Function vtryrecycle

freebsd/kern/vfs_subr.c:1577–1631

* Try to recycle a freed vnode. We abort if anyone picks up a reference * before we actually vgone(). This function must be called with the vnode * held to prevent the vnode from being returned to the free list midway * through vgone(). */

 * through vgone().
 */
static int
vtryrecycle(struct vnode *vp)
{
	struct mount *vnmp;

	CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
	VNASSERT(vp->v_holdcnt, vp,
	    ("vtryrecycle: Recycling vp %p without a reference.", vp));
	/*
	 * This vnode may found and locked via some other list, if so we
	 * can't recycle it yet.
	 */
	if (VOP_LOCK(vp, LK_EXCLUSIVE | LK_NOWAIT) != 0) {
		CTR2(KTR_VFS,
		    "%s: impossible to recycle, vp %p lock is already held",
		    __func__, vp);
		vdrop(vp);
		return (EWOULDBLOCK);
	}
	/*
	 * Don't recycle if its filesystem is being suspended.
	 */
	if (vn_start_write(vp, &vnmp, V_NOWAIT) != 0) {
		VOP_UNLOCK(vp);
		CTR2(KTR_VFS,
		    "%s: impossible to recycle, cannot start the write for %p",
		    __func__, vp);
		vdrop(vp);
		return (EBUSY);
	}
	/*
	 * If we got this far, we need to acquire the interlock and see if
	 * anyone picked up this vnode from another list.  If not, we will
	 * mark it with DOOMED via vgonel() so that anyone who does find it
	 * will skip over it.
	 */
	VI_LOCK(vp);
	if (vp->v_usecount) {
		VOP_UNLOCK(vp);
		vdropl(vp);
		vn_finished_write(vnmp);
		CTR2(KTR_VFS,
		    "%s: impossible to recycle, %p is already referenced",
		    __func__, vp);
		return (EBUSY);
	}
	if (!VN_IS_DOOMED(vp)) {
		counter_u64_add(recycles_free_count, 1);
		vgonel(vp);
	}
	VOP_UNLOCK(vp);
	vdropl(vp);
	vn_finished_write(vnmp);
	return (0);
}

/*
 * Allocate a new vnode.