/*      $NetBSD: union_vfsops.c,v 1.88 2024/05/18 00:04:46 thorpej Exp $        */

/*
 * Copyright (c) 1994 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software donated to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      @(#)union_vfsops.c      8.20 (Berkeley) 5/20/95
 */

/*
 * Copyright (c) 1994 Jan-Simon Pendry.
 * All rights reserved.
 *
 * This code is derived from software donated to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      @(#)union_vfsops.c      8.20 (Berkeley) 5/20/95
 */

/*
 * Union Layer
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: union_vfsops.c,v 1.88 2024/05/18 00:04:46 thorpej Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysctl.h>
#include <sys/time.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/filedesc.h>
#include <sys/queue.h>
#include <sys/stat.h>
#include <sys/kauth.h>
#include <sys/module.h>

#include <miscfs/genfs/genfs.h>
#include <fs/union/union.h>

MODULE(MODULE_CLASS_VFS, union, NULL);

/*
 * Mount union filesystem
 */
int
union_mount(struct mount *mp, const char *path, void *data, size_t *data_len)
{
        struct lwp *l = curlwp;
        int error = 0;
        struct union_args *args = data;
        struct vnode *lowerrootvp = NULLVP;
        struct vnode *upperrootvp = NULLVP;
        struct union_mount *um = 0;
        const char *cp;
        char *xp;
        int len;
        size_t size;

        if (args == NULL)
                return EINVAL;
        if (*data_len < sizeof *args)
                return EINVAL;

#ifdef UNION_DIAGNOSTIC
        printf("%s(mp = %p)\n", __func__, mp);
#endif

        if (mp->mnt_flag & MNT_GETARGS) {
                um = MOUNTTOUNIONMOUNT(mp);
                if (um == NULL)
                        return EIO;
                args->target = NULL;
                args->mntflags = um->um_op;
                *data_len = sizeof *args;
                return 0;
        }
        /*
         * Update is a no-op
         */
        if (mp->mnt_flag & MNT_UPDATE) {
                /*
                 * Need to provide.
                 * 1. a way to convert between rdonly and rdwr mounts.
                 * 2. support for nfs exports.
                 */
                error = EOPNOTSUPP;
                goto bad;
        }

        lowerrootvp = mp->mnt_vnodecovered;
        vref(lowerrootvp);

        /*
         * Find upper node.
         */
        error = namei_simple_user(args->target,
            NSM_FOLLOW_NOEMULROOT, &upperrootvp);
        if (error != 0)
                goto bad;

        if (upperrootvp->v_type != VDIR) {
                error = EINVAL;
                goto bad;
        }

        um = kmem_zalloc(sizeof(*um), KM_SLEEP);

        /*
         * Keep a held reference to the target vnodes.
         * They are vrele'd in union_unmount.
         *
         * Depending on the _BELOW flag, the filesystems are
         * viewed in a different order.  In effect, this is the
         * same as providing a mount under option to the mount syscall.
         */

        um->um_op = args->mntflags & UNMNT_OPMASK;
        switch (um->um_op) {
        case UNMNT_ABOVE:
                um->um_lowervp = lowerrootvp;
                um->um_uppervp = upperrootvp;
                break;

        case UNMNT_BELOW:
                um->um_lowervp = upperrootvp;
                um->um_uppervp = lowerrootvp;
                break;

        case UNMNT_REPLACE:
                vrele(lowerrootvp);
                lowerrootvp = NULLVP;
                um->um_uppervp = upperrootvp;
                um->um_lowervp = lowerrootvp;
                break;

        default:
                error = EINVAL;
                goto bad;
        }

        /*
         * This mount is mp-safe if both lower mounts are mp-safe.
         */

        if (((um->um_lowervp == NULLVP) ||
            (um->um_lowervp->v_mount->mnt_iflag & IMNT_MPSAFE)) &&
            (um->um_uppervp->v_mount->mnt_iflag & IMNT_MPSAFE))
                mp->mnt_iflag |= IMNT_MPSAFE;

        /*
         * Unless the mount is readonly, ensure that the top layer
         * supports whiteout operations
         */
        if ((mp->mnt_flag & MNT_RDONLY) == 0) {
                static struct componentname nullcn = {
                        .cn_nameiop = LOOKUP,
                        .cn_cred = NOCRED
                };

                vn_lock(um->um_uppervp, LK_EXCLUSIVE | LK_RETRY);
                error = VOP_WHITEOUT(um->um_uppervp, &nullcn, LOOKUP);
                VOP_UNLOCK(um->um_uppervp);
                if (error)
                        goto bad;
        }

        um->um_cred = l->l_cred;
        kauth_cred_hold(um->um_cred);
        um->um_cmode = UN_DIRMODE &~ l->l_proc->p_cwdi->cwdi_cmask;

        /*
         * Depending on what you think the MNT_LOCAL flag might mean,
         * you may want the && to be || on the conditional below.
         * At the moment it has been defined that the filesystem is
         * only local if it is all local, ie the MNT_LOCAL flag implies
         * that the entire namespace is local.  If you think the MNT_LOCAL
         * flag implies that some of the files might be stored locally
         * then you will want to change the conditional.
         */
        if (um->um_op == UNMNT_ABOVE) {
                if (((um->um_lowervp == NULLVP) ||
                     (um->um_lowervp->v_mount->mnt_flag & MNT_LOCAL)) &&
                    (um->um_uppervp->v_mount->mnt_flag & MNT_LOCAL))
                        mp->mnt_flag |= MNT_LOCAL;
        }

        /*
         * Copy in the upper layer's RDONLY flag.  This is for the benefit
         * of lookup() which explicitly checks the flag, rather than asking
         * the filesystem for its own opinion.  This means, that an update
         * mount of the underlying filesystem to go from rdonly to rdwr
         * will leave the unioned view as read-only.
         */
        mp->mnt_flag |= (um->um_uppervp->v_mount->mnt_flag & MNT_RDONLY);

        mp->mnt_data = um;
        vfs_getnewfsid(mp);

        error = set_statvfs_info(path, UIO_USERSPACE, NULL, UIO_USERSPACE,
            mp->mnt_op->vfs_name, mp, l);
        if (error)
                goto bad;

        error = vfs_set_lowermount(mp, um->um_uppervp->v_mount);
        if (error)
                goto bad;

        switch (um->um_op) {
        case UNMNT_ABOVE:
                cp = "<above>:";
                break;
        case UNMNT_BELOW:
                cp = "<below>:";
                break;
        case UNMNT_REPLACE:
                cp = "";
                break;
        default:
                cp = "<invalid>:";
#ifdef DIAGNOSTIC
                panic("%s: bad um_op", __func__);
#endif
                break;
        }
        len = strlen(cp);
        memcpy(mp->mnt_stat.f_mntfromname, cp, len);

        xp = mp->mnt_stat.f_mntfromname + len;
        len = MNAMELEN - len;

        (void) copyinstr(args->target, xp, len - 1, &size);
        memset(xp + size, 0, len - size);

#ifdef UNION_DIAGNOSTIC
        printf("%s: from %s, on %s\n", __func__,
            mp->mnt_stat.f_mntfromname, mp->mnt_stat.f_mntonname);
#endif

        /* Setup the readdir hook if it's not set already */
        if (!vn_union_readdir_hook)
                vn_union_readdir_hook = union_readdirhook;

        return 0;

bad:
        if (um) {
                if (um->um_cred)
                        kauth_cred_free(um->um_cred);
                kmem_free(um, sizeof(*um));
        }
        if (upperrootvp)
                vrele(upperrootvp);
        if (lowerrootvp)
                vrele(lowerrootvp);
        return error;
}

/*
 * VFS start.  Nothing needed here - the start routine
 * on the underlying filesystem(s) will have been called
 * when that filesystem was mounted.
 */
 /*ARGSUSED*/
int
union_start(struct mount *mp, int flags)
{

        return 0;
}

/*
 * Free reference to union layer
 */
static bool
union_unmount_selector(void *cl, struct vnode *vp)
{
        int *count = cl;

        KASSERT(mutex_owned(vp->v_interlock));

        *count += 1;
        return false;
}

int
union_unmount(struct mount *mp, int mntflags)
{
        struct union_mount *um = MOUNTTOUNIONMOUNT(mp);
        int freeing;
        int error;

#ifdef UNION_DIAGNOSTIC
        printf("%s(mp = %p)\n", __func__, mp);
#endif

        /*
         * Keep flushing vnodes from the mount list.
         * This is needed because of the un_pvp held
         * reference to the parent vnode.
         * If more vnodes have been freed on a given pass,
         * the try again.  The loop will iterate at most
         * (d) times, where (d) is the maximum tree depth
         * in the filesystem.
         */
        for (freeing = 0; (error = vflush(mp, NULL, 0)) != 0;) {
                struct vnode_iterator *marker;
                int n;

                /* count #vnodes held on mount list */
                n = 0;
                vfs_vnode_iterator_init(mp, &marker);
                vfs_vnode_iterator_next(marker, union_unmount_selector, &n);
                vfs_vnode_iterator_destroy(marker);

                /* if this is unchanged then stop */
                if (n == freeing)
                        break;

                /* otherwise try once more time */
                freeing = n;
        }

        /*
         * Ok, now that we've tried doing it gently, get out the hammer.
         */

        if (mntflags & MNT_FORCE)
                error = vflush(mp, NULL, FORCECLOSE);

        if (error)
                return error;

        /*
         * Discard references to upper and lower target vnodes.
         */
        if (um->um_lowervp)
                vrele(um->um_lowervp);
        vrele(um->um_uppervp);
        kauth_cred_free(um->um_cred);
        /*
         * Finally, throw away the union_mount structure
         */
        kmem_free(um, sizeof(*um));
        mp->mnt_data = NULL;
        return 0;
}

int
union_root(struct mount *mp, int lktype, struct vnode **vpp)
{
        struct union_mount *um = MOUNTTOUNIONMOUNT(mp);
        int error;

        /*
         * Return locked reference to root.
         */
        vref(um->um_uppervp);
        if (um->um_lowervp)
                vref(um->um_lowervp);
        error = union_allocvp(vpp, mp, NULL, NULL, NULL,
            um->um_uppervp, um->um_lowervp, 1);

        if (error) {
                vrele(um->um_uppervp);
                if (um->um_lowervp)
                        vrele(um->um_lowervp);
                return error;
        }

        vn_lock(*vpp, lktype | LK_RETRY);

        return 0;
}

int
union_statvfs(struct mount *mp, struct statvfs *sbp)
{
        int error;
        struct union_mount *um = MOUNTTOUNIONMOUNT(mp);
        struct statvfs *sbuf = kmem_zalloc(sizeof(*sbuf), KM_SLEEP);
        unsigned long lbsize;

#ifdef UNION_DIAGNOSTIC
        printf("%s(mp = %p, lvp = %p, uvp = %p)\n", __func__, mp,
            um->um_lowervp, um->um_uppervp);
#endif

        if (um->um_lowervp) {
                error = VFS_STATVFS(um->um_lowervp->v_mount, sbuf);
                if (error)
                        goto done;
        }

        /* now copy across the "interesting" information and fake the rest */
        lbsize = sbuf->f_bsize;
        sbp->f_blocks = sbuf->f_blocks - sbuf->f_bfree;
        sbp->f_files = sbuf->f_files - sbuf->f_ffree;

        error = VFS_STATVFS(um->um_uppervp->v_mount, sbuf);
        if (error)
                goto done;

        sbp->f_flag = sbuf->f_flag;
        sbp->f_bsize = sbuf->f_bsize;
        sbp->f_frsize = sbuf->f_frsize;
        sbp->f_iosize = sbuf->f_iosize;

        /*
         * The "total" fields count total resources in all layers,
         * the "free" fields count only those resources which are
         * free in the upper layer (since only the upper layer
         * is writable).
         */

        if (sbuf->f_bsize != lbsize)
                sbp->f_blocks = sbp->f_blocks * lbsize / sbuf->f_bsize;
        sbp->f_blocks += sbuf->f_blocks;
        sbp->f_bfree = sbuf->f_bfree;
        sbp->f_bavail = sbuf->f_bavail;
        sbp->f_bresvd = sbuf->f_bresvd;
        sbp->f_files += sbuf->f_files;
        sbp->f_ffree = sbuf->f_ffree;
        sbp->f_favail = sbuf->f_favail;
        sbp->f_fresvd = sbuf->f_fresvd;

        copy_statvfs_info(sbp, mp);
done:
        kmem_free(sbuf, sizeof(*sbuf));
        return error;
}

/*ARGSUSED*/
int
union_sync(struct mount *mp, int waitfor, kauth_cred_t cred)
{

        /*
         * XXX - Assumes no data cached at union layer.
         */
        return 0;
}

/*ARGSUSED*/
int
union_vget(struct mount *mp, ino_t ino, int lktype, struct vnode **vpp)
{

        return EOPNOTSUPP;
}

static int
union_renamelock_enter(struct mount *mp)
{
        struct union_mount *um = MOUNTTOUNIONMOUNT(mp);

        /* Lock just the upper fs, where the action happens. */
        return VFS_RENAMELOCK_ENTER(um->um_uppervp->v_mount);
}

static void
union_renamelock_exit(struct mount *mp)
{
        struct union_mount *um = MOUNTTOUNIONMOUNT(mp);

        VFS_RENAMELOCK_EXIT(um->um_uppervp->v_mount);
}

extern const struct vnodeopv_desc union_vnodeop_opv_desc;

const struct vnodeopv_desc * const union_vnodeopv_descs[] = {
        &union_vnodeop_opv_desc,
        NULL,
};

struct vfsops union_vfsops = {
        .vfs_name = MOUNT_UNION,
        .vfs_min_mount_data = sizeof (struct union_args),
        .vfs_mount = union_mount,
        .vfs_start = union_start,
        .vfs_unmount = union_unmount,
        .vfs_root = union_root,
        .vfs_quotactl = (void *)eopnotsupp,
        .vfs_statvfs = union_statvfs,
        .vfs_sync = union_sync,
        .vfs_vget = union_vget,
        .vfs_loadvnode = union_loadvnode,
        .vfs_fhtovp = (void *)eopnotsupp,
        .vfs_vptofh = (void *)eopnotsupp,
        .vfs_init = union_init,
        .vfs_reinit = union_reinit,
        .vfs_done = union_done,
        .vfs_snapshot = (void *)eopnotsupp,
        .vfs_extattrctl = vfs_stdextattrctl,
        .vfs_suspendctl = genfs_suspendctl,
        .vfs_renamelock_enter = union_renamelock_enter,
        .vfs_renamelock_exit = union_renamelock_exit,
        .vfs_fsync = (void *)eopnotsupp,
        .vfs_opv_descs = union_vnodeopv_descs
};

SYSCTL_SETUP(unionfs_sysctl_setup, "unionfs sysctl")
{

        sysctl_createv(clog, 0, NULL, NULL,
            CTLFLAG_PERMANENT,
            CTLTYPE_NODE, "union",
            SYSCTL_DESCR("Union file system"),
            NULL, 0, NULL, 0,
            CTL_VFS, 15, CTL_EOL);
        /*
         * XXX the "15" above could be dynamic, thereby eliminating
         * one more instance of the "number to vfs" mapping problem,
         * but "15" is the order as taken from sys/mount.h
         */
}

static int
union_modcmd(modcmd_t cmd, void *arg)
{

        switch (cmd) {
        case MODULE_CMD_INIT:
                return vfs_attach(&union_vfsops);
        case MODULE_CMD_FINI:
                return vfs_detach(&union_vfsops);
        default:
                return ENOTTY;
        }
}