/*
 * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
 * Copyright (c) 2010 David Chinner.
 * Copyright (c) 2011 Christoph Hellwig.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_types.h"
#include "xfs_log.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc.h"
#include "xfs_inode.h"
#include "xfs_extent_busy.h"
#include "xfs_trace.h"

void
xfs_extent_busy_insert(
        struct xfs_trans        *tp,
        xfs_agnumber_t          agno,
        xfs_agblock_t           bno,
        xfs_extlen_t            len,
        unsigned int            flags)
{
        struct xfs_extent_busy  *new;
        struct xfs_extent_busy  *busyp;
        struct xfs_perag        *pag;
        struct rb_node          **rbp;
        struct rb_node          *parent = NULL;

        new = kmem_zalloc(sizeof(struct xfs_extent_busy), KM_MAYFAIL);
        if (!new) {
                /*
                 * No Memory!  Since it is now not possible to track the free
                 * block, make this a synchronous transaction to insure that
                 * the block is not reused before this transaction commits.
                 */
                trace_xfs_extent_busy_enomem(tp->t_mountp, agno, bno, len);
                xfs_trans_set_sync(tp);
                return;
        }

        new->agno = agno;
        new->bno = bno;
        new->length = len;
        INIT_LIST_HEAD(&new->list);
        new->flags = flags;

        /* trace before insert to be able to see failed inserts */
        trace_xfs_extent_busy(tp->t_mountp, agno, bno, len);

        pag = xfs_perag_get(tp->t_mountp, new->agno);
        spin_lock(&pag->pagb_lock);
        rbp = &pag->pagb_tree.rb_node;
        while (*rbp) {
                parent = *rbp;
                busyp = rb_entry(parent, struct xfs_extent_busy, rb_node);

                if (new->bno < busyp->bno) {
                        rbp = &(*rbp)->rb_left;
                        ASSERT(new->bno + new->length <= busyp->bno);
                } else if (new->bno > busyp->bno) {
                        rbp = &(*rbp)->rb_right;
                        ASSERT(bno >= busyp->bno + busyp->length);
                } else {
                        ASSERT(0);
                }
        }

        rb_link_node(&new->rb_node, parent, rbp);
        rb_insert_color(&new->rb_node, &pag->pagb_tree);

        list_add(&new->list, &tp->t_busy);
        spin_unlock(&pag->pagb_lock);
        xfs_perag_put(pag);
}

/*
 * Search for a busy extent within the range of the extent we are about to
 * allocate.  You need to be holding the busy extent tree lock when calling
 * xfs_extent_busy_search(). This function returns 0 for no overlapping busy
 * extent, -1 for an overlapping but not exact busy extent, and 1 for an exact
 * match. This is done so that a non-zero return indicates an overlap that
 * will require a synchronous transaction, but it can still be
 * used to distinguish between a partial or exact match.
 */
int
xfs_extent_busy_search(
        struct xfs_mount        *mp,
        xfs_agnumber_t          agno,
        xfs_agblock_t           bno,
        xfs_extlen_t            len)
{
        struct xfs_perag        *pag;
        struct rb_node          *rbp;
        struct xfs_extent_busy  *busyp;
        int                     match = 0;

        pag = xfs_perag_get(mp, agno);
        spin_lock(&pag->pagb_lock);

        rbp = pag->pagb_tree.rb_node;

        /* find closest start bno overlap */
        while (rbp) {
                busyp = rb_entry(rbp, struct xfs_extent_busy, rb_node);
                if (bno < busyp->bno) {
                        /* may overlap, but exact start block is lower */
                        if (bno + len > busyp->bno)
                                match = -1;
                        rbp = rbp->rb_left;
                } else if (bno > busyp->bno) {
                        /* may overlap, but exact start block is higher */
                        if (bno < busyp->bno + busyp->length)
                                match = -1;
                        rbp = rbp->rb_right;
                } else {
                        /* bno matches busyp, length determines exact match */
                        match = (busyp->length == len) ? 1 : -1;
                        break;
                }
        }
        spin_unlock(&pag->pagb_lock);
        xfs_perag_put(pag);
        return match;
}

/*
 * The found free extent [fbno, fend] overlaps part or all of the given busy
 * extent.  If the overlap covers the beginning, the end, or all of the busy
 * extent, the overlapping portion can be made unbusy and used for the
 * allocation.  We can't split a busy extent because we can't modify a
 * transaction/CIL context busy list, but we can update an entries block
 * number or length.
 *
 * Returns true if the extent can safely be reused, or false if the search
 * needs to be restarted.
 */
STATIC bool
xfs_extent_busy_update_extent(
        struct xfs_mount        *mp,
        struct xfs_perag        *pag,
        struct xfs_extent_busy  *busyp,
        xfs_agblock_t           fbno,
        xfs_extlen_t            flen,
        bool                    userdata)
{
        xfs_agblock_t           fend = fbno + flen;
        xfs_agblock_t           bbno = busyp->bno;
        xfs_agblock_t           bend = bbno + busyp->length;

        /*
         * This extent is currently being discarded.  Give the thread
         * performing the discard a chance to mark the extent unbusy
         * and retry.
         */
        if (busyp->flags & XFS_EXTENT_BUSY_DISCARDED) {
                spin_unlock(&pag->pagb_lock);
                delay(1);
                spin_lock(&pag->pagb_lock);
                return false;
        }

        /*
         * If there is a busy extent overlapping a user allocation, we have
         * no choice but to force the log and retry the search.
         *
         * Fortunately this does not happen during normal operation, but
         * only if the filesystem is very low on space and has to dip into
         * the AGFL for normal allocations.
         */
        if (userdata)
                goto out_force_log;

        if (bbno < fbno && bend > fend) {
                /*
                 * Case 1:
                 *    bbno           bend
                 *    +BBBBBBBBBBBBBBBBB+
                 *        +---------+
                 *        fbno   fend
                 */

                /*
                 * We would have to split the busy extent to be able to track
                 * it correct, which we cannot do because we would have to
                 * modify the list of busy extents attached to the transaction
                 * or CIL context, which is immutable.
                 *
                 * Force out the log to clear the busy extent and retry the
                 * search.
                 */
                goto out_force_log;
        } else if (bbno >= fbno && bend <= fend) {
                /*
                 * Case 2:
                 *    bbno           bend
                 *    +BBBBBBBBBBBBBBBBB+
                 *    +-----------------+
                 *    fbno           fend
                 *
                 * Case 3:
                 *    bbno           bend
                 *    +BBBBBBBBBBBBBBBBB+
                 *    +--------------------------+
                 *    fbno                    fend
                 *
                 * Case 4:
                 *             bbno           bend
                 *             +BBBBBBBBBBBBBBBBB+
                 *    +--------------------------+
                 *    fbno                    fend
                 *
                 * Case 5:
                 *             bbno           bend
                 *             +BBBBBBBBBBBBBBBBB+
                 *    +-----------------------------------+
                 *    fbno                             fend
                 *
                 */

                /*
                 * The busy extent is fully covered by the extent we are
                 * allocating, and can simply be removed from the rbtree.
                 * However we cannot remove it from the immutable list
                 * tracking busy extents in the transaction or CIL context,
                 * so set the length to zero to mark it invalid.
                 *
                 * We also need to restart the busy extent search from the
                 * tree root, because erasing the node can rearrange the
                 * tree topology.
                 */
                rb_erase(&busyp->rb_node, &pag->pagb_tree);
                busyp->length = 0;
                return false;
        } else if (fend < bend) {
                /*
                 * Case 6:
                 *              bbno           bend
                 *             +BBBBBBBBBBBBBBBBB+
                 *             +---------+
                 *             fbno   fend
                 *
                 * Case 7:
                 *             bbno           bend
                 *             +BBBBBBBBBBBBBBBBB+
                 *    +------------------+
                 *    fbno            fend
                 *
                 */
                busyp->bno = fend;
        } else if (bbno < fbno) {
                /*
                 * Case 8:
                 *    bbno           bend
                 *    +BBBBBBBBBBBBBBBBB+
                 *        +-------------+
                 *        fbno       fend
                 *
                 * Case 9:
                 *    bbno           bend
                 *    +BBBBBBBBBBBBBBBBB+
                 *        +----------------------+
                 *        fbno                fend
                 */
                busyp->length = fbno - busyp->bno;
        } else {
                ASSERT(0);
        }

        trace_xfs_extent_busy_reuse(mp, pag->pag_agno, fbno, flen);
        return true;

out_force_log:
        spin_unlock(&pag->pagb_lock);
        xfs_log_force(mp, XFS_LOG_SYNC);
        trace_xfs_extent_busy_force(mp, pag->pag_agno, fbno, flen);
        spin_lock(&pag->pagb_lock);
        return false;
}


/*
 * For a given extent [fbno, flen], make sure we can reuse it safely.
 */
void
xfs_extent_busy_reuse(
        struct xfs_mount        *mp,
        xfs_agnumber_t          agno,
        xfs_agblock_t           fbno,
        xfs_extlen_t            flen,
        bool                    userdata)
{
        struct xfs_perag        *pag;
        struct rb_node          *rbp;

        ASSERT(flen > 0);

        pag = xfs_perag_get(mp, agno);
        spin_lock(&pag->pagb_lock);
restart:
        rbp = pag->pagb_tree.rb_node;
        while (rbp) {
                struct xfs_extent_busy *busyp =
                        rb_entry(rbp, struct xfs_extent_busy, rb_node);
                xfs_agblock_t   bbno = busyp->bno;
                xfs_agblock_t   bend = bbno + busyp->length;

                if (fbno + flen <= bbno) {
                        rbp = rbp->rb_left;
                        continue;
                } else if (fbno >= bend) {
                        rbp = rbp->rb_right;
                        continue;
                }

                if (!xfs_extent_busy_update_extent(mp, pag, busyp, fbno, flen,
                                                  userdata))
                        goto restart;
        }
        spin_unlock(&pag->pagb_lock);
        xfs_perag_put(pag);
}

/*
 * For a given extent [fbno, flen], search the busy extent list to find a
 * subset of the extent that is not busy.  If *rlen is smaller than
 * args->minlen no suitable extent could be found, and the higher level
 * code needs to force out the log and retry the allocation.
 */
void
xfs_extent_busy_trim(
        struct xfs_alloc_arg    *args,
        xfs_agblock_t           bno,
        xfs_extlen_t            len,
        xfs_agblock_t           *rbno,
        xfs_extlen_t            *rlen)
{
        xfs_agblock_t           fbno;
        xfs_extlen_t            flen;
        struct rb_node          *rbp;

        ASSERT(len > 0);

        spin_lock(&args->pag->pagb_lock);
restart:
        fbno = bno;
        flen = len;
        rbp = args->pag->pagb_tree.rb_node;
        while (rbp && flen >= args->minlen) {
                struct xfs_extent_busy *busyp =
                        rb_entry(rbp, struct xfs_extent_busy, rb_node);
                xfs_agblock_t   fend = fbno + flen;
                xfs_agblock_t   bbno = busyp->bno;
                xfs_agblock_t   bend = bbno + busyp->length;

                if (fend <= bbno) {
                        rbp = rbp->rb_left;
                        continue;
                } else if (fbno >= bend) {
                        rbp = rbp->rb_right;
                        continue;
                }

                /*
                 * If this is a metadata allocation, try to reuse the busy
                 * extent instead of trimming the allocation.
                 */
                if (!args->userdata &&
                    !(busyp->flags & XFS_EXTENT_BUSY_DISCARDED)) {
                        if (!xfs_extent_busy_update_extent(args->mp, args->pag,
                                                          busyp, fbno, flen,
                                                          false))
                                goto restart;
                        continue;
                }

                if (bbno <= fbno) {
                        /* start overlap */

                        /*
                         * Case 1:
                         *    bbno           bend
                         *    +BBBBBBBBBBBBBBBBB+
                         *        +---------+
                         *        fbno   fend
                         *
                         * Case 2:
                         *    bbno           bend
                         *    +BBBBBBBBBBBBBBBBB+
                         *    +-------------+
                         *    fbno       fend
                         *
                         * Case 3:
                         *    bbno           bend
                         *    +BBBBBBBBBBBBBBBBB+
                         *        +-------------+
                         *        fbno       fend
                         *
                         * Case 4:
                         *    bbno           bend
                         *    +BBBBBBBBBBBBBBBBB+
                         *    +-----------------+
                         *    fbno           fend
                         *
                         * No unbusy region in extent, return failure.
                         */
                        if (fend <= bend)
                                goto fail;

                        /*
                         * Case 5:
                         *    bbno           bend
                         *    +BBBBBBBBBBBBBBBBB+
                         *        +----------------------+
                         *        fbno                fend
                         *
                         * Case 6:
                         *    bbno           bend
                         *    +BBBBBBBBBBBBBBBBB+
                         *    +--------------------------+
                         *    fbno                    fend
                         *
                         * Needs to be trimmed to:
                         *                       +-------+
                         *                       fbno fend
                         */
                        fbno = bend;
                } else if (bend >= fend) {
                        /* end overlap */

                        /*
                         * Case 7:
                         *             bbno           bend
                         *             +BBBBBBBBBBBBBBBBB+
                         *    +------------------+
                         *    fbno            fend
                         *
                         * Case 8:
                         *             bbno           bend
                         *             +BBBBBBBBBBBBBBBBB+
                         *    +--------------------------+
                         *    fbno                    fend
                         *
                         * Needs to be trimmed to:
                         *    +-------+
                         *    fbno fend
                         */
                        fend = bbno;
                } else {
                        /* middle overlap */

                        /*
                         * Case 9:
                         *             bbno           bend
                         *             +BBBBBBBBBBBBBBBBB+
                         *    +-----------------------------------+
                         *    fbno                             fend
                         *
                         * Can be trimmed to:
                         *    +-------+        OR         +-------+
                         *    fbno fend                   fbno fend
                         *
                         * Backward allocation leads to significant
                         * fragmentation of directories, which degrades
                         * directory performance, therefore we always want to
                         * choose the option that produces forward allocation
                         * patterns.
                         * Preferring the lower bno extent will make the next
                         * request use "fend" as the start of the next
                         * allocation;  if the segment is no longer busy at
                         * that point, we'll get a contiguous allocation, but
                         * even if it is still busy, we will get a forward
                         * allocation.
                         * We try to avoid choosing the segment at "bend",
                         * because that can lead to the next allocation
                         * taking the segment at "fbno", which would be a
                         * backward allocation.  We only use the segment at
                         * "fbno" if it is much larger than the current
                         * requested size, because in that case there's a
                         * good chance subsequent allocations will be
                         * contiguous.
                         */
                        if (bbno - fbno >= args->maxlen) {
                                /* left candidate fits perfect */
                                fend = bbno;
                        } else if (fend - bend >= args->maxlen * 4) {
                                /* right candidate has enough free space */
                                fbno = bend;
                        } else if (bbno - fbno >= args->minlen) {
                                /* left candidate fits minimum requirement */
                                fend = bbno;
                        } else {
                                goto fail;
                        }
                }

                flen = fend - fbno;
        }
        spin_unlock(&args->pag->pagb_lock);

        if (fbno != bno || flen != len) {
                trace_xfs_extent_busy_trim(args->mp, args->agno, bno, len,
                                          fbno, flen);
        }
        *rbno = fbno;
        *rlen = flen;
        return;
fail:
        /*
         * Return a zero extent length as failure indications.  All callers
         * re-check if the trimmed extent satisfies the minlen requirement.
         */
        spin_unlock(&args->pag->pagb_lock);
        trace_xfs_extent_busy_trim(args->mp, args->agno, bno, len, fbno, 0);
        *rbno = fbno;
        *rlen = 0;
}

STATIC void
xfs_extent_busy_clear_one(
        struct xfs_mount        *mp,
        struct xfs_perag        *pag,
        struct xfs_extent_busy  *busyp)
{
        if (busyp->length) {
                trace_xfs_extent_busy_clear(mp, busyp->agno, busyp->bno,
                                                busyp->length);
                rb_erase(&busyp->rb_node, &pag->pagb_tree);
        }

        list_del_init(&busyp->list);
        kmem_free(busyp);
}

/*
 * Remove all extents on the passed in list from the busy extents tree.
 * If do_discard is set skip extents that need to be discarded, and mark
 * these as undergoing a discard operation instead.
 */
void
xfs_extent_busy_clear(
        struct xfs_mount        *mp,
        struct list_head        *list,
        bool                    do_discard)
{
        struct xfs_extent_busy  *busyp, *n;
        struct xfs_perag        *pag = NULL;
        xfs_agnumber_t          agno = NULLAGNUMBER;

        list_for_each_entry_safe(busyp, n, list, list) {
                if (busyp->agno != agno) {
                        if (pag) {
                                spin_unlock(&pag->pagb_lock);
                                xfs_perag_put(pag);
                        }
                        pag = xfs_perag_get(mp, busyp->agno);
                        spin_lock(&pag->pagb_lock);
                        agno = busyp->agno;
                }

                if (do_discard && busyp->length &&
                    !(busyp->flags & XFS_EXTENT_BUSY_SKIP_DISCARD))
                        busyp->flags = XFS_EXTENT_BUSY_DISCARDED;
                else
                        xfs_extent_busy_clear_one(mp, pag, busyp);
        }

        if (pag) {
                spin_unlock(&pag->pagb_lock);
                xfs_perag_put(pag);
        }
}

/*
 * Callback for list_sort to sort busy extents by the AG they reside in.
 */
int
xfs_extent_busy_ag_cmp(
        void                    *priv,
        struct list_head        *a,
        struct list_head        *b)
{
        return container_of(a, struct xfs_extent_busy, list)->agno -
                container_of(b, struct xfs_extent_busy, list)->agno;
}