kernel: vm: Add objects, page struct and pagers

This commit expands the virtual memory subsystem by providing the
initial implementation of virtual memory objects, pager descriptors and
pagers. This change currently implemenents a minimal vnode pager.

Signed-off-by: Ian Moffett <ian@osmora.org>

9 files changed, 609 insertions, 0 deletions

diff --git a/sys/include/sys/vnode.h b/sys/include/sys/vnode.h
index d9f9afe..dfa6a30 100644
--- a/sys/include/sys/vnode.h
+++ b/sys/include/sys/vnode.h
@@ -34,6 +34,7 @@
 #include <sys/queue.h>
 #include <sys/atomic.h>
 #include <sys/sio.h>
+#include <vm/vm_obj.h>
 
 #if defined(_KERNEL)
 
@@ -44,6 +45,7 @@ struct vnode {
     int flags;
     void *data;
     const struct vops *vops;
+    struct vm_object vobj;
     uint32_t refcount;
     TAILQ_ENTRY(vnode) vcache_link;
 };
diff --git a/sys/include/vm/vm_obj.h b/sys/include/vm/vm_obj.h
new file mode 100644
index 0000000..78a7dbb
--- /dev/null
+++ b/sys/include/vm/vm_obj.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#ifndef _VM_OBJ_H_
+#define _VM_OBJ_H_
+
+#include <sys/types.h>
+#include <sys/queue.h>
+#include <sys/spinlock.h>
+#include <sys/cdefs.h>
+#include <vm/vm_pager.h>
+#include <vm/vm_page.h>
+#include <vm/vm.h>
+
+struct vm_object {
+    struct spinlock lock;
+    const struct vm_pagerops *pgops;
+    RBT_HEAD(vm_objtree, vm_page) objt;
+    vm_prot_t prot;
+    void *data;
+    int refs;
+    int npages;
+};
+
+int vm_obj_init(struct vm_object *obp, const struct vm_pagerops *pgops, int refs);
+void vm_obj_release(struct vm_object *obp);
+
+/* Object tree stuff */
+int vm_pagecmp(const struct vm_page *a, const struct vm_page *b);
+RBT_PROTOTYPE(vm_objtree, vm_page, objt, vm_pagecmp)
+
+#endif  /* !_VM_OBJ_H_ */
diff --git a/sys/include/vm/vm_page.h b/sys/include/vm/vm_page.h
new file mode 100644
index 0000000..665431c
--- /dev/null
+++ b/sys/include/vm/vm_page.h
@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#ifndef _VM_PAGE_H_
+#define _VM_PAGE_H_
+
+#include <sys/types.h>
+#include <sys/tree.h>
+#include <sys/queue.h>
+#include <sys/param.h>
+#include <sys/spinlock.h>
+
+struct vm_object;
+
+/*
+ * Represents a single virtual memory page.
+ */
+struct vm_page {
+    TAILQ_ENTRY(vm_page) pageq;     /* Queue data */
+    RBT_ENTRY(vm_page) objt;        /* Object tree */
+    paddr_t phys_addr;              /* Physical address of page */
+    struct spinlock lock;           /* Page lock */
+    uint32_t flags;                 /* Page flags */
+    off_t offset;                   /* Offset into object */
+};
+
+/* Page flags */
+#define PG_VALID    BIT(0)      /* Has to be set to be valid */
+#define PG_CLEAN    BIT(1)      /* Page has not be written to */
+#define PG_REQ      BIT(2)      /* Page has been requested by someone */
+
+/* Page alloc flags */
+#define PALLOC_ZERO BIT(0)
+
+struct vm_page *vm_pagelookup(struct vm_object *obj, off_t off);
+struct vm_page *vm_pagealloc(struct vm_object *obj, int flags);
+void vm_pagefree(struct vm_object *obj, struct vm_page *pg, int flags);
+
+#endif  /* !_VM_PAGE_H_ */
diff --git a/sys/include/vm/vm_pager.h b/sys/include/vm/vm_pager.h
new file mode 100644
index 0000000..80a5a6c
--- /dev/null
+++ b/sys/include/vm/vm_pager.h
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#ifndef _VM_PAGER_H_
+#define _VM_PAGER_H_
+
+#include <sys/types.h>
+#include <vm/vm_page.h>
+#include <vm/vm_obj.h>
+
+struct vm_object;
+
+/*
+ * Pager operations.
+ *
+ * @init: Init pager
+ * @get: Read a page.
+ * @put: Write a page.
+ */
+struct vm_pagerops {
+    void(*init)(void);
+    int(*get)(struct vm_object *obp, struct vm_page **pgs, off_t off, size_t len);
+    int(*put)(struct vm_object *obp, struct vm_page *pgs, size_t len);
+};
+
+int vm_pager_get(struct vm_object *obp, struct vm_page **pgs, off_t off, size_t len);
+
+#endif  /* !_VM_PAGER_H_ */
diff --git a/sys/include/vm/vm_vnode.h b/sys/include/vm/vm_vnode.h
new file mode 100644
index 0000000..138cfe2
--- /dev/null
+++ b/sys/include/vm/vm_vnode.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#ifndef _VM_VNODE_H_
+#define _VM_VNODE_H_
+
+#include <sys/types.h>
+#include <sys/vnode.h>
+#include <vm/vm_pager.h>
+#include <vm/vm_obj.h>
+#include <vm/pmap.h>
+
+extern const struct vm_pagerops vm_vnops;
+
+struct vm_object *vn_attach(struct vnode *vp, vm_prot_t prot);
+
+#endif  /* !_VM_VNODE_H_ */
diff --git a/sys/vm/vm_obj.c b/sys/vm/vm_obj.c
new file mode 100644
index 0000000..75545dc
--- /dev/null
+++ b/sys/vm/vm_obj.c
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#include <vm/vm_obj.h>
+#include <vm/vm_pager.h>
+
+int
+vm_obj_init(struct vm_object *obp, const struct vm_pagerops *pgops, int refs)
+{
+    if (obp == NULL || pgops == NULL)
+        return -1;
+
+    obp->pgops = pgops;
+    obp->refs = refs;
+    obp->npages = 0;
+    RBT_INIT(vm_objtree, &obp->objt);
+    return 0;
+}
+
+void
+vm_obj_release(struct vm_object *obp)
+{
+    /* STUB */
+    (void)obp;
+}
diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
new file mode 100644
index 0000000..8ada183
--- /dev/null
+++ b/sys/vm/vm_page.c
@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#include <vm/vm_page.h>
+#include <vm/vm_obj.h>
+#include <vm/physmem.h>
+#include <vm/dynalloc.h>
+#include <vm/vm.h>
+#include <assert.h>
+#include <string.h>
+
+RBT_GENERATE(vm_objtree, vm_page, objt, vm_pagecmp);
+
+/*
+ * Insert a page into an object.
+ */
+static inline void
+vm_pageinsert(struct vm_page *pg, struct vm_object *obp)
+{
+   struct vm_page *tmp;
+
+   tmp = RBT_INSERT(vm_objtree, &obp->objt, pg);
+   __assert(tmp == NULL);
+   ++obp->npages;
+}
+
+static inline void
+vm_pageremove(struct vm_page *pg, struct vm_object *obp)
+{
+    RBT_REMOVE(vm_objtree, &obp->objt, pg);
+    --obp->npages;
+}
+
+struct vm_page *
+vm_pagelookup(struct vm_object *obj, off_t off)
+{
+    struct vm_page tmp;
+
+    tmp.offset = off;
+    return RBT_FIND(vm_objtree, &obj->objt, &tmp);
+}
+
+struct vm_page *
+vm_pagealloc(struct vm_object *obj, int flags)
+{
+    struct vm_page *tmp;
+
+    tmp = dynalloc(sizeof(*tmp));
+    if (tmp == NULL) {
+        return NULL;
+    }
+
+    memset(tmp, 0, sizeof(*tmp));
+    tmp->phys_addr = vm_alloc_frame(1);
+    tmp->flags |= (PG_VALID | PG_CLEAN);
+    __assert(tmp->phys_addr != 0);
+
+    if (ISSET(flags, PALLOC_ZERO)) {
+        memset(PHYS_TO_VIRT(tmp->phys_addr), 0, DEFAULT_PAGESIZE);
+    }
+
+    vm_pageinsert(tmp, obj);
+    return tmp;
+}
+
+void
+vm_pagefree(struct vm_object *obj, struct vm_page *pg, int flags)
+{
+    __assert(pg->phys_addr != 0);
+
+    vm_pageremove(pg, obj);
+    vm_free_frame(pg->phys_addr, 1);
+    dynfree(pg);
+}
+
+int
+vm_pagecmp(const struct vm_page *a, const struct vm_page *b)
+{
+    return (a->offset < b->offset) ? -1 : a->offset > b->offset;
+}
diff --git a/sys/vm/vm_pager.c b/sys/vm/vm_pager.c
new file mode 100644
index 0000000..2a85d55
--- /dev/null
+++ b/sys/vm/vm_pager.c
@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#include <sys/types.h>
+#include <sys/errno.h>
+#include <vm/vm_pager.h>
+#include <vm/vm_obj.h>
+
+int
+vm_pager_get(struct vm_object *obp, struct vm_page **pgs, off_t off, size_t len)
+{
+    const struct vm_pagerops *pgops = obp->pgops;
+
+    if (pgops->get == NULL) {
+        return -ENOTSUP;
+    }
+
+    return pgops->get(obp, pgs, off, len);
+}
diff --git a/sys/vm/vm_vnode.c b/sys/vm/vm_vnode.c
new file mode 100644
index 0000000..31e74cc
--- /dev/null
+++ b/sys/vm/vm_vnode.c
@@ -0,0 +1,185 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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.
+ * 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 Hyra 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#include <sys/types.h>
+#include <sys/cdefs.h>
+#include <sys/errno.h>
+#include <sys/syslog.h>
+#include <sys/systm.h>
+#include <sys/vnode.h>
+#include <vm/vm_vnode.h>
+#include <vm/vm_page.h>
+#include <vm/pmap.h>
+#include <vm/vm.h>
+
+#define VN_TIMEOUT_USEC 200000
+
+#define pr_trace(fmt, ...) kprintf("vm_vnode: " fmt, ##__VA_ARGS__)
+#define pr_error(...) pr_trace(__VA_ARGS__)
+
+/* Debug print helper */
+#if defined(PR_DEBUG)
+#define pr_debug(...) pr_trace(__VA_ARGS__)
+#else
+#define pr_debug(...) __nothing
+#endif  /* PR_DEBUG */
+
+const struct vm_pagerops vm_vnops;
+
+/*
+ * Perform read/write operation on vnode to/from pages.
+ *
+ * Returns number of bytes read.
+ */
+static int
+vn_io(struct vnode *vp, struct vm_page **pgs, unsigned int npages, int rw)
+{
+    struct vop_getattr_args args;
+    struct sio_txn sio;
+    struct vattr vattr;
+    size_t c, read = 0;
+    int err;
+
+    /* TODO: Add support for writes */
+    if (rw != 0) {
+        return -ENOTSUP;
+    }
+
+    args.vp = vp;
+    args.res = &vattr;
+    c = MAX(vattr.size / DEFAULT_PAGESIZE, 1);
+
+    if ((err = vfs_vop_getattr(vp, &args)) != 0) {
+        return err;
+    }
+
+    if (npages > c) {
+        npages = c;
+    }
+
+    /* Prepare SIO constants */
+    sio.len = DEFAULT_PAGESIZE;
+    sio.offset = 0;
+
+    /* Copy in each page */
+    for (size_t i = 0; i < npages; ++i) {
+        sio.buf = PHYS_TO_VIRT(pgs[i]->phys_addr);
+        read = vfs_vop_read(vp, &sio);
+        if (read < 0)
+            pr_debug("vn_io: page-in @ %p failed (err=%d)\n", err);
+    }
+
+    return read;
+}
+
+/*
+ * Get pages from backing store.
+ *
+ * @obp: Object representing the backing store.
+ * @pgs: Page descriptors to be filled.
+ * @off: Offset to read from in backing store.
+ * @len: Length to read in bytes.
+ */
+static int
+vn_get(struct vm_object *obp, struct vm_page **pgs, off_t off, size_t len)
+{
+    struct vm_page *pgtmp;
+    size_t j, pgcnt;
+
+    spinlock_acquire(&obp->lock);
+
+    for (int i = off; i < len; i += DEFAULT_PAGESIZE) {
+        j = i / DEFAULT_PAGESIZE;
+        pgtmp = vm_pagelookup(obp, i);
+
+        /*
+         * If we have no corresponding page in the object
+         * at this offset, we will need to make our own.
+         */
+        if (pgtmp == NULL) {
+            pgtmp = vm_pagealloc(obp, PALLOC_ZERO);
+            if (pgtmp == NULL) {
+                pgs[j]->flags &= ~PG_VALID;
+                continue;
+            }
+            pgtmp->offset = i;
+            pgs[j] = pgtmp;
+        }
+
+        if (spinlock_usleep(&pgtmp->lock, VN_TIMEOUT_USEC) != 0) {
+            pgs[j]->flags &= ~PG_VALID;
+            continue;
+        }
+
+        /* Set the page count and ensure it is valid */
+        pgcnt = ALIGN_DOWN(len, DEFAULT_PAGESIZE);
+        pgcnt = MAX(pgcnt, 1);
+
+        /* Page in and save this pgtmp */
+        vn_io(obp->data, &pgtmp, pgcnt, 0);
+        pgs[j] = pgtmp;
+        spinlock_release(&pgtmp->lock);
+    }
+
+    spinlock_release(&obp->lock);
+    return 0;
+}
+
+/*
+ * Attach a virtual memory object to a vnode.
+ *
+ * @vp: Vnode to attach to.
+ */
+struct vm_object *
+vn_attach(struct vnode *vp, vm_prot_t prot)
+{
+    struct vm_object *vmobj;
+    int error;
+
+    if (vp->type != VREG) {
+        pr_error("vn_attach: vp=%p, prot=%x\n", vp, prot);
+        pr_error("vn_attach: Special files not supported yet!\n");
+        return NULL;
+    }
+
+    error = vm_obj_init(&vp->vobj, &vm_vnops, 1);
+    if (error != 0) {
+        return NULL;
+    }
+
+    vmobj = &vp->vobj;
+    vmobj->prot = prot;
+    vmobj->data = vp;
+    vmobj->pgops = &vm_vnops;
+    return vmobj;
+}
+
+const struct vm_pagerops vm_vnops = {
+    .get = vn_get
+};