/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2013 Juniper Networks, Inc.
 * Copyright (c) 2022-2023 Klara, Inc.
 *
 * 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 "opt_tarfs.h"
#include "opt_zstdio.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/counter.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/sysctl.h>
#include <sys/uio.h>
#include <sys/vnode.h>

#if defined(ZSTDIO)
#define TARFS_ZIO 1
#else
#undef TARFS_ZIO
#endif

#ifdef ZSTDIO
#define ZSTD_STATIC_LINKING_ONLY
#include <contrib/zstd/lib/zstd.h>
#endif

#include <fs/tarfs/tarfs.h>
#include <fs/tarfs/tarfs_dbg.h>

#ifdef TARFS_DEBUG
SYSCTL_NODE(_vfs_tarfs, OID_AUTO, zio, CTLFLAG_RD, 0,
    "Tar filesystem decompression layer");
COUNTER_U64_DEFINE_EARLY(tarfs_zio_inflated);
SYSCTL_COUNTER_U64(_vfs_tarfs_zio, OID_AUTO, inflated, CTLFLAG_RD,
    &tarfs_zio_inflated, "Amount of compressed data inflated.");
COUNTER_U64_DEFINE_EARLY(tarfs_zio_consumed);
SYSCTL_COUNTER_U64(_vfs_tarfs_zio, OID_AUTO, consumed, CTLFLAG_RD,
    &tarfs_zio_consumed, "Amount of compressed data consumed.");
COUNTER_U64_DEFINE_EARLY(tarfs_zio_bounced);
SYSCTL_COUNTER_U64(_vfs_tarfs_zio, OID_AUTO, bounced, CTLFLAG_RD,
    &tarfs_zio_bounced, "Amount of decompressed data bounced.");

static int
tarfs_sysctl_handle_zio_reset(SYSCTL_HANDLER_ARGS)
{
        unsigned int tmp;
        int error;

        tmp = 0;
        if ((error = SYSCTL_OUT(req, &tmp, sizeof(tmp))) != 0)
                return (error);
        if (req->newptr != NULL) {
                if ((error = SYSCTL_IN(req, &tmp, sizeof(tmp))) != 0)
                        return (error);
                counter_u64_zero(tarfs_zio_inflated);
                counter_u64_zero(tarfs_zio_consumed);
                counter_u64_zero(tarfs_zio_bounced);
        }
        return (0);
}

SYSCTL_PROC(_vfs_tarfs_zio, OID_AUTO, reset,
    CTLTYPE_INT | CTLFLAG_MPSAFE | CTLFLAG_RW,
    NULL, 0, tarfs_sysctl_handle_zio_reset, "IU",
    "Reset compression counters.");
#endif

MALLOC_DEFINE(M_TARFSZSTATE, "tarfs zstate", "tarfs decompression state");
MALLOC_DEFINE(M_TARFSZBUF, "tarfs zbuf", "tarfs decompression buffers");

#define XZ_MAGIC                (uint8_t[]){ 0xfd, 0x37, 0x7a, 0x58, 0x5a }
#define ZLIB_MAGIC              (uint8_t[]){ 0x1f, 0x8b, 0x08 }
#define ZSTD_MAGIC              (uint8_t[]){ 0x28, 0xb5, 0x2f, 0xfd }

#ifdef ZSTDIO
struct tarfs_zstd {
        ZSTD_DStream *zds;
};
#endif

/* XXX review use of curthread / uio_td / td_cred */

/*
 * Reads from the tar file according to the provided uio.  If the archive
 * is compressed and raw is false, reads the decompressed stream;
 * otherwise, reads directly from the original file.  Returns 0 on success
 * and a positive errno value on failure.
 */
int
tarfs_io_read(struct tarfs_mount *tmp, bool raw, struct uio *uiop)
{
        void *rl = NULL;
        off_t off = uiop->uio_offset;
        size_t len = uiop->uio_resid;
        int error;

        if (raw || tmp->znode == NULL) {
                rl = vn_rangelock_rlock(tmp->vp, off, off + len);
                error = vn_lock(tmp->vp, LK_SHARED);
                if (error == 0) {
                        error = VOP_READ(tmp->vp, uiop, IO_NODELOCKED,
                            uiop->uio_td->td_ucred);
                        VOP_UNLOCK(tmp->vp);
                }
                vn_rangelock_unlock(tmp->vp, rl);
        } else {
                error = vn_lock(tmp->znode, LK_EXCLUSIVE);
                if (error == 0) {
                        error = VOP_READ(tmp->znode, uiop,
                            IO_DIRECT | IO_NODELOCKED,
                            uiop->uio_td->td_ucred);
                        VOP_UNLOCK(tmp->znode);
                }
        }
        TARFS_DPF(IO, "%s(%zu, %zu) = %d (resid %zd)\n", __func__,
            (size_t)off, len, error, uiop->uio_resid);
        return (error);
}

/*
 * Reads from the tar file into the provided buffer.  If the archive is
 * compressed and raw is false, reads the decompressed stream; otherwise,
 * reads directly from the original file.  Returns the number of bytes
 * read on success, 0 on EOF, and a negative errno value on failure.
 */
ssize_t
tarfs_io_read_buf(struct tarfs_mount *tmp, bool raw,
    void *buf, off_t off, size_t len)
{
        struct uio auio;
        struct iovec aiov;
        ssize_t res;
        int error;

        if (len == 0) {
                TARFS_DPF(IO, "%s(%zu, %zu) null\n", __func__,
                    (size_t)off, len);
                return (0);
        }
        aiov.iov_base = buf;
        aiov.iov_len = len;
        auio.uio_iov = &aiov;
        auio.uio_iovcnt = 1;
        auio.uio_offset = off;
        auio.uio_segflg = UIO_SYSSPACE;
        auio.uio_rw = UIO_READ;
        auio.uio_resid = len;
        auio.uio_td = curthread;
        error = tarfs_io_read(tmp, raw, &auio);
        if (error != 0) {
                TARFS_DPF(IO, "%s(%zu, %zu) error %d\n", __func__,
                    (size_t)off, len, error);
                return (-error);
        }
        res = len - auio.uio_resid;
        if (res == 0 && len != 0) {
                TARFS_DPF(IO, "%s(%zu, %zu) eof\n", __func__,
                    (size_t)off, len);
        } else {
                TARFS_DPF(IO, "%s(%zu, %zu) read %zd | %*D\n", __func__,
                    (size_t)off, len, res,
                    (int)(res > 8 ? 8 : res), (uint8_t *)buf, " ");
        }
        return (res);
}

#ifdef ZSTDIO
static void *
tarfs_zstate_alloc(void *opaque, size_t size)
{

        (void)opaque;
        return (malloc(size, M_TARFSZSTATE, M_WAITOK));
}
#endif

#ifdef ZSTDIO
static void
tarfs_zstate_free(void *opaque, void *address)
{

        (void)opaque;
        free(address, M_TARFSZSTATE);
}
#endif

#ifdef ZSTDIO
static ZSTD_customMem tarfs_zstd_mem = {
        tarfs_zstate_alloc,
        tarfs_zstate_free,
        NULL,
};
#endif

#ifdef TARFS_ZIO
/*
 * Updates the decompression frame index, recording the current input and
 * output offsets in a new index entry, and growing the index if
 * necessary.
 */
static void
tarfs_zio_update_index(struct tarfs_zio *zio, off_t i, off_t o)
{

        if (++zio->curidx >= zio->nidx) {
                if (++zio->nidx > zio->szidx) {
                        zio->szidx *= 2;
                        zio->idx = realloc(zio->idx,
                            zio->szidx * sizeof(*zio->idx),
                            M_TARFSZSTATE, M_ZERO | M_WAITOK);
                        TARFS_DPF(ALLOC, "%s: resized zio index\n", __func__);
                }
                zio->idx[zio->curidx].i = i;
                zio->idx[zio->curidx].o = o;
                TARFS_DPF(ZIDX, "%s: index %u = i %zu o %zu\n", __func__,
                    zio->curidx, (size_t)zio->idx[zio->curidx].i,
                    (size_t)zio->idx[zio->curidx].o);
        }
        MPASS(zio->idx[zio->curidx].i == i);
        MPASS(zio->idx[zio->curidx].o == o);
}
#endif

/*
 * VOP_ACCESS for zio node.
 */
static int
tarfs_zaccess(struct vop_access_args *ap)
{
        struct vnode *vp = ap->a_vp;
        struct tarfs_zio *zio = vp->v_data;
        struct tarfs_mount *tmp = zio->tmp;
        accmode_t accmode = ap->a_accmode;
        int error = EPERM;

        if (accmode == VREAD) {
                error = vn_lock(tmp->vp, LK_SHARED);
                if (error == 0) {
                        error = VOP_ACCESS(tmp->vp, accmode, ap->a_cred, ap->a_td);
                        VOP_UNLOCK(tmp->vp);
                }
        }
        TARFS_DPF(ZIO, "%s(%d) = %d\n", __func__, accmode, error);
        return (error);
}

/*
 * VOP_GETATTR for zio node.
 */
static int
tarfs_zgetattr(struct vop_getattr_args *ap)
{
        struct vattr va;
        struct vnode *vp = ap->a_vp;
        struct tarfs_zio *zio = vp->v_data;
        struct tarfs_mount *tmp = zio->tmp;
        struct vattr *vap = ap->a_vap;
        int error = 0;

        VATTR_NULL(vap);
        error = vn_lock(tmp->vp, LK_SHARED);
        if (error == 0) {
                error = VOP_GETATTR(tmp->vp, &va, ap->a_cred);
                VOP_UNLOCK(tmp->vp);
                if (error == 0) {
                        vap->va_type = VREG;
                        vap->va_mode = va.va_mode;
                        vap->va_nlink = 1;
                        vap->va_gid = va.va_gid;
                        vap->va_uid = va.va_uid;
                        vap->va_fsid = vp->v_mount->mnt_stat.f_fsid.val[0];
                        vap->va_fileid = TARFS_ZIOINO;
                        vap->va_size = zio->idx[zio->nidx - 1].o;
                        vap->va_blocksize = vp->v_mount->mnt_stat.f_iosize;
                        vap->va_atime = va.va_atime;
                        vap->va_ctime = va.va_ctime;
                        vap->va_mtime = va.va_mtime;
                        vap->va_birthtime = tmp->root->birthtime;
                        vap->va_bytes = va.va_bytes;
                }
        }
        TARFS_DPF(ZIO, "%s() = %d\n", __func__, error);
        return (error);
}

#ifdef ZSTDIO
/*
 * VOP_READ for zio node, zstd edition.
 */
static int
tarfs_zread_zstd(struct tarfs_zio *zio, struct uio *uiop)
{
        void *ibuf = NULL, *obuf = NULL, *rl = NULL;
        struct uio auio;
        struct iovec aiov;
        struct tarfs_mount *tmp = zio->tmp;
        struct tarfs_zstd *zstd = zio->zstd;
        struct thread *td = curthread;
        ZSTD_inBuffer zib;
        ZSTD_outBuffer zob;
        off_t zsize;
        off_t ipos, opos;
        size_t ilen, olen;
        size_t zerror;
        off_t off = uiop->uio_offset;
        size_t len = uiop->uio_resid;
        size_t resid = uiop->uio_resid;
        size_t bsize;
        int error;
        bool reset = false;

        /* do we have to rewind? */
        if (off < zio->opos) {
                while (zio->curidx > 0 && off < zio->idx[zio->curidx].o)
                        zio->curidx--;
                reset = true;
        }
        /* advance to the nearest index entry */
        if (off > zio->opos) {
                // XXX maybe do a binary search instead
                while (zio->curidx < zio->nidx - 1 &&
                    off >= zio->idx[zio->curidx + 1].o) {
                        zio->curidx++;
                        reset = true;
                }
        }
        /* reset the decompression stream if needed */
        if (reset) {
                zio->ipos = zio->idx[zio->curidx].i;
                zio->opos = zio->idx[zio->curidx].o;
                ZSTD_DCtx_reset(zstd->zds, ZSTD_reset_session_only);
                TARFS_DPF(ZIDX, "%s: skipping to index %u = i %zu o %zu\n", __func__,
                    zio->curidx, (size_t)zio->ipos, (size_t)zio->opos);
        } else {
                TARFS_DPF(ZIDX, "%s: continuing at i %zu o %zu\n", __func__,
                    (size_t)zio->ipos, (size_t)zio->opos);
        }

        /*
         * Set up a temporary buffer for compressed data.  Use the size
         * recommended by the zstd library; this is usually 128 kB, but
         * just in case, make sure it's a multiple of the page size and no
         * larger than MAXBSIZE.
         */
        bsize = roundup(ZSTD_CStreamOutSize(), PAGE_SIZE);
        if (bsize > MAXBSIZE)
                bsize = MAXBSIZE;
        ibuf = malloc(bsize, M_TEMP, M_WAITOK);
        zib.src = NULL;
        zib.size = 0;
        zib.pos = 0;

        /*
         * Set up the decompression buffer.  If the target is not in
         * kernel space, we will have to set up a bounce buffer.
         *
         * TODO: to avoid using a bounce buffer, map destination pages
         * using vm_fault_quick_hold_pages().
         */
        MPASS(zio->opos <= off);
        MPASS(uiop->uio_iovcnt == 1);
        MPASS(uiop->uio_iov->iov_len >= len);
        if (uiop->uio_segflg == UIO_SYSSPACE) {
                zob.dst = uiop->uio_iov->iov_base;
        } else {
                TARFS_DPF(BOUNCE, "%s: allocating %zu-byte bounce buffer\n",
                    __func__, len);
                zob.dst = obuf = malloc(len, M_TEMP, M_WAITOK);
        }
        zob.size = len;
        zob.pos = 0;

        /* lock tarball */
        rl = vn_rangelock_rlock(tmp->vp, zio->ipos, OFF_MAX);
        error = vn_lock(tmp->vp, LK_SHARED);
        if (error != 0) {
                goto fail_unlocked;
        }
        /* check size */
        error = vn_getsize_locked(tmp->vp, &zsize, td->td_ucred);
        if (error != 0) {
                goto fail;
        }
        if (zio->ipos >= zsize) {
                /* beyond EOF */
                goto fail;
        }

        while (resid > 0) {
                if (zib.pos == zib.size) {
                        /* request data from the underlying file */
                        aiov.iov_base = ibuf;
                        aiov.iov_len = bsize;
                        auio.uio_iov = &aiov;
                        auio.uio_iovcnt = 1;
                        auio.uio_offset = zio->ipos;
                        auio.uio_segflg = UIO_SYSSPACE;
                        auio.uio_rw = UIO_READ;
                        auio.uio_resid = aiov.iov_len;
                        auio.uio_td = td;
                        error = VOP_READ(tmp->vp, &auio, IO_NODELOCKED,
                            td->td_ucred);
                        if (error != 0)
                                goto fail;
                        TARFS_DPF(ZIO, "%s: req %zu+%zu got %zu+%zu\n", __func__,
                            (size_t)zio->ipos, bsize,
                            (size_t)zio->ipos, bsize - auio.uio_resid);
                        zib.src = ibuf;
                        zib.size = bsize - auio.uio_resid;
                        zib.pos = 0;
                }
                MPASS(zib.pos <= zib.size);
                if (zib.pos == zib.size) {
                        TARFS_DPF(ZIO, "%s: end of file after i %zu o %zu\n", __func__,
                            (size_t)zio->ipos, (size_t)zio->opos);
                        goto fail;
                }
                if (zio->opos < off) {
                        /* to be discarded */
                        zob.size = MIN(off - zio->opos, len);
                        zob.pos = 0;
                } else {
                        zob.size = len;
                        zob.pos = zio->opos - off;
                }
                ipos = zib.pos;
                opos = zob.pos;
                /* decompress as much as possible */
                zerror = ZSTD_decompressStream(zstd->zds, &zob, &zib);
                zio->ipos += ilen = zib.pos - ipos;
                zio->opos += olen = zob.pos - opos;
                if (zio->opos > off)
                        resid -= olen;
                if (ZSTD_isError(zerror)) {
                        TARFS_DPF(ZIO, "%s: inflate failed after i %zu o %zu: %s\n", __func__,
                            (size_t)zio->ipos, (size_t)zio->opos, ZSTD_getErrorName(zerror));
                        error = EIO;
                        goto fail;
                }
                if (zerror == 0 && olen == 0) {
                        TARFS_DPF(ZIO, "%s: end of stream after i %zu o %zu\n", __func__,
                            (size_t)zio->ipos, (size_t)zio->opos);
                        break;
                }
                if (zerror == 0) {
                        TARFS_DPF(ZIO, "%s: end of frame after i %zu o %zu\n", __func__,
                            (size_t)zio->ipos, (size_t)zio->opos);
                        tarfs_zio_update_index(zio, zio->ipos, zio->opos);
                }
                TARFS_DPF(ZIO, "%s: inflated %zu\n", __func__, olen);
#ifdef TARFS_DEBUG
                counter_u64_add(tarfs_zio_inflated, olen);
#endif
        }
fail:
        VOP_UNLOCK(tmp->vp);
fail_unlocked:
        if (error == 0) {
                if (uiop->uio_segflg == UIO_SYSSPACE) {
                        uiop->uio_resid = resid;
                } else if (len > resid) {
                        TARFS_DPF(BOUNCE, "%s: bounced %zu bytes\n", __func__,
                            len - resid);
                        error = uiomove(obuf, len - resid, uiop);
#ifdef TARFS_DEBUG
                        counter_u64_add(tarfs_zio_bounced, len - resid);
#endif
                }
        }
        if (obuf != NULL) {
                TARFS_DPF(BOUNCE, "%s: freeing bounce buffer\n", __func__);
                free(obuf, M_TEMP);
        }
        if (rl != NULL)
                vn_rangelock_unlock(tmp->vp, rl);
        if (ibuf != NULL)
                free(ibuf, M_TEMP);
        TARFS_DPF(ZIO, "%s(%zu, %zu) = %d (resid %zd)\n", __func__,
            (size_t)off, len, error, uiop->uio_resid);
#ifdef TARFS_DEBUG
        counter_u64_add(tarfs_zio_consumed, len - uiop->uio_resid);
#endif
        if (error != 0) {
                zio->curidx = 0;
                zio->ipos = zio->idx[0].i;
                zio->opos = zio->idx[0].o;
                ZSTD_DCtx_reset(zstd->zds, ZSTD_reset_session_only);
        }
        return (error);
}
#endif

/*
 * VOP_READ for zio node.
 */
static int
tarfs_zread(struct vop_read_args *ap)
{
#if defined(TARFS_DEBUG) || defined(ZSTDIO)
        struct vnode *vp = ap->a_vp;
        struct tarfs_zio *zio = vp->v_data;
        struct uio *uiop = ap->a_uio;
#endif
#ifdef TARFS_DEBUG
        off_t off = uiop->uio_offset;
        size_t len = uiop->uio_resid;
#endif
        int error;

        TARFS_DPF(ZIO, "%s(%zu, %zu)\n", __func__,
            (size_t)off, len);
#ifdef ZSTDIO
        if (zio->zstd != NULL) {
                error = tarfs_zread_zstd(zio, uiop);
        } else
#endif
                error = EFTYPE;
        TARFS_DPF(ZIO, "%s(%zu, %zu) = %d (resid %zd)\n", __func__,
            (size_t)off, len, error, uiop->uio_resid);
        return (error);
}

/*
 * VOP_RECLAIM for zio node.
 */
static int
tarfs_zreclaim(struct vop_reclaim_args *ap)
{
        struct vnode *vp = ap->a_vp;

        TARFS_DPF(ZIO, "%s(%p)\n", __func__, vp);
        vp->v_data = NULL;
        return (0);
}

/*
 * VOP_STRATEGY for zio node.
 */
static int
tarfs_zstrategy(struct vop_strategy_args *ap)
{
        struct uio auio;
        struct iovec iov;
        struct vnode *vp = ap->a_vp;
        struct buf *bp = ap->a_bp;
        off_t off;
        size_t len;
        int error;

        iov.iov_base = bp->b_data;
        iov.iov_len = bp->b_bcount;
        off = bp->b_iooffset;
        len = bp->b_bcount;
        bp->b_resid = len;
        auio.uio_iov = &iov;
        auio.uio_iovcnt = 1;
        auio.uio_offset = off;
        auio.uio_resid = len;
        auio.uio_segflg = UIO_SYSSPACE;
        auio.uio_rw = UIO_READ;
        auio.uio_td = curthread;
        error = VOP_READ(vp, &auio, IO_DIRECT | IO_NODELOCKED, bp->b_rcred);
        bp->b_flags |= B_DONE;
        if (error != 0) {
                bp->b_ioflags |= BIO_ERROR;
                bp->b_error = error;
        }
        return (0);
}

static struct vop_vector tarfs_znodeops = {
        .vop_default =          &default_vnodeops,

        .vop_access =           tarfs_zaccess,
        .vop_getattr =          tarfs_zgetattr,
        .vop_read =             tarfs_zread,
        .vop_reclaim =          tarfs_zreclaim,
        .vop_strategy =         tarfs_zstrategy,
};
VFS_VOP_VECTOR_REGISTER(tarfs_znodeops);

#ifdef TARFS_ZIO
/*
 * Initializes the decompression layer.
 */
static struct tarfs_zio *
tarfs_zio_init(struct tarfs_mount *tmp, off_t i, off_t o)
{
        struct tarfs_zio *zio;
        struct vnode *zvp;

        zio = malloc(sizeof(*zio), M_TARFSZSTATE, M_ZERO | M_WAITOK);
        TARFS_DPF(ALLOC, "%s: allocated zio\n", __func__);
        zio->tmp = tmp;
        zio->szidx = 128;
        zio->idx = malloc(zio->szidx * sizeof(*zio->idx), M_TARFSZSTATE,
            M_ZERO | M_WAITOK);
        zio->curidx = 0;
        zio->nidx = 1;
        zio->idx[zio->curidx].i = zio->ipos = i;
        zio->idx[zio->curidx].o = zio->opos = o;
        tmp->zio = zio;
        TARFS_DPF(ALLOC, "%s: allocated zio index\n", __func__);
        (void)getnewvnode("tarfsz", tmp->vfs, &tarfs_znodeops, &zvp);
        zvp->v_data = zio;
        zvp->v_type = VREG;
        zvp->v_mount = tmp->vfs;
        vn_set_state(zvp, VSTATE_CONSTRUCTED);
        tmp->znode = zvp;
        TARFS_DPF(ZIO, "%s: created zio node\n", __func__);
        return (zio);
}
#endif

/*
 * Initializes the I/O layer, including decompression if the signature of
 * a supported compression format is detected.  Returns 0 on success and a
 * positive errno value on failure.
 */
int
tarfs_io_init(struct tarfs_mount *tmp)
{
        uint8_t *block;
#ifdef TARFS_ZIO
        struct tarfs_zio *zio = NULL;
#endif
        ssize_t res;
        int error = 0;

        block = malloc(tmp->iosize, M_TEMP, M_ZERO | M_WAITOK);
        res = tarfs_io_read_buf(tmp, true, block, 0, tmp->iosize);
        if (res < 0) {
                return (-res);
        }
        if (memcmp(block, XZ_MAGIC, sizeof(XZ_MAGIC)) == 0) {
                printf("xz compression not supported\n");
                error = EOPNOTSUPP;
                goto bad;
        } else if (memcmp(block, ZLIB_MAGIC, sizeof(ZLIB_MAGIC)) == 0) {
                printf("zlib compression not supported\n");
                error = EOPNOTSUPP;
                goto bad;
        } else if (memcmp(block, ZSTD_MAGIC, sizeof(ZSTD_MAGIC)) == 0) {
#ifdef ZSTDIO
                zio = tarfs_zio_init(tmp, 0, 0);
                zio->zstd = malloc(sizeof(*zio->zstd), M_TARFSZSTATE, M_WAITOK);
                zio->zstd->zds = ZSTD_createDStream_advanced(tarfs_zstd_mem);
                (void)ZSTD_initDStream(zio->zstd->zds);
#else
                printf("zstd compression not supported\n");
                error = EOPNOTSUPP;
                goto bad;
#endif
        }
bad:
        free(block, M_TEMP);
        return (error);
}

#ifdef TARFS_ZIO
/*
 * Tears down the decompression layer.
 */
static int
tarfs_zio_fini(struct tarfs_mount *tmp)
{
        struct tarfs_zio *zio = tmp->zio;
        int error = 0;

        if (tmp->znode != NULL) {
                error = vn_lock(tmp->znode, LK_EXCLUSIVE);
                if (error != 0) {
                        TARFS_DPF(ALLOC, "%s: failed to lock znode", __func__);
                        return (error);
                }
                tmp->znode->v_mount = NULL;
                vgone(tmp->znode);
                vput(tmp->znode);
                tmp->znode = NULL;
        }
#ifdef ZSTDIO
        if (zio->zstd != NULL) {
                TARFS_DPF(ALLOC, "%s: freeing zstd state\n", __func__);
                ZSTD_freeDStream(zio->zstd->zds);
                free(zio->zstd, M_TARFSZSTATE);
        }
#endif
        if (zio->idx != NULL) {
                TARFS_DPF(ALLOC, "%s: freeing index\n", __func__);
                free(zio->idx, M_TARFSZSTATE);
        }
        TARFS_DPF(ALLOC, "%s: freeing zio\n", __func__);
        free(zio, M_TARFSZSTATE);
        tmp->zio = NULL;
        return (error);
}
#endif

/*
 * Tears down the I/O layer, including the decompression layer if
 * applicable.
 */
int
tarfs_io_fini(struct tarfs_mount *tmp)
{
        int error = 0;

#ifdef TARFS_ZIO
        if (tmp->zio != NULL) {
                error = tarfs_zio_fini(tmp);
        }
#endif
        return (error);
}