vm: fix a null dereference on out-of-memory

[minix.git] / sys / ufs / lfs / lfs_bio.c

/*      $NetBSD: lfs_bio.c,v 1.120 2011/07/11 08:27:40 hannken Exp $    */

/*-
 * Copyright (c) 1999, 2000, 2001, 2002, 2003, 2008 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Konrad E. Schroder <perseant@hhhh.org>.
 *
 * 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */
/*
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  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 the University 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 REGENTS 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 REGENTS 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.
 *
 *      @(#)lfs_bio.c   8.10 (Berkeley) 6/10/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: lfs_bio.c,v 1.120 2011/07/11 08:27:40 hannken Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/resourcevar.h>
#include <sys/mount.h>
#include <sys/kernel.h>
#include <sys/kauth.h>

#include <ufs/ufs/inode.h>
#include <ufs/ufs/ufsmount.h>
#include <ufs/ufs/ufs_extern.h>

#include <ufs/lfs/lfs.h>
#include <ufs/lfs/lfs_extern.h>

#include <uvm/uvm.h>

/*
 * LFS block write function.
 *
 * XXX
 * No write cost accounting is done.
 * This is almost certainly wrong for synchronous operations and NFS.
 *
 * protected by lfs_lock.
 */
int     locked_queue_count   = 0;       /* Count of locked-down buffers. */
long    locked_queue_bytes   = 0L;      /* Total size of locked buffers. */
int     lfs_subsys_pages     = 0L;      /* Total number LFS-written pages */
int     lfs_fs_pagetrip      = 0;       /* # of pages to trip per-fs write */
int     lfs_writing          = 0;       /* Set if already kicked off a writer
                                           because of buffer space */

/* Lock and condition variables for above. */
kcondvar_t      locked_queue_cv;
kcondvar_t      lfs_writing_cv;
kmutex_t        lfs_lock;

extern int lfs_dostats;

/*
 * reserved number/bytes of locked buffers
 */
int locked_queue_rcount = 0;
long locked_queue_rbytes = 0L;

static int lfs_fits_buf(struct lfs *, int, int);
static int lfs_reservebuf(struct lfs *, struct vnode *vp, struct vnode *vp2,
    int, int);
static int lfs_reserveavail(struct lfs *, struct vnode *vp, struct vnode *vp2,
    int);

static int
lfs_fits_buf(struct lfs *fs, int n, int bytes)
{
        int count_fit, bytes_fit;

        ASSERT_NO_SEGLOCK(fs);
        KASSERT(mutex_owned(&lfs_lock));

        count_fit =
            (locked_queue_count + locked_queue_rcount + n <= LFS_WAIT_BUFS);
        bytes_fit =
            (locked_queue_bytes + locked_queue_rbytes + bytes <= LFS_WAIT_BYTES);

#ifdef DEBUG
        if (!count_fit) {
                DLOG((DLOG_AVAIL, "lfs_fits_buf: no fit count: %d + %d + %d >= %d\n",
                      locked_queue_count, locked_queue_rcount,
                      n, LFS_WAIT_BUFS));
        }
        if (!bytes_fit) {
                DLOG((DLOG_AVAIL, "lfs_fits_buf: no fit bytes: %ld + %ld + %d >= %ld\n",
                      locked_queue_bytes, locked_queue_rbytes,
                      bytes, LFS_WAIT_BYTES));
        }
#endif /* DEBUG */

        return (count_fit && bytes_fit);
}

/* ARGSUSED */
static int
lfs_reservebuf(struct lfs *fs, struct vnode *vp,
    struct vnode *vp2, int n, int bytes)
{
        ASSERT_MAYBE_SEGLOCK(fs);
        KASSERT(locked_queue_rcount >= 0);
        KASSERT(locked_queue_rbytes >= 0);

        mutex_enter(&lfs_lock);
        while (n > 0 && !lfs_fits_buf(fs, n, bytes)) {
                int error;

                lfs_flush(fs, 0, 0);

                error = cv_timedwait_sig(&locked_queue_cv, &lfs_lock,
                    hz * LFS_BUFWAIT);
                if (error && error != EWOULDBLOCK) {
                        mutex_exit(&lfs_lock);
                        return error;
                }
        }

        locked_queue_rcount += n;
        locked_queue_rbytes += bytes;

        if (n < 0)
                cv_broadcast(&locked_queue_cv);

        mutex_exit(&lfs_lock);

        KASSERT(locked_queue_rcount >= 0);
        KASSERT(locked_queue_rbytes >= 0);

        return 0;
}

/*
 * Try to reserve some blocks, prior to performing a sensitive operation that
 * requires the vnode lock to be honored.  If there is not enough space, give
 * up the vnode lock temporarily and wait for the space to become available.
 *
 * Called with vp locked.  (Note nowever that if fsb < 0, vp is ignored.)
 *
 * XXX YAMT - it isn't safe to unlock vp here
 * because the node might be modified while we sleep.
 * (eg. cached states like i_offset might be stale,
 *  the vnode might be truncated, etc..)
 * maybe we should have a way to restart the vnodeop (EVOPRESTART?)
 * or rearrange vnodeop interface to leave vnode locking to file system
 * specific code so that each file systems can have their own vnode locking and
 * vnode re-using strategies.
 */
static int
lfs_reserveavail(struct lfs *fs, struct vnode *vp,
    struct vnode *vp2, int fsb)
{
        CLEANERINFO *cip;
        struct buf *bp;
        int error, slept;

        ASSERT_MAYBE_SEGLOCK(fs);
        slept = 0;
        mutex_enter(&lfs_lock);
        while (fsb > 0 && !lfs_fits(fs, fsb + fs->lfs_ravail + fs->lfs_favail)) {
                mutex_exit(&lfs_lock);
#if 0
                /*
                 * XXX ideally, we should unlock vnodes here
                 * because we might sleep very long time.
                 */
                VOP_UNLOCK(vp);
                if (vp2 != NULL) {
                        VOP_UNLOCK(vp2);
                }
#else
                /*
                 * XXX since we'll sleep for cleaner with vnode lock holding,
                 * deadlock will occur if cleaner tries to lock the vnode.
                 * (eg. lfs_markv -> lfs_fastvget -> getnewvnode -> vclean)
                 */
#endif

                if (!slept) {
                        DLOG((DLOG_AVAIL, "lfs_reserve: waiting for %ld (bfree = %d,"
                              " est_bfree = %d)\n",
                              fsb + fs->lfs_ravail + fs->lfs_favail,
                              fs->lfs_bfree, LFS_EST_BFREE(fs)));
                }
                ++slept;

                /* Wake up the cleaner */
                LFS_CLEANERINFO(cip, fs, bp);
                LFS_SYNC_CLEANERINFO(cip, fs, bp, 0);
                lfs_wakeup_cleaner(fs);

                mutex_enter(&lfs_lock);
                /* Cleaner might have run while we were reading, check again */
                if (lfs_fits(fs, fsb + fs->lfs_ravail + fs->lfs_favail))
                        break;

                error = mtsleep(&fs->lfs_avail, PCATCH | PUSER, "lfs_reserve",
                                0, &lfs_lock);
#if 0
                vn_lock(vp, LK_EXCLUSIVE | LK_RETRY); /* XXX use lockstatus */
                vn_lock(vp2, LK_EXCLUSIVE | LK_RETRY); /* XXX use lockstatus */
#endif
                if (error) {
                        mutex_exit(&lfs_lock);
                        return error;
                }
        }
#ifdef DEBUG
        if (slept) {
                DLOG((DLOG_AVAIL, "lfs_reserve: woke up\n"));
        }
#endif
        fs->lfs_ravail += fsb;
        mutex_exit(&lfs_lock);

        return 0;
}

#ifdef DIAGNOSTIC
int lfs_rescount;
int lfs_rescountdirop;
#endif

int
lfs_reserve(struct lfs *fs, struct vnode *vp, struct vnode *vp2, int fsb)
{
        int error;
        int cantwait;

        ASSERT_MAYBE_SEGLOCK(fs);
        if (vp2) {
                /* Make sure we're not in the process of reclaiming vp2 */
                mutex_enter(&lfs_lock);
                while(fs->lfs_flags & LFS_UNDIROP) {
                        mtsleep(&fs->lfs_flags, PRIBIO + 1, "lfsrundirop", 0,
                            &lfs_lock);
                }
                mutex_exit(&lfs_lock);
        }

        KASSERT(fsb < 0 || VOP_ISLOCKED(vp));
        KASSERT(vp2 == NULL || fsb < 0 || VOP_ISLOCKED(vp2));
        KASSERT(vp2 == NULL || !(VTOI(vp2)->i_flag & IN_ADIROP));
        KASSERT(vp2 == NULL || vp2 != fs->lfs_unlockvp);

        cantwait = (VTOI(vp)->i_flag & IN_ADIROP) || fs->lfs_unlockvp == vp;
#ifdef DIAGNOSTIC
        if (cantwait) {
                if (fsb > 0)
                        lfs_rescountdirop++;
                else if (fsb < 0)
                        lfs_rescountdirop--;
                if (lfs_rescountdirop < 0)
                        panic("lfs_rescountdirop");
        }
        else {
                if (fsb > 0)
                        lfs_rescount++;
                else if (fsb < 0)
                        lfs_rescount--;
                if (lfs_rescount < 0)
                        panic("lfs_rescount");
        }
#endif
        if (cantwait)
                return 0;

        /*
         * XXX
         * vref vnodes here so that cleaner doesn't try to reuse them.
         * (see XXX comment in lfs_reserveavail)
         */
        vhold(vp);
        if (vp2 != NULL) {
                vhold(vp2);
        }

        error = lfs_reserveavail(fs, vp, vp2, fsb);
        if (error)
                goto done;

        /*
         * XXX just a guess. should be more precise.
         */
        error = lfs_reservebuf(fs, vp, vp2, fsb, fsbtob(fs, fsb));
        if (error)
                lfs_reserveavail(fs, vp, vp2, -fsb);

done:
        holdrele(vp);
        if (vp2 != NULL) {
                holdrele(vp2);
        }

        return error;
}

int
lfs_bwrite(void *v)
{
        struct vop_bwrite_args /* {
                struct vnode *a_vp;
                struct buf *a_bp;
        } */ *ap = v;
        struct buf *bp = ap->a_bp;

#ifdef DIAGNOSTIC
        if (VTOI(bp->b_vp)->i_lfs->lfs_ronly == 0 && (bp->b_flags & B_ASYNC)) {
                panic("bawrite LFS buffer");
        }
#endif /* DIAGNOSTIC */
        return lfs_bwrite_ext(bp, 0);
}

/*
 * Determine if there is enough room currently available to write fsb
 * blocks.  We need enough blocks for the new blocks, the current
 * inode blocks (including potentially the ifile inode), a summary block,
 * and the segment usage table, plus an ifile block.
 */
int
lfs_fits(struct lfs *fs, int fsb)
{
        int needed;

        ASSERT_NO_SEGLOCK(fs);
        needed = fsb + btofsb(fs, fs->lfs_sumsize) +
                 ((howmany(fs->lfs_uinodes + 1, INOPB(fs)) + fs->lfs_segtabsz +
                   1) << (fs->lfs_bshift - fs->lfs_ffshift));

        if (needed >= fs->lfs_avail) {
#ifdef DEBUG
                DLOG((DLOG_AVAIL, "lfs_fits: no fit: fsb = %ld, uinodes = %ld, "
                      "needed = %ld, avail = %ld\n",
                      (long)fsb, (long)fs->lfs_uinodes, (long)needed,
                      (long)fs->lfs_avail));
#endif
                return 0;
        }
        return 1;
}

int
lfs_availwait(struct lfs *fs, int fsb)
{
        int error;
        CLEANERINFO *cip;
        struct buf *cbp;

        ASSERT_NO_SEGLOCK(fs);
        /* Push cleaner blocks through regardless */
        mutex_enter(&lfs_lock);
        if (LFS_SEGLOCK_HELD(fs) &&
            fs->lfs_sp->seg_flags & (SEGM_CLEAN | SEGM_FORCE_CKP)) {
                mutex_exit(&lfs_lock);
                return 0;
        }
        mutex_exit(&lfs_lock);

        while (!lfs_fits(fs, fsb)) {
                /*
                 * Out of space, need cleaner to run.
                 * Update the cleaner info, then wake it up.
                 * Note the cleanerinfo block is on the ifile
                 * so it CANT_WAIT.
                 */
                LFS_CLEANERINFO(cip, fs, cbp);
                LFS_SYNC_CLEANERINFO(cip, fs, cbp, 0);

#ifdef DEBUG
                DLOG((DLOG_AVAIL, "lfs_availwait: out of available space, "
                      "waiting on cleaner\n"));
#endif

                lfs_wakeup_cleaner(fs);
#ifdef DIAGNOSTIC
                if (LFS_SEGLOCK_HELD(fs))
                        panic("lfs_availwait: deadlock");
#endif
                error = tsleep(&fs->lfs_avail, PCATCH | PUSER, "cleaner", 0);
                if (error)
                        return (error);
        }
        return 0;
}

int
lfs_bwrite_ext(struct buf *bp, int flags)
{
        struct lfs *fs;
        struct inode *ip;
        struct vnode *vp;
        int fsb;

        vp = bp->b_vp;
        fs = VFSTOUFS(vp->v_mount)->um_lfs;

        ASSERT_MAYBE_SEGLOCK(fs);
        KASSERT(bp->b_cflags & BC_BUSY);
        KASSERT(flags & BW_CLEAN || !LFS_IS_MALLOC_BUF(bp));
        KASSERT(((bp->b_oflags | bp->b_flags) & (BO_DELWRI|B_LOCKED))
            != BO_DELWRI);

        /*
         * Don't write *any* blocks if we're mounted read-only, or
         * if we are "already unmounted".
         *
         * In particular the cleaner can't write blocks either.
         */
        if (fs->lfs_ronly || (fs->lfs_pflags & LFS_PF_CLEAN)) {
                bp->b_oflags &= ~BO_DELWRI;
                bp->b_flags |= B_READ;
                bp->b_error = 0;
                mutex_enter(&bufcache_lock);
                LFS_UNLOCK_BUF(bp);
                if (LFS_IS_MALLOC_BUF(bp))
                        bp->b_cflags &= ~BC_BUSY;
                else
                        brelsel(bp, 0);
                mutex_exit(&bufcache_lock);
                return (fs->lfs_ronly ? EROFS : 0);
        }

        /*
         * Set the delayed write flag and use reassignbuf to move the buffer
         * from the clean list to the dirty one.
         *
         * Set the B_LOCKED flag and unlock the buffer, causing brelse to move
         * the buffer onto the LOCKED free list.  This is necessary, otherwise
         * getnewbuf() would try to reclaim the buffers using bawrite, which
         * isn't going to work.
         *
         * XXX we don't let meta-data writes run out of space because they can
         * come from the segment writer.  We need to make sure that there is
         * enough space reserved so that there's room to write meta-data
         * blocks.
         */
        if ((bp->b_flags & B_LOCKED) == 0) {
                fsb = numfrags(fs, bp->b_bcount);

                ip = VTOI(vp);
                mutex_enter(&lfs_lock);
                if (flags & BW_CLEAN) {
                        LFS_SET_UINO(ip, IN_CLEANING);
                } else {
                        LFS_SET_UINO(ip, IN_MODIFIED);
                }
                mutex_exit(&lfs_lock);
                fs->lfs_avail -= fsb;

                mutex_enter(&bufcache_lock);
                mutex_enter(vp->v_interlock);
                bp->b_oflags = (bp->b_oflags | BO_DELWRI) & ~BO_DONE;
                LFS_LOCK_BUF(bp);
                bp->b_flags &= ~B_READ;
                bp->b_error = 0;
                reassignbuf(bp, bp->b_vp);
                mutex_exit(vp->v_interlock);
        } else {
                mutex_enter(&bufcache_lock);
        }

        if (bp->b_iodone != NULL)
                bp->b_cflags &= ~BC_BUSY;
        else
                brelsel(bp, 0);
        mutex_exit(&bufcache_lock);

        return (0);
}

/*
 * Called and return with the lfs_lock held.
 */
void
lfs_flush_fs(struct lfs *fs, int flags)
{
        ASSERT_NO_SEGLOCK(fs);
        KASSERT(mutex_owned(&lfs_lock));
        if (fs->lfs_ronly)
                return;

        if (lfs_dostats)
                ++lfs_stats.flush_invoked;

        mutex_exit(&lfs_lock);
        lfs_writer_enter(fs, "fldirop");
        lfs_segwrite(fs->lfs_ivnode->v_mount, flags);
        lfs_writer_leave(fs);
        mutex_enter(&lfs_lock);
        fs->lfs_favail = 0; /* XXX */
}

/*
 * This routine initiates segment writes when LFS is consuming too many
 * resources.  Ideally the pageout daemon would be able to direct LFS
 * more subtly.
 * XXX We have one static count of locked buffers;
 * XXX need to think more about the multiple filesystem case.
 *
 * Called and return with lfs_lock held.
 * If fs != NULL, we hold the segment lock for fs.
 */
void
lfs_flush(struct lfs *fs, int flags, int only_onefs)
{
        extern u_int64_t locked_fakequeue_count;
        struct mount *mp, *nmp;
        struct lfs *tfs;

        KASSERT(mutex_owned(&lfs_lock));
        KDASSERT(fs == NULL || !LFS_SEGLOCK_HELD(fs));

        if (lfs_dostats)
                ++lfs_stats.write_exceeded;
        /* XXX should we include SEGM_CKP here? */
        if (lfs_writing && !(flags & SEGM_SYNC)) {
                DLOG((DLOG_FLUSH, "lfs_flush: not flushing because another flush is active\n"));
                return;
        }
        while (lfs_writing)
                cv_wait(&lfs_writing_cv, &lfs_lock);
        lfs_writing = 1;

        mutex_exit(&lfs_lock);

        if (only_onefs) {
                KASSERT(fs != NULL);
                if (vfs_busy(fs->lfs_ivnode->v_mount, NULL))
                        goto errout;
                mutex_enter(&lfs_lock);
                lfs_flush_fs(fs, flags);
                mutex_exit(&lfs_lock);
                vfs_unbusy(fs->lfs_ivnode->v_mount, false, NULL);
        } else {
                locked_fakequeue_count = 0;
                mutex_enter(&mountlist_lock);
                for (mp = CIRCLEQ_FIRST(&mountlist); mp != (void *)&mountlist;
                     mp = nmp) {
                        if (vfs_busy(mp, &nmp)) {
                                DLOG((DLOG_FLUSH, "lfs_flush: fs vfs_busy\n"));
                                continue;
                        }
                        if (strncmp(&mp->mnt_stat.f_fstypename[0], MOUNT_LFS,
                            sizeof(mp->mnt_stat.f_fstypename)) == 0) {
                                tfs = VFSTOUFS(mp)->um_lfs;
                                mutex_enter(&lfs_lock);
                                lfs_flush_fs(tfs, flags);
                                mutex_exit(&lfs_lock);
                        }
                        vfs_unbusy(mp, false, &nmp);
                }
                mutex_exit(&mountlist_lock);
        }
        LFS_DEBUG_COUNTLOCKED("flush");
        wakeup(&lfs_subsys_pages);

    errout:
        mutex_enter(&lfs_lock);
        KASSERT(lfs_writing);
        lfs_writing = 0;
        wakeup(&lfs_writing);
}

#define INOCOUNT(fs) howmany((fs)->lfs_uinodes, INOPB(fs))
#define INOBYTES(fs) ((fs)->lfs_uinodes * sizeof (struct ufs1_dinode))

/*
 * make sure that we don't have too many locked buffers.
 * flush buffers if needed.
 */
int
lfs_check(struct vnode *vp, daddr_t blkno, int flags)
{
        int error;
        struct lfs *fs;
        struct inode *ip;
        extern pid_t lfs_writer_daemon;

        error = 0;
        ip = VTOI(vp);

        /* If out of buffers, wait on writer */
        /* XXX KS - if it's the Ifile, we're probably the cleaner! */
        if (ip->i_number == LFS_IFILE_INUM)
                return 0;
        /* If we're being called from inside a dirop, don't sleep */
        if (ip->i_flag & IN_ADIROP)
                return 0;

        fs = ip->i_lfs;

        ASSERT_NO_SEGLOCK(fs);

        /*
         * If we would flush below, but dirops are active, sleep.
         * Note that a dirop cannot ever reach this code!
         */
        mutex_enter(&lfs_lock);
        while (fs->lfs_dirops > 0 &&
               (locked_queue_count + INOCOUNT(fs) > LFS_MAX_BUFS ||
                locked_queue_bytes + INOBYTES(fs) > LFS_MAX_BYTES ||
                lfs_subsys_pages > LFS_MAX_PAGES ||
                fs->lfs_dirvcount > LFS_MAX_FSDIROP(fs) ||
                lfs_dirvcount > LFS_MAX_DIROP || fs->lfs_diropwait > 0))
        {
                ++fs->lfs_diropwait;
                mtsleep(&fs->lfs_writer, PRIBIO+1, "bufdirop", 0,
                        &lfs_lock);
                --fs->lfs_diropwait;
        }

#ifdef DEBUG
        if (locked_queue_count + INOCOUNT(fs) > LFS_MAX_BUFS)
                DLOG((DLOG_FLUSH, "lfs_check: lqc = %d, max %d\n",
                      locked_queue_count + INOCOUNT(fs), LFS_MAX_BUFS));
        if (locked_queue_bytes + INOBYTES(fs) > LFS_MAX_BYTES)
                DLOG((DLOG_FLUSH, "lfs_check: lqb = %ld, max %ld\n",
                      locked_queue_bytes + INOBYTES(fs), LFS_MAX_BYTES));
        if (lfs_subsys_pages > LFS_MAX_PAGES)
                DLOG((DLOG_FLUSH, "lfs_check: lssp = %d, max %d\n",
                      lfs_subsys_pages, LFS_MAX_PAGES));
        if (lfs_fs_pagetrip && fs->lfs_pages > lfs_fs_pagetrip)
                DLOG((DLOG_FLUSH, "lfs_check: fssp = %d, trip at %d\n",
                      fs->lfs_pages, lfs_fs_pagetrip));
        if (lfs_dirvcount > LFS_MAX_DIROP)
                DLOG((DLOG_FLUSH, "lfs_check: ldvc = %d, max %d\n",
                      lfs_dirvcount, LFS_MAX_DIROP));
        if (fs->lfs_dirvcount > LFS_MAX_FSDIROP(fs))
                DLOG((DLOG_FLUSH, "lfs_check: lfdvc = %d, max %d\n",
                      fs->lfs_dirvcount, LFS_MAX_FSDIROP(fs)));
        if (fs->lfs_diropwait > 0)
                DLOG((DLOG_FLUSH, "lfs_check: ldvw = %d\n",
                      fs->lfs_diropwait));
#endif

        /* If there are too many pending dirops, we have to flush them. */
        if (fs->lfs_dirvcount > LFS_MAX_FSDIROP(fs) ||
            lfs_dirvcount > LFS_MAX_DIROP || fs->lfs_diropwait > 0) {
                flags |= SEGM_CKP;
        }

        if (locked_queue_count + INOCOUNT(fs) > LFS_MAX_BUFS ||
            locked_queue_bytes + INOBYTES(fs) > LFS_MAX_BYTES ||
            lfs_subsys_pages > LFS_MAX_PAGES ||
            fs->lfs_dirvcount > LFS_MAX_FSDIROP(fs) ||
            lfs_dirvcount > LFS_MAX_DIROP || fs->lfs_diropwait > 0) {
                lfs_flush(fs, flags, 0);
        } else if (lfs_fs_pagetrip && fs->lfs_pages > lfs_fs_pagetrip) {
                /*
                 * If we didn't flush the whole thing, some filesystems
                 * still might want to be flushed.
                 */
                ++fs->lfs_pdflush;
                wakeup(&lfs_writer_daemon);
        }

        while (locked_queue_count + INOCOUNT(fs) >= LFS_WAIT_BUFS ||
                locked_queue_bytes + INOBYTES(fs) >= LFS_WAIT_BYTES ||
                lfs_subsys_pages > LFS_WAIT_PAGES ||
                fs->lfs_dirvcount > LFS_MAX_FSDIROP(fs) ||
                lfs_dirvcount > LFS_MAX_DIROP) {

                if (lfs_dostats)
                        ++lfs_stats.wait_exceeded;
                DLOG((DLOG_AVAIL, "lfs_check: waiting: count=%d, bytes=%ld\n",
                      locked_queue_count, locked_queue_bytes));
                error = cv_timedwait_sig(&locked_queue_cv, &lfs_lock,
                    hz * LFS_BUFWAIT);
                if (error != EWOULDBLOCK)
                        break;

                /*
                 * lfs_flush might not flush all the buffers, if some of the
                 * inodes were locked or if most of them were Ifile blocks
                 * and we weren't asked to checkpoint.  Try flushing again
                 * to keep us from blocking indefinitely.
                 */
                if (locked_queue_count + INOCOUNT(fs) >= LFS_MAX_BUFS ||
                    locked_queue_bytes + INOBYTES(fs) >= LFS_MAX_BYTES) {
                        lfs_flush(fs, flags | SEGM_CKP, 0);
                }
        }
        mutex_exit(&lfs_lock);
        return (error);
}

/*
 * Allocate a new buffer header.
 */
struct buf *
lfs_newbuf(struct lfs *fs, struct vnode *vp, daddr_t daddr, size_t size, int type)
{
        struct buf *bp;
        size_t nbytes;

        ASSERT_MAYBE_SEGLOCK(fs);
        nbytes = roundup(size, fsbtob(fs, 1));

        bp = getiobuf(NULL, true);
        if (nbytes) {
                bp->b_data = lfs_malloc(fs, nbytes, type);
                /* memset(bp->b_data, 0, nbytes); */
        }
#ifdef DIAGNOSTIC
        if (vp == NULL)
                panic("vp is NULL in lfs_newbuf");
        if (bp == NULL)
                panic("bp is NULL after malloc in lfs_newbuf");
#endif

        bp->b_bufsize = size;
        bp->b_bcount = size;
        bp->b_lblkno = daddr;
        bp->b_blkno = daddr;
        bp->b_error = 0;
        bp->b_resid = 0;
        bp->b_iodone = lfs_callback;
        bp->b_cflags = BC_BUSY | BC_NOCACHE;
        bp->b_private = fs;

        mutex_enter(&bufcache_lock);
        mutex_enter(vp->v_interlock);
        bgetvp(vp, bp);
        mutex_exit(vp->v_interlock);
        mutex_exit(&bufcache_lock);

        return (bp);
}

void
lfs_freebuf(struct lfs *fs, struct buf *bp)
{
        struct vnode *vp;

        if ((vp = bp->b_vp) != NULL) {
                mutex_enter(&bufcache_lock);
                mutex_enter(vp->v_interlock);
                brelvp(bp);
                mutex_exit(vp->v_interlock);
                mutex_exit(&bufcache_lock);
        }
        if (!(bp->b_cflags & BC_INVAL)) { /* BC_INVAL indicates a "fake" buffer */
                lfs_free(fs, bp->b_data, LFS_NB_UNKNOWN);
                bp->b_data = NULL;
        }
        putiobuf(bp);
}

/*
 * Count buffers on the "locked" queue, and compare it to a pro-forma count.
 * Don't count malloced buffers, since they don't detract from the total.
 */
void
lfs_countlocked(int *count, long *bytes, const char *msg)
{
        struct buf *bp;
        int n = 0;
        long int size = 0L;

        mutex_enter(&bufcache_lock);
        TAILQ_FOREACH(bp, &bufqueues[BQ_LOCKED].bq_queue, b_freelist) {
                KASSERT(bp->b_iodone == NULL);
                n++;
                size += bp->b_bufsize;
#ifdef DIAGNOSTIC
                if (n > nbuf)
                        panic("lfs_countlocked: this can't happen: more"
                              " buffers locked than exist");
#endif
        }
        /*
         * Theoretically this function never really does anything.
         * Give a warning if we have to fix the accounting.
         */
        if (n != *count) {
                DLOG((DLOG_LLIST, "lfs_countlocked: %s: adjusted buf count"
                      " from %d to %d\n", msg, *count, n));
        }
        if (size != *bytes) {
                DLOG((DLOG_LLIST, "lfs_countlocked: %s: adjusted byte count"
                      " from %ld to %ld\n", msg, *bytes, size));
        }
        *count = n;
        *bytes = size;
        mutex_exit(&bufcache_lock);
        return;
}

int
lfs_wait_pages(void)
{
        int active, inactive;

        uvm_estimatepageable(&active, &inactive);
        return LFS_WAIT_RESOURCE(active + inactive + uvmexp.free, 1);
}

int
lfs_max_pages(void)
{
        int active, inactive;

        uvm_estimatepageable(&active, &inactive);
        return LFS_MAX_RESOURCE(active + inactive + uvmexp.free, 1);
}