FreeBSD/Linux Kernel Cross Reference
sys/fs/mntfs/mntfs_vnops.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2020 Netflix, Inc.
      *
      * 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 ``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 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.
     *
     * $FreeBSD$
     */
    
    #include <sys/param.h>
    #include <sys/conf.h>
    #include <sys/mount.h>
    #include <sys/vnode.h>
    
    /*
     * The "mntfs" VCHR vnodes implemented here provide a safe way for file systems
     * to access their disk devices.  Using the normal devfs vnode has the problem
     * that if the device disappears, the devfs vnode is vgone'd as part of
     * removing it from the application-visible namespace, and some file systems
     * (notably FFS with softdep) get very unhappy if their dirty buffers are
     * invalidated out from under them.  By using a separate, private vnode,
     * file systems are able to clean up their buffer state in a controlled fashion
     * when the underlying device disappears.
     */
    
    static int
    mntfs_reclaim(struct vop_reclaim_args *ap)
    {
            struct vnode *vp = ap->a_vp;
    
            dev_rel(vp->v_rdev);
            return (0);
    }
    
    struct vop_vector mntfs_vnodeops = {
            .vop_default =          &default_vnodeops,
    
            .vop_fsync =            vop_stdfsync,
            .vop_strategy =         VOP_PANIC,
            .vop_reclaim =          mntfs_reclaim,
    };
    VFS_VOP_VECTOR_REGISTER(mntfs_vnodeops);
    
    /*
     * Allocate a private VCHR vnode for use by a mounted fs.
     * The underlying device will be the same as for the given vnode.
     * This mntfs vnode must be freed with mntfs_freevp() rather than just
     * releasing the reference.
     */
    struct vnode *
    mntfs_allocvp(struct mount *mp, struct vnode *ovp)
    {
            struct vnode *vp;
            struct cdev *dev;
    
            ASSERT_VOP_ELOCKED(ovp, __func__);
    
            dev = ovp->v_rdev;
    
            getnewvnode("mntfs", mp, &mntfs_vnodeops, &vp);
            vp->v_type = VCHR;
            vp->v_data = NULL;
            dev_ref(dev);
            vp->v_rdev = dev;
    
            VOP_UNLOCK(ovp);
            vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
            vn_set_state(vp, VSTATE_CONSTRUCTED);
            return (vp);
    }
    
    void
    mntfs_freevp(struct vnode *vp)
    {
            ASSERT_VOP_ELOCKED(vp, "mntfs_freevp");
            vgone(vp);
            vput(vp);
    }

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