->v_mount == mp) {
                        vp = pvd->pvd_vnode;
                        vs = vget_prep(vp);
                        mtx_unlock(&pfs_vncache_mutex);
                        if (vget_finish(vp, LK_EXCLUSIVE, vs) == 0) {
                                ++pfs_vncache_hits;
                                *vpp = vp;
                                /*
                                 * Some callers cache_enter(vp) later, so
                                 * we have to make sure it's not in the
                                 * VFS cache so it doesn't get entered
                                 * twice.  A better solution would be to
                                 * make pfs_vncache_alloc() responsible
                                 * for entering the vnode in the VFS
                                 * cache.
                                 */
                                cache_purge(vp);
                                return (0);
                        }
                        goto retry;
                }
        }
        mtx_unlock(&pfs_vncache_mutex);
alloc:
        /* nope, get a new one */
        pvd = malloc(sizeof *pvd, M_PFSVNCACHE, M_WAITOK);
        error = getnewvnode("pseudofs", mp, &pfs_vnodeops, vpp);
        if (error) {
                free(pvd, M_PFSVNCACHE);
                return (error);
        }
        pvd->pvd_pn = pn;
        pvd->pvd_pid = pid;
        (*vpp)->v_data = pvd;
        switch (pn->pn_type) {
        case pfstype_root:
                (*vpp)->v_vflag = VV_ROOT;
#if 0
                printf("root vnode allocated\n");
#endif
                /* fall through */
        case pfstype_dir:
        case pfstype_this:
        case pfstype_parent:
        case pfstype_procdir:
                (*vpp)->v_type = VDIR;
                break;
        case pfstype_file:
                (*vpp)->v_type = VREG;
                break;
        case pfstype_symlink:
                (*vpp)->v_type = VLNK;
                break;
        case pfstype_none:
                KASSERT(0, ("pfs_vncache_alloc called for null node\n"));
        default:
                panic("%s has unexpected type: %d", pn->pn_name, pn->pn_type);
        }
        /*
         * Propagate flag through to vnode so users know it can change
         * if the process changes (i.e. execve)
         */
        if ((pn->pn_flags & PFS_PROCDEP) != 0)
                (*vpp)->v_vflag |= VV_PROCDEP;
        pvd->pvd_vnode = *vpp;
        vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY);
        VN_LOCK_AREC(*vpp);
        error = insmntque(*vpp, mp);
        if (error != 0) {
                free(pvd, M_PFSVNCACHE);
                *vpp = NULL;
                return (error);
        }
        vn_set_state(*vpp, VSTATE_CONSTRUCTED);
retry2:
        mtx_lock(&pfs_vncache_mutex);
        /*
         * Other thread may race with us, creating the entry we are
         * going to insert into the cache. Recheck after
         * pfs_vncache_mutex is reacquired.
         */
        SLIST_FOREACH(pvd2, hash, pvd_hash) {
                if (pvd2->pvd_pn == pn && pvd2->pvd_pid == pid &&
                    pvd2->pvd_vnode->v_mount == mp) {
                        vp = pvd2->pvd_vnode;
                        vs = vget_prep(vp);
                        mtx_unlock(&pfs_vncache_mutex);
                        if (vget_finish(vp, LK_EXCLUSIVE, vs) == 0) {
                                ++pfs_vncache_hits;
                                vgone(*vpp);
                                vput(*vpp);
                                *vpp = vp;
                                cache_purge(vp);
                                return (0);
                        }
                        goto retry2;
                }
        }
        ++pfs_vncache_misses;
        if (++pfs_vncache_entries > pfs_vncache_maxentries)
                pfs_vncache_maxentries = pfs_vncache_entries;
        SLIST_INSERT_HEAD(hash, pvd, pvd_hash);
        mtx_unlock(&pfs_vncache_mutex);
        return (0);
}

/*
 * Free a vnode
 */
int
pfs_vncache_free(struct vnode *vp)
{
        struct pfs_vdata *pvd, *pvd2;

        mtx_lock(&pfs_vncache_mutex);
        pvd = (struct pfs_vdata *)vp->v_data;
        KASSERT(pvd != NULL, ("pfs_vncache_free(): no vnode data\n"));
        SLIST_FOREACH(pvd2, PFS_VNCACHE_HASH(pvd->pvd_pid), pvd_hash) {
                if (pvd2 != pvd)
                        continue;
                SLIST_REMOVE(PFS_VNCACHE_HASH(pvd->pvd_pid), pvd, pfs_vdata, pvd_hash);
                --pfs_vncache_entries;
                break;
        }
        mtx_unlock(&pfs_vncache_mutex);

        free(pvd, M_PFSVNCACHE);
        vp->v_data = NULL;
        return (0);
}

/*
 * Purge the cache of dead entries
 *
 * The code is not very efficient and this perhaps can be addressed without
 * a complete rewrite. Previous iteration was walking a linked list from
 * scratch every time. This code only walks the relevant hash chain (if pid
 * is provided), but still resorts to scanning the entire cache at least twice
 * if a specific component is to be removed which is slower. This can be
 * augmented with resizing the hash.
 *
 * Explanation of the previous state:
 *
 * This is extremely inefficient due to the fact that vgone() not only
 * indirectly modifies the vnode cache, but may also sleep.  We can
 * neither hold pfs_vncache_mutex across a vgone() call, nor make any
 * assumptions about the state of the cache after vgone() returns.  In
 * consequence, we must start over after every vgone() call, and keep
 * trying until we manage to traverse the entire cache.
 *
 * The only way to improve this situation is to change the data structure
 * used to implement the cache.
 */

static void
pfs_purge_one(struct vnode *vnp)
{

        VOP_LOCK(vnp, LK_EXCLUSIVE);
        vgone(vnp);
        VOP_UNLOCK(vnp);
        vdrop(vnp);
}

void
pfs_purge(struct pfs_node *pn)
{
        struct pfs_vdata *pvd;
        struct vnode *vnp;
        u_long i, removed;

        mtx_lock(&pfs_vncache_mutex);
restart:
        removed = 0;
        for (i = 0; i <= pfs_vncache_hash; i++) {
restart_chain:
                SLIST_FOREACH(pvd, &pfs_vncache_hashtbl[i], pvd_hash) {
                        if (pn != NULL && pvd->pvd_pn != pn)
                                continue;
                        vnp = pvd->pvd_vnode;
                        vhold(vnp);
                        mtx_unlock(&pfs_vncache_mutex);
                        pfs_purge_one(vnp);
                        removed++;
                        mtx_lock(&pfs_vncache_mutex);
                        goto restart_chain;
                }
        }
        if (removed > 0)
                goto restart;
        mtx_unlock(&pfs_vncache_mutex);
}

static void
pfs_purge_all(void)
{

        pfs_purge(NULL);
}

/*
 * Free all vnodes associated with a defunct process
 */
static void
pfs_exit(void *arg, struct proc *p)
{
        struct pfs_vncache_head *hash;
        struct pfs_vdata *pvd;
        struct vnode *vnp;
        int pid;

        pid = p->p_pid;
        hash = PFS_VNCACHE_HASH(pid);
        if (SLIST_EMPTY(hash))
                return;
restart:
        mtx_lock(&pfs_vncache_mutex);
        SLIST_FOREACH(pvd, hash, pvd_hash) {
                if (pvd->pvd_pid != pid)
                        continue;
                vnp = pvd->pvd_vnode;
                vhold(vnp);
                mtx_unlock(&pfs_vncache_mutex);
                pfs_purge_one(vnp);
                goto restart;
        }
        mtx_unlock(&pfs_vncache_mutex);
}