drop net-snmp dep

[unleashed.git] / kernel / fs / dcfs / dc_vnops.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2017 by Delphix. All rights reserved.
 */

/*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
/*        All Rights Reserved   */

/*
 * University Copyright- Copyright (c) 1982, 1986, 1988
 * The Regents of the University of California
 * All Rights Reserved
 *
 * University Acknowledgment- Portions of this document are derived from
 * software developed by the University of California, Berkeley, and its
 * contributors.
 */

#include <sys/types.h>
#include <sys/thread.h>
#include <sys/t_lock.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bitmap.h>
#include <sys/buf.h>
#include <sys/cmn_err.h>
#include <sys/conf.h>
#include <sys/ddi.h>
#include <sys/debug.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/fcntl.h>
#include <sys/flock.h>
#include <sys/file.h>
#include <sys/kmem.h>
#include <sys/mman.h>
#include <sys/vmsystm.h>
#include <sys/open.h>
#include <sys/swap.h>
#include <sys/sysmacros.h>
#include <sys/uio.h>
#include <sys/vfs.h>
#include <sys/vnode.h>
#include <sys/stat.h>
#include <sys/poll.h>
#include <sys/zmod.h>
#include <sys/fs/decomp.h>

#include <vm/hat.h>
#include <vm/as.h>
#include <vm/page.h>
#include <vm/pvn.h>
#include <vm/seg_vn.h>
#include <vm/seg_kmem.h>
#include <vm/seg_map.h>

#include <sys/fs_subr.h>

/*
 * dcfs - A filesystem for automatic decompressing of fiocompressed files
 *
 * This filesystem is a layered filesystem that sits on top of a normal
 * persistent filesystem and provides automatic decompression of files
 * that have been previously compressed and stored on the host file system.
 * This is a pseudo filesystem in that it does not persist data, rather it
 * intercepts file lookup requests on the host filesystem and provides
 * transparent decompression of those files. Currently the only supported
 * host filesystem is ufs.
 *
 * A file is compressed via a userland utility (currently cmd/boot/fiocompress)
 * and marked by fiocompress as a compressed file via a flag in the on-disk
 * inode (set via a ufs ioctl() - see `ufs_vnops.c`ufs_ioctl()`_FIO_COMPRESSED
 * ufs_lookup checks for this flag and if set, passes control to decompvp
 * a function defined in this (dcfs) filesystem. decomvp uncompresses the file
 * and returns a dcfs vnode to the VFS layer.
 *
 * dcfs is layered on top of ufs and passes requests involving persistence
 * to the underlying ufs filesystem. The compressed files currently cannot be
 * written to.
 */


/*
 * Define data structures within this file.
 */
#define DCSHFT          5
#define DCTABLESIZE     16

#if ((DCTABLESIZE & (DCTABLESIZE - 1)) == 0)
#define DCHASH(vp) (((uintptr_t)(vp) >> DCSHFT) & (DCTABLESIZE - 1))
#else
#define DCHASH(vp) (((uintptr_t)(vp) >> DCSHFT) % DTABLESIZEC)
#endif

#define DCLRUSIZE       16

#define DCCACHESIZE     4

#define rounddown(x, y) ((x) & ~((y) - 1))

struct dcnode   *dctable[DCTABLESIZE];

struct dcnode   *dclru;
static int      dclru_len;

kmutex_t        dctable_lock;

dev_t           dcdev;
struct vfs      dc_vfs;

struct kmem_cache *dcnode_cache;
struct kmem_cache *dcbuf_cache[DCCACHESIZE];

kmutex_t        dccache_lock;

static int dcinit(int, char *);

static struct dcnode    *dcnode_alloc(void);
static void             dcnode_free(struct dcnode *);
static void             dcnode_recycle(struct dcnode *);

static void             dcinsert(struct dcnode *);
static void             dcdelete(struct dcnode *);
static struct dcnode    *dcfind(struct vnode *);
static void             dclru_add(struct dcnode *);
static void             dclru_sub(struct dcnode *);


/*
 * This is the loadable module wrapper.
 */
#include <sys/modctl.h>

/* yes, we want all defaults */
static const struct vfsops dc_vfsops;

static vfsdef_t vfw = {
        VFSDEF_VERSION,
        "dcfs",
        dcinit,
        VSW_ZMOUNT,
        NULL
};

/*
 * Module linkage information for the kernel.
 */
extern struct mod_ops mod_fsops;

static struct modlfs modlfs = {
        &mod_fsops, "compressed filesystem", &vfw
};

static struct modlinkage modlinkage = {
        MODREV_1, (void *)&modlfs, NULL
};

int
_init()
{
        return (mod_install(&modlinkage));
}

int
_info(struct modinfo *modinfop)
{
        return (mod_info(&modlinkage, modinfop));
}


static int dc_open(struct vnode **, int, struct cred *, caller_context_t *);
static int dc_close(struct vnode *, int, int, offset_t,
    struct cred *, caller_context_t *);
static int dc_read(struct vnode *, struct uio *, int, struct cred *,
    struct caller_context *);
static int dc_getattr(struct vnode *, struct vattr *, int,
    struct cred *, caller_context_t *);
static int dc_setattr(struct vnode *, struct vattr *, int, struct cred *,
    struct caller_context *);
static int dc_access(struct vnode *, int, int,
    struct cred *, caller_context_t *);
static int dc_fsync(struct vnode *, int, struct cred *, caller_context_t *);
static void dc_inactive(struct vnode *, struct cred *, caller_context_t *);
static int dc_fid(struct vnode *, struct fid *, caller_context_t *);
static int dc_seek(struct vnode *, offset_t, offset_t *, caller_context_t *);
static int dc_frlock(struct vnode *, int, struct flock64 *, int, offset_t,
    struct flk_callback *, struct cred *, caller_context_t *);
static int dc_realvp(struct vnode *, struct vnode **, caller_context_t *);
static int dc_getpage(struct vnode *, offset_t, size_t, uint_t *,
    struct page **, size_t, struct seg *, caddr_t, enum seg_rw,
    struct cred *, caller_context_t *);
static int dc_putpage(struct vnode *, offset_t, size_t, int,
    struct cred *, caller_context_t *);
static int dc_map(struct vnode *, offset_t, struct as *, caddr_t *, size_t,
    uchar_t, uchar_t, uint_t, struct cred *, caller_context_t *);
static int dc_addmap(struct vnode *, offset_t, struct as *, caddr_t, size_t,
    uchar_t, uchar_t, uint_t, struct cred *, caller_context_t *);
static int dc_delmap(struct vnode *, offset_t, struct as *, caddr_t, size_t,
    uint_t, uint_t, uint_t, struct cred *, caller_context_t *);

static const struct vnodeops dc_vnodeops = {
        .vnop_name = "dcfs",
        .vop_open = dc_open,
        .vop_close = dc_close,
        .vop_read = dc_read,
        .vop_getattr =  dc_getattr,
        .vop_setattr = dc_setattr,
        .vop_access = dc_access,
        .vop_fsync = dc_fsync,
        .vop_inactive = dc_inactive,
        .vop_fid = dc_fid,
        .vop_seek = dc_seek,
        .vop_frlock = dc_frlock,
        .vop_realvp = dc_realvp,
        .vop_getpage = dc_getpage,
        .vop_putpage = dc_putpage,
        .vop_map = dc_map,
        .vop_addmap = dc_addmap,
        .vop_delmap = dc_delmap,
};

/*ARGSUSED*/
static int
dc_open(struct vnode **vpp, int flag, struct cred *cr, caller_context_t *ctp)
{
        return (0);
}

/*ARGSUSED*/
static int
dc_close(struct vnode *vp, int flag, int count, offset_t off,
    struct cred *cr, caller_context_t *ctp)
{
        (void) cleanlocks(vp, ttoproc(curthread)->p_pid, 0);
        cleanshares(vp, ttoproc(curthread)->p_pid);
        return (0);
}

/*ARGSUSED*/
static int
dc_read(struct vnode *vp, struct uio *uiop, int ioflag, struct cred *cr,
    struct caller_context *ct)
{
        struct dcnode *dp = VTODC(vp);
        size_t rdsize = MAX(MAXBSIZE, dp->dc_hdr->ch_blksize);
        size_t fsize = dp->dc_hdr->ch_fsize;
        int error;

        /*
         * Loop through file with segmap, decompression will occur
         * in dc_getapage
         */
        do {
                caddr_t base;
                size_t n;
                offset_t mapon;

                /*
                 * read to end of block or file
                 */
                mapon = uiop->uio_loffset & (rdsize - 1);
                n = MIN(rdsize - mapon, uiop->uio_resid);
                n = MIN(n, fsize - uiop->uio_loffset);
                if (n == 0)
                        return (0);     /* at EOF */

                base = segmap_getmapflt(segkmap, vp, uiop->uio_loffset, n, 1,
                    S_READ);
                error = uiomove(base + mapon, n, UIO_READ, uiop);
                if (!error) {
                        uint_t flags;

                        if (n + mapon == rdsize || uiop->uio_loffset == fsize)
                                flags = SM_DONTNEED;
                        else
                                flags = 0;
                        error = segmap_release(segkmap, base, flags);
                } else
                        (void) segmap_release(segkmap, base, 0);
        } while (!error && uiop->uio_resid);

        return (error);
}

static int
dc_getattr(struct vnode *vp, struct vattr *vap, int flags,
    cred_t *cred, caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);
        struct vnode *subvp = dp->dc_subvp;
        int error;

        error = fop_getattr(subvp, vap, flags, cred, ctp);

        /* substitute uncompressed size */
        vap->va_size = dp->dc_hdr->ch_fsize;
        return (error);
}

static int
dc_setattr(struct vnode *vp, struct vattr *vap, int flags, cred_t *cred,
    caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);
        struct vnode *subvp = dp->dc_subvp;

        return (fop_setattr(subvp, vap, flags, cred, ctp));
}

static int
dc_access(struct vnode *vp, int mode, int flags,
    cred_t *cred, caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);
        struct vnode *subvp = dp->dc_subvp;

        return (fop_access(subvp, mode, flags, cred, ctp));
}

/*ARGSUSED*/
static int
dc_fsync(vnode_t *vp, int syncflag, cred_t *cred, caller_context_t *ctp)
{
        return (0);
}

/*ARGSUSED*/
static void
dc_inactive(struct vnode *vp, cred_t *cr, caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);

        mutex_enter(&dctable_lock);
        mutex_enter(&vp->v_lock);
        ASSERT(vp->v_count >= 1);
        VN_RELE_LOCKED(vp);
        if (vp->v_count != 0) {
                /*
                 * Somebody accessed the dcnode before we got a chance to
                 * remove it.  They will remove it when they do a vn_rele.
                 */
                mutex_exit(&vp->v_lock);
                mutex_exit(&dctable_lock);
                return;
        }
        mutex_exit(&vp->v_lock);

        dcnode_free(dp);

        mutex_exit(&dctable_lock);
}

static int
dc_fid(struct vnode *vp, struct fid *fidp, caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);
        struct vnode *subvp = dp->dc_subvp;

        return (fop_fid(subvp, fidp, ctp));
}

static int
dc_seek(struct vnode *vp, offset_t oof, offset_t *noffp, caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);
        struct vnode *subvp = dp->dc_subvp;

        return (fop_seek(subvp, oof, noffp, ctp));
}

static int
dc_frlock(struct vnode *vp, int cmd, struct flock64 *bfp, int flag,
    offset_t offset, struct flk_callback *flk_cbp,
    cred_t *cr, caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);
        int error;
        struct vattr vattr;

        /*
         * If file is being mapped, disallow frlock.
         */
        vattr.va_mask = VATTR_MODE;
        if (error = fop_getattr(dp->dc_subvp, &vattr, 0, cr, ctp))
                return (error);
        if (dp->dc_mapcnt > 0 && MANDLOCK(vp, vattr.va_mode))
                return (EAGAIN);

        return (fs_frlock(vp, cmd, bfp, flag, offset, flk_cbp, cr, ctp));
}

/*ARGSUSED*/
static int
dc_getblock_miss(struct vnode *vp, offset_t off, size_t len, struct page **ppp,
    struct seg *seg, caddr_t addr, enum seg_rw rw, struct cred *cr)
{
        struct dcnode *dp = VTODC(vp);
        struct comphdr *hdr = dp->dc_hdr;
        struct page *pp;
        struct buf *bp;
        caddr_t saddr;
        off_t cblkno;
        size_t rdoff, rdsize, dsize;
        long xlen;
        int error, zerr;

        ASSERT(len == hdr->ch_blksize);
        /*
         * Get destination pages and make them addressable
         */
        pp = page_create_va(&vp->v_object, off, len, PG_WAIT, seg, addr);
        bp = pageio_setup(pp, len, vp, B_READ);
        bp_mapin(bp);

        /*
         * read compressed data from subordinate vnode
         */
        saddr = kmem_cache_alloc(dp->dc_bufcache, KM_SLEEP);
        cblkno = off / len;
        rdoff = hdr->ch_blkmap[cblkno];
        rdsize = hdr->ch_blkmap[cblkno + 1] - rdoff;
        error = vn_rdwr(UIO_READ, dp->dc_subvp, saddr, rdsize, rdoff,
            UIO_SYSSPACE, 0, 0, cr, NULL);
        if (error)
                goto cleanup;

        /*
         * Uncompress
         */
        dsize = len;
        zerr = z_uncompress(bp->b_un.b_addr, &dsize, saddr, dp->dc_zmax);
        if (zerr != Z_OK) {
                error = EIO;
                goto cleanup;
        }

        /*
         * Handle EOF
         */
        xlen = hdr->ch_fsize - off;
        if (xlen < len) {
                bzero(bp->b_un.b_addr + xlen, len - xlen);
                if (dsize != xlen)
                        error = EIO;
        } else if (dsize != len)
                error = EIO;

        /*
         * Clean up
         */
cleanup:
        kmem_cache_free(dp->dc_bufcache, saddr);
        pageio_done(bp);
        *ppp = pp;
        return (error);
}

static int
dc_getblock(struct vnode *vp, offset_t off, size_t len, struct page **ppp,
    struct seg *seg, caddr_t addr, enum seg_rw rw, struct cred *cr)
{
        struct page *pp, *plist = NULL;
        offset_t pgoff;
        int rdblk;

        /*
         * pvn_read_kluster() doesn't quite do what we want, since it
         * thinks sub block reads are ok.  Here we always decompress
         * a full block.
         */

        /*
         * Check page cache
         */
        rdblk = 0;
        for (pgoff = off; pgoff < off + len; pgoff += PAGESIZE) {
                pp = page_lookup(&vp->v_object, pgoff, SE_EXCL);
                if (pp == NULL) {
                        rdblk = 1;
                        break;
                }
                page_io_lock(pp);
                page_add(&plist, pp);
                plist = plist->p_next;
        }
        if (!rdblk) {
                *ppp = plist;
                return (0);     /* all pages in cache */
        }

        /*
         * Undo any locks so getblock_miss has an open field
         */
        if (plist != NULL)
                pvn_io_done(plist);

        return (dc_getblock_miss(vp, off, len, ppp, seg, addr, rw, cr));
}

static int
dc_realvp(vnode_t *vp, vnode_t **vpp, caller_context_t *ct)
{
        struct vnode *rvp;

        vp = VTODC(vp)->dc_subvp;
        if (fop_realvp(vp, &rvp, ct) == 0)
                vp = rvp;
        *vpp = vp;
        return (0);
}

/*ARGSUSED10*/
static int
dc_getpage(struct vnode *vp, offset_t off, size_t len, uint_t *protp,
    struct page *pl[], size_t plsz, struct seg *seg, caddr_t addr,
    enum seg_rw rw, struct cred *cr, caller_context_t *ctp)
{
        struct dcnode *dp = VTODC(vp);
        struct comphdr *hdr = dp->dc_hdr;
        struct page *pp, *plist = NULL;
        caddr_t vp_baddr;
        offset_t vp_boff, vp_bend;
        size_t bsize = hdr->ch_blksize;
        int nblks, error;

        /* does not support write */
        if (rw == S_WRITE) {
                panic("write attempt on compressed file");
                /*NOTREACHED*/
        }

        if (protp)
                *protp = PROT_ALL;
        /*
         * We don't support asynchronous operation at the moment, so
         * just pretend we did it.  If the pages are ever actually
         * needed, they'll get brought in then.
         */
        if (pl == NULL)
                return (0);

        /*
         * Calc block start and end offsets
         */
        vp_boff = rounddown(off, bsize);
        vp_bend = roundup(off + len, bsize);
        vp_baddr = (caddr_t)rounddown((uintptr_t)addr, bsize);

        nblks = (vp_bend - vp_boff) / bsize;
        while (nblks--) {
                error = dc_getblock(vp, vp_boff, bsize, &pp, seg, vp_baddr,
                    rw, cr);
                page_list_concat(&plist, &pp);
                vp_boff += bsize;
                vp_baddr += bsize;
        }
        if (!error)
                pvn_plist_init(plist, pl, plsz, off, len, rw);
        else
                pvn_read_done(plist, B_ERROR);
        return (error);
}

/*
 * This function should never be called. We need to have it to pass
 * it as an argument to other functions.
 */
/*ARGSUSED*/
static int
dc_putapage(struct vnode *vp, struct page *pp, uoff_t *offp, size_t *lenp,
    int flags, struct cred *cr)
{
        /* should never happen */
        cmn_err(CE_PANIC, "dcfs: dc_putapage: dirty page");
        /*NOTREACHED*/
        return (0);
}


/*
 * The only flags we support are B_INVAL, B_FREE and B_DONTNEED.
 * B_INVAL is set by:
 *
 *      1) the MC_SYNC command of memcntl(2) to support the MS_INVALIDATE flag.
 *      2) the MC_ADVISE command of memcntl(2) with the MADV_DONTNEED advice
 *         which translates to an MC_SYNC with the MS_INVALIDATE flag.
 *
 * The B_FREE (as well as the B_DONTNEED) flag is set when the
 * MADV_SEQUENTIAL advice has been used. fop_putpage is invoked
 * from SEGVN to release pages behind a pagefault.
 */
/*ARGSUSED5*/
static int
dc_putpage(struct vnode *vp, offset_t off, size_t len, int flags,
    struct cred *cr, caller_context_t *ctp)
{
        int error = 0;

        if (vp->v_count == 0) {
                panic("dcfs_putpage: bad v_count");
                /*NOTREACHED*/
        }

        if (vp->v_flag & VNOMAP)
                return (ENOSYS);

        if (!vn_has_cached_data(vp))    /* no pages mapped */
                return (0);

        if (len == 0)           /* from 'off' to EOF */
                error = pvn_vplist_dirty(vp, off, dc_putapage, flags, cr);
        else {
                offset_t io_off;
                se_t se = (flags & (B_INVAL | B_FREE)) ? SE_EXCL : SE_SHARED;

                for (io_off = off; io_off < off + len; io_off += PAGESIZE) {
                        page_t *pp;

                        /*
                         * We insist on getting the page only if we are
                         * about to invalidate, free or write it and
                         * the B_ASYNC flag is not set.
                         */
                        if ((flags & B_INVAL) || ((flags & B_ASYNC) == 0))
                                pp = page_lookup(&vp->v_object, io_off, se);
                        else
                                pp = page_lookup_nowait(&vp->v_object,
                                                        io_off, se);

                        if (pp == NULL)
                                continue;
                        /*
                         * Normally pvn_getdirty() should return 0, which
                         * impies that it has done the job for us.
                         * The shouldn't-happen scenario is when it returns 1.
                         * This means that the page has been modified and
                         * needs to be put back.
                         * Since we can't write to a dcfs compressed file,
                         * we fake a failed I/O and force pvn_write_done()
                         * to destroy the page.
                         */
                        if (pvn_getdirty(pp, flags) == 1) {
                                cmn_err(CE_NOTE, "dc_putpage: dirty page");
                                pvn_write_done(pp, flags |
                                    B_ERROR | B_WRITE | B_INVAL | B_FORCE);
                        }
                }
        }
        return (error);
}

static int
dc_map(struct vnode *vp, offset_t off, struct as *as, caddr_t *addrp,
    size_t len, uchar_t prot, uchar_t maxprot, uint_t flags,
    struct cred *cred, caller_context_t *ctp)
{
        struct vattr vattr;
        struct segvn_crargs vn_a;
        int error;

        if (vp->v_flag & VNOMAP)
                return (ENOSYS);

        if (off < 0 || (offset_t)(off + len) < 0)
                return (ENXIO);

        /*
         * If file is being locked, disallow mapping.
         */
        if (error = fop_getattr(VTODC(vp)->dc_subvp, &vattr, 0, cred, ctp))
                return (error);
        if (vn_has_mandatory_locks(vp, vattr.va_mode))
                return (EAGAIN);

        as_rangelock(as);

        if ((flags & MAP_FIXED) == 0) {
                map_addr(addrp, len, off, 1, flags);
                if (*addrp == NULL) {
                        as_rangeunlock(as);
                        return (ENOMEM);
                }
        } else {
                /*
                 * User specified address - blow away any previous mappings
                 */
                (void) as_unmap(as, *addrp, len);
        }

        vn_a.vp = vp;
        vn_a.offset = off;
        vn_a.type = flags & MAP_TYPE;
        vn_a.prot = prot;
        vn_a.maxprot = maxprot;
        vn_a.flags = flags & ~MAP_TYPE;
        vn_a.cred = cred;
        vn_a.amp = NULL;
        vn_a.szc = 0;
        vn_a.lgrp_mem_policy_flags = 0;

        error = as_map(as, *addrp, len, segvn_create, &vn_a);
        as_rangeunlock(as);
        return (error);
}

/*ARGSUSED*/
static int
dc_addmap(struct vnode *vp, offset_t off, struct as *as, caddr_t addr,
    size_t len, uchar_t prot, uchar_t maxprot, uint_t flags,
    struct cred *cr, caller_context_t *ctp)
{
        struct dcnode *dp;

        if (vp->v_flag & VNOMAP)
                return (ENOSYS);

        dp = VTODC(vp);
        mutex_enter(&dp->dc_lock);
        dp->dc_mapcnt += btopr(len);
        mutex_exit(&dp->dc_lock);
        return (0);
}

/*ARGSUSED*/
static int
dc_delmap(struct vnode *vp, offset_t off, struct as *as, caddr_t addr,
    size_t len, uint_t prot, uint_t maxprot, uint_t flags,
    struct cred *cr, caller_context_t *ctp)
{
        struct dcnode *dp;

        if (vp->v_flag & VNOMAP)
                return (ENOSYS);

        dp = VTODC(vp);
        mutex_enter(&dp->dc_lock);
        dp->dc_mapcnt -= btopr(len);
        ASSERT(dp->dc_mapcnt >= 0);
        mutex_exit(&dp->dc_lock);
        return (0);
}

/*
 * Constructor/destructor routines for dcnodes
 */
/*ARGSUSED1*/
static int
dcnode_constructor(void *buf, void *cdrarg, int kmflags)
{
        struct dcnode *dp = buf;
        struct vnode *vp;

        vp = dp->dc_vp = vn_alloc(kmflags);
        if (vp == NULL) {
                return (-1);
        }
        vp->v_data = dp;
        vp->v_type = VREG;
        vp->v_flag = VNOSWAP;
        vp->v_vfsp = &dc_vfs;
        vn_setops(vp, &dc_vnodeops);
        vn_exists(vp);

        mutex_init(&dp->dc_lock, NULL, MUTEX_DEFAULT, NULL);
        dp->dc_mapcnt = 0;
        dp->dc_lrunext = dp->dc_lruprev = NULL;
        dp->dc_hdr = NULL;
        dp->dc_subvp = NULL;
        return (0);
}

/*ARGSUSED*/
static void
dcnode_destructor(void *buf, void *cdrarg)
{
        struct dcnode *dp = buf;
        struct vnode *vp = DCTOV(dp);

        mutex_destroy(&dp->dc_lock);

        VERIFY(dp->dc_hdr == NULL);
        VERIFY(dp->dc_subvp == NULL);
        vn_invalid(vp);
        vn_free(vp);
}

static struct dcnode *
dcnode_alloc(void)
{
        struct dcnode *dp;

        /*
         * If the free list is above DCLRUSIZE
         * re-use one from it
         */
        mutex_enter(&dctable_lock);
        if (dclru_len < DCLRUSIZE) {
                mutex_exit(&dctable_lock);
                dp = kmem_cache_alloc(dcnode_cache, KM_SLEEP);
        } else {
                ASSERT(dclru != NULL);
                dp = dclru;
                dclru_sub(dp);
                dcdelete(dp);
                mutex_exit(&dctable_lock);
                dcnode_recycle(dp);
        }
        return (dp);
}

static void
dcnode_free(struct dcnode *dp)
{
        struct vnode *vp = DCTOV(dp);

        ASSERT(MUTEX_HELD(&dctable_lock));

        /*
         * If no cached pages, no need to put it on lru
         */
        if (!vn_has_cached_data(vp)) {
                dcdelete(dp);
                dcnode_recycle(dp);
                kmem_cache_free(dcnode_cache, dp);
                return;
        }

        /*
         * Add to lru, if it's over the limit, free from head
         */
        dclru_add(dp);
        if (dclru_len > DCLRUSIZE) {
                dp = dclru;
                dclru_sub(dp);
                dcdelete(dp);
                dcnode_recycle(dp);
                kmem_cache_free(dcnode_cache, dp);
        }
}

static void
dcnode_recycle(struct dcnode *dp)
{
        struct vnode *vp;

        vp = DCTOV(dp);

        VN_RELE(dp->dc_subvp);
        dp->dc_subvp = NULL;
        (void) pvn_vplist_dirty(vp, 0, dc_putapage, B_INVAL, NULL);
        kmem_free(dp->dc_hdr, dp->dc_hdrsize);
        dp->dc_hdr = NULL;
        dp->dc_hdrsize = dp->dc_zmax = 0;
        dp->dc_bufcache = NULL;
        dp->dc_mapcnt = 0;
        vn_reinit(vp);
        vp->v_type = VREG;
        vp->v_flag = VNOSWAP;
        vp->v_vfsp = &dc_vfs;
}

static int
dcinit(int fstype, char *name)
{
        int error;
        major_t dev;

        error = vfs_setfsops(fstype, &dc_vfsops);
        if (error) {
                cmn_err(CE_WARN, "dcinit: bad fstype");
                return (error);
        }
        VFS_INIT(&dc_vfs, &dc_vfsops, NULL);
        dc_vfs.vfs_flag = VFS_RDONLY;
        dc_vfs.vfs_fstype = fstype;
        if ((dev = getudev()) == (major_t)-1)
                dev = 0;
        dcdev = makedevice(dev, 0);
        dc_vfs.vfs_dev = dcdev;

        mutex_init(&dctable_lock, NULL, MUTEX_DEFAULT, NULL);
        mutex_init(&dccache_lock, NULL, MUTEX_DEFAULT, NULL);
        dcnode_cache = kmem_cache_create("dcnode_cache", sizeof (struct dcnode),
            0, dcnode_constructor, dcnode_destructor, NULL, NULL, NULL, 0);

        return (0);
}

/*
 * Return shadow vnode with the given vp as its subordinate
 */
struct vnode *
decompvp(struct vnode *vp, cred_t *cred, caller_context_t *ctp)
{
        struct dcnode *dp, *ndp;
        struct comphdr thdr, *hdr;
        struct kmem_cache **cpp;
        struct vattr vattr;
        size_t hdrsize, bsize;
        int error;

        /*
         * See if we have an existing shadow
         * If none, we have to manufacture one
         */
        mutex_enter(&dctable_lock);
        dp = dcfind(vp);
        mutex_exit(&dctable_lock);
        if (dp != NULL)
                return (DCTOV(dp));

        /*
         * Make sure it's a valid compressed file
         */
        hdr = &thdr;
        error = vn_rdwr(UIO_READ, vp, (caddr_t)hdr, sizeof (struct comphdr), 0,
            UIO_SYSSPACE, 0, 0, cred, NULL);
        if (error || hdr->ch_magic != CH_MAGIC_ZLIB ||
            hdr->ch_version != CH_VERSION || hdr->ch_algorithm != CH_ALG_ZLIB ||
            hdr->ch_fsize == 0 || hdr->ch_blksize < PAGESIZE ||
            hdr->ch_blksize > ptob(DCCACHESIZE) || !ISP2(hdr->ch_blksize))
                return (NULL);

        /* get underlying file size */
        if (fop_getattr(vp, &vattr, 0, cred, ctp) != 0)
                return (NULL);

        /*
         * Re-read entire header
         */
        hdrsize = hdr->ch_blkmap[0] + sizeof (uint64_t);
        hdr = kmem_alloc(hdrsize, KM_SLEEP);
        error = vn_rdwr(UIO_READ, vp, (caddr_t)hdr, hdrsize, 0, UIO_SYSSPACE,
            0, 0, cred, NULL);
        if (error) {
                kmem_free(hdr, hdrsize);
                return (NULL);
        }

        /*
         * add extra blkmap entry to make dc_getblock()'s
         * life easier
         */
        bsize = hdr->ch_blksize;
        hdr->ch_blkmap[((hdr->ch_fsize-1) / bsize) + 1] = vattr.va_size;

        ndp = dcnode_alloc();
        ndp->dc_subvp = vp;
        VN_HOLD(vp);
        ndp->dc_hdr = hdr;
        ndp->dc_hdrsize = hdrsize;

        /*
         * Allocate kmem cache if none there already
         */
        ndp->dc_zmax = ZMAXBUF(bsize);
        cpp = &dcbuf_cache[btop(bsize)];
        mutex_enter(&dccache_lock);
        if (*cpp == NULL)
                *cpp = kmem_cache_create("dcbuf_cache", ndp->dc_zmax, 0, NULL,
                    NULL, NULL, NULL, NULL, 0);
        mutex_exit(&dccache_lock);
        ndp->dc_bufcache = *cpp;

        /*
         * Recheck table in case someone else created shadow
         * while we were blocked above.
         */
        mutex_enter(&dctable_lock);
        dp = dcfind(vp);
        if (dp != NULL) {
                mutex_exit(&dctable_lock);
                dcnode_recycle(ndp);
                kmem_cache_free(dcnode_cache, ndp);
                return (DCTOV(dp));
        }
        dcinsert(ndp);
        mutex_exit(&dctable_lock);

        return (DCTOV(ndp));
}


/*
 * dcnode lookup table
 * These routines maintain a table of dcnodes hashed by their
 * subordinate vnode so that they can be found if they already
 * exist in the vnode cache
 */

/*
 * Put a dcnode in the table.
 */
static void
dcinsert(struct dcnode *newdp)
{
        int idx = DCHASH(newdp->dc_subvp);

        ASSERT(MUTEX_HELD(&dctable_lock));
        newdp->dc_hash = dctable[idx];
        dctable[idx] = newdp;
}

/*
 * Remove a dcnode from the hash table.
 */
void
dcdelete(struct dcnode *deldp)
{
        int idx = DCHASH(deldp->dc_subvp);
        struct dcnode *dp, *prevdp;

        ASSERT(MUTEX_HELD(&dctable_lock));
        dp = dctable[idx];
        if (dp == deldp)
                dctable[idx] = dp->dc_hash;
        else {
                for (prevdp = dp, dp = dp->dc_hash; dp != NULL;
                    prevdp = dp, dp = dp->dc_hash) {
                        if (dp == deldp) {
                                prevdp->dc_hash = dp->dc_hash;
                                break;
                        }
                }
        }
        ASSERT(dp != NULL);
}

/*
 * Find a shadow vnode in the dctable hash list.
 */
static struct dcnode *
dcfind(struct vnode *vp)
{
        struct dcnode *dp;

        ASSERT(MUTEX_HELD(&dctable_lock));
        for (dp = dctable[DCHASH(vp)]; dp != NULL; dp = dp->dc_hash)
                if (dp->dc_subvp == vp) {
                        VN_HOLD(DCTOV(dp));
                        if (dp->dc_lrunext)
                                dclru_sub(dp);
                        return (dp);
                }
        return (NULL);
}

#ifdef  DEBUG
static int
dclru_count(void)
{
        struct dcnode *dp;
        int i = 0;

        if (dclru == NULL)
                return (0);
        for (dp = dclru; dp->dc_lrunext != dclru; dp = dp->dc_lrunext)
                i++;
        return (i + 1);
}
#endif

static void
dclru_add(struct dcnode *dp)
{
        /*
         * Add to dclru as double-link chain
         */
        ASSERT(MUTEX_HELD(&dctable_lock));
        if (dclru == NULL) {
                dclru = dp;
                dp->dc_lruprev = dp->dc_lrunext = dp;
        } else {
                struct dcnode *last = dclru->dc_lruprev;

                dclru->dc_lruprev = dp;
                last->dc_lrunext = dp;
                dp->dc_lruprev = last;
                dp->dc_lrunext = dclru;
        }
        dclru_len++;
        ASSERT(dclru_len == dclru_count());
}

static void
dclru_sub(struct dcnode *dp)
{
        ASSERT(MUTEX_HELD(&dctable_lock));
        dp->dc_lrunext->dc_lruprev = dp->dc_lruprev;
        dp->dc_lruprev->dc_lrunext = dp->dc_lrunext;
        if (dp == dclru)
                dclru = dp->dc_lrunext == dp ? NULL : dp->dc_lrunext;
        dp->dc_lrunext = dp->dc_lruprev = NULL;
        dclru_len--;
        ASSERT(dclru_len == dclru_count());
}