/*      $NetBSD: uvm_page_array.c,v 1.9 2020/05/26 21:52:12 ad Exp $    */

/*-
* Copyright (c)2011 YAMAMOTO Takashi,
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uvm_page_array.c,v 1.9 2020/05/26 21:52:12 ad Exp $");

#include <sys/param.h>
#include <sys/systm.h>

#include <uvm/uvm_extern.h>
#include <uvm/uvm_object.h>
#include <uvm/uvm_page.h>
#include <uvm/uvm_page_array.h>

/*
* uvm_page_array_init: initialize the array.
*/

void
uvm_page_array_init(struct uvm_page_array *ar, struct uvm_object *uobj,
   unsigned int flags)
{

       ar->ar_idx = 0;
       ar->ar_npages = 0;
       ar->ar_uobj = uobj;
       ar->ar_flags = flags;
}

/*
* uvm_page_array_fini: clean up the array.
*/

void
uvm_page_array_fini(struct uvm_page_array *ar)
{

       /*
        * currently nothing to do.
        */
#if defined(DIAGNOSTIC)
       /*
        * poison to trigger assertion in uvm_page_array_peek to
        * detect usage errors.
        */
       ar->ar_npages = 1;
       ar->ar_idx = 1000;
#endif /* defined(DIAGNOSTIC) */
}

/*
* uvm_page_array_clear: forget the cached pages and initialize the array.
*/

void
uvm_page_array_clear(struct uvm_page_array *ar)
{

       KASSERT(ar->ar_idx <= ar->ar_npages);
       ar->ar_idx = 0;
       ar->ar_npages = 0;
}

/*
* uvm_page_array_peek: return the next cached page.
*/

struct vm_page *
uvm_page_array_peek(struct uvm_page_array *ar)
{

       KASSERT(ar->ar_idx <= ar->ar_npages);
       if (ar->ar_idx == ar->ar_npages) {
               return NULL;
       }
       return ar->ar_pages[ar->ar_idx];
}

/*
* uvm_page_array_advance: advance the array to the next cached page
*/

void
uvm_page_array_advance(struct uvm_page_array *ar)
{

       KASSERT(ar->ar_idx <= ar->ar_npages);
       ar->ar_idx++;
       KASSERT(ar->ar_idx <= ar->ar_npages);
}

/*
* uvm_page_array_fill: lookup pages and keep them cached.
*
* return 0 on success.  in that case, cache the result in the array
* so that they will be picked by later uvm_page_array_peek.
*
* nwant is a number of pages to fetch.  a caller should consider it a hint.
* nwant == 0 means a caller have no specific idea.
*
* return ENOENT if no pages are found.
*
* called with object lock held.
*/

int
uvm_page_array_fill(struct uvm_page_array *ar, voff_t off, unsigned int nwant)
{
       unsigned int npages;
#if defined(DEBUG)
       unsigned int i;
#endif /* defined(DEBUG) */
       unsigned int maxpages = __arraycount(ar->ar_pages);
       struct uvm_object *uobj = ar->ar_uobj;
       const int flags = ar->ar_flags;
       const bool dense = (flags & UVM_PAGE_ARRAY_FILL_DENSE) != 0;
       const bool backward = (flags & UVM_PAGE_ARRAY_FILL_BACKWARD) != 0;
       int error = 0;

       if (nwant != 0 && nwant < maxpages) {
               maxpages = nwant;
       }
#if 0 /* called from DDB for "show obj/f" without lock */
       KASSERT(rw_lock_held(uobj->vmobjlock));
#endif
       KASSERT(uvm_page_array_peek(ar) == NULL);
       if ((flags & UVM_PAGE_ARRAY_FILL_DIRTY) != 0) {
               unsigned int tagmask = UVM_PAGE_DIRTY_TAG;

               if ((flags & UVM_PAGE_ARRAY_FILL_WRITEBACK) != 0) {
                       tagmask |= UVM_PAGE_WRITEBACK_TAG;
               }
               npages =
                   (backward ? radix_tree_gang_lookup_tagged_node_reverse :
                   radix_tree_gang_lookup_tagged_node)(
                   &uobj->uo_pages, off >> PAGE_SHIFT, (void **)ar->ar_pages,
                   maxpages, dense, tagmask);
       } else {
               npages =
                   (backward ? radix_tree_gang_lookup_node_reverse :
                   radix_tree_gang_lookup_node)(
                   &uobj->uo_pages, off >> PAGE_SHIFT, (void **)ar->ar_pages,
                   maxpages, dense);
       }
       if (npages == 0) {
               if (flags != 0) {
                       /*
                        * if dense or looking for tagged entries (or
                        * working backwards), fail right away.
                        */
                       npages = 0;
               } else {
                       /*
                        * there's nothing else to be found with the current
                        * set of arguments, in the current version of the
                        * tree.
                        *
                        * minimize repeated tree lookups by "finding" a
                        * null pointer, in case the caller keeps looping (a
                        * common use case).
                        */
                       npages = 1;
                       ar->ar_pages[0] = NULL;
               }
               error = ENOENT;
       }
       KASSERT(npages <= maxpages);
       ar->ar_npages = npages;
       ar->ar_idx = 0;
#if defined(DEBUG)
       for (i = 0; error == 0 && i < ar->ar_npages; i++) {
               struct vm_page * const pg = ar->ar_pages[i];

               KASSERT(pg != NULL);
               KDASSERT(pg->uobject == uobj);
               if (backward) {
                       KDASSERT(pg->offset <= off);
                       KDASSERT(i == 0 ||
                           pg->offset < ar->ar_pages[i - 1]->offset);
               } else {
                       KDASSERT(pg->offset >= off);
                       KDASSERT(i == 0 ||
                           pg->offset > ar->ar_pages[i - 1]->offset);
               }
       }
#endif /* defined(DEBUG) */
       return error;
}

/*
* uvm_page_array_fill_and_peek:
* same as uvm_page_array_peek except that, if the array is empty, try to fill
* it first.
*/

struct vm_page *
uvm_page_array_fill_and_peek(struct uvm_page_array *ar, voff_t off,
   unsigned int nwant)
{
       int error;

       if (ar->ar_idx != ar->ar_npages) {
               return ar->ar_pages[ar->ar_idx];
       }
       error = uvm_page_array_fill(ar, off, nwant);
       if (error != 0) {
               return NULL;
       }
       return uvm_page_array_peek(ar);
}

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