FreeBSD/Linux Kernel Cross Reference
sys/geom/geom_bsd.c

     /*-
      * Copyright (c) 2002 Poul-Henning Kamp
      * Copyright (c) 2002 Networks Associates Technology, Inc.
      * All rights reserved.
      *
      * This software was developed for the FreeBSD Project by Poul-Henning Kamp
      * and NAI Labs, the Security Research Division of Network Associates, Inc.
      * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
      * DARPA CHATS research program.
     *
     * 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. The names of the authors may not be used to endorse or promote
     *    products derived from this software without specific prior written
     *    permission.
     *
     * 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.
     *
     * $FreeBSD: releng/5.0/sys/geom/geom_bsd.c 109195 2003-01-13 21:09:20Z jhb $
     *
     * This is the method for dealing with BSD disklabels.  It has been
     * extensively (by my standards at least) commented, in the vain hope that
     * it will server as the source in future copy&paste operations.
     */
    
    #include <sys/param.h>
    #ifndef _KERNEL
    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    #include <signal.h>
    #include <err.h>
    #else
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/conf.h>
    #include <sys/bio.h>
    #include <sys/malloc.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #endif
    #include <sys/stdint.h>
    #include <sys/errno.h>
    #include <sys/disklabel.h>
    #include <geom/geom.h>
    #include <geom/geom_slice.h>
    
    #define BSD_CLASS_NAME "BSD"
    
    #define ALPHA_LABEL_OFFSET      64
    
    /*
     * Our private data about one instance.  All the rest is handled by the
     * slice code and stored in its softc, so this is just the stuff
     * specific to BSD disklabels.
     */
    struct g_bsd_softc {
            off_t   labeloffset;
            off_t   mbroffset;
            off_t   rawoffset;
            struct disklabel ondisk;
            struct disklabel inram;
    };
    
    /*
     * The next 4 functions isolate us from how the compiler lays out and pads
     * "struct disklabel".  We treat what we read from disk as a bytestream and
     * explicitly convert it into a struct disklabel.  This makes us compiler-
     * endianness- and wordsize- agnostic.
     * For now we only have little-endian formats to deal with.
     */
    
    static void
    g_bsd_ledec_partition(u_char *ptr, struct partition *d)
    {
            d->p_size = g_dec_le4(ptr + 0);
            d->p_offset = g_dec_le4(ptr + 4);
            d->p_fsize = g_dec_le4(ptr + 8);
            d->p_fstype = ptr[12];
            d->p_frag = ptr[13];
            d->p_cpg = g_dec_le2(ptr + 14);
    }
    
   static void
   g_bsd_ledec_disklabel(u_char *ptr, struct disklabel *d)
   {
           int i;
   
           d->d_magic = g_dec_le4(ptr + 0);
           d->d_type = g_dec_le2(ptr + 4);
           d->d_subtype = g_dec_le2(ptr + 6);
           bcopy(ptr + 8, d->d_typename, 16);
           bcopy(ptr + 24, d->d_packname, 16);
           d->d_secsize = g_dec_le4(ptr + 40);
           d->d_nsectors = g_dec_le4(ptr + 44);
           d->d_ntracks = g_dec_le4(ptr + 48);
           d->d_ncylinders = g_dec_le4(ptr + 52);
           d->d_secpercyl = g_dec_le4(ptr + 56);
           d->d_secperunit = g_dec_le4(ptr + 60);
           d->d_sparespertrack = g_dec_le2(ptr + 64);
           d->d_sparespercyl = g_dec_le2(ptr + 66);
           d->d_acylinders = g_dec_le4(ptr + 68);
           d->d_rpm = g_dec_le2(ptr + 72);
           d->d_interleave = g_dec_le2(ptr + 74);
           d->d_trackskew = g_dec_le2(ptr + 76);
           d->d_cylskew = g_dec_le2(ptr + 78);
           d->d_headswitch = g_dec_le4(ptr + 80);
           d->d_trkseek = g_dec_le4(ptr + 84);
           d->d_flags = g_dec_le4(ptr + 88);
           d->d_drivedata[0] = g_dec_le4(ptr + 92);
           d->d_drivedata[1] = g_dec_le4(ptr + 96);
           d->d_drivedata[2] = g_dec_le4(ptr + 100);
           d->d_drivedata[3] = g_dec_le4(ptr + 104);
           d->d_drivedata[4] = g_dec_le4(ptr + 108);
           d->d_spare[0] = g_dec_le4(ptr + 112);
           d->d_spare[1] = g_dec_le4(ptr + 116);
           d->d_spare[2] = g_dec_le4(ptr + 120);
           d->d_spare[3] = g_dec_le4(ptr + 124);
           d->d_spare[4] = g_dec_le4(ptr + 128);
           d->d_magic2 = g_dec_le4(ptr + 132);
           d->d_checksum = g_dec_le2(ptr + 136);
           d->d_npartitions = g_dec_le2(ptr + 138);
           d->d_bbsize = g_dec_le4(ptr + 140);
           d->d_sbsize = g_dec_le4(ptr + 144);
           for (i = 0; i < MAXPARTITIONS; i++)
                   g_bsd_ledec_partition(ptr + 148 + 16 * i, &d->d_partitions[i]);
   }
   
   static void
   g_bsd_leenc_partition(u_char *ptr, struct partition *d)
   {
           g_enc_le4(ptr + 0, d->p_size);
           g_enc_le4(ptr + 4, d->p_offset);
           g_enc_le4(ptr + 8, d->p_fsize);
           ptr[12] = d->p_fstype;
           ptr[13] = d->p_frag;
           g_enc_le2(ptr + 14, d->p_cpg);
   }
   
   static void
   g_bsd_leenc_disklabel(u_char *ptr, struct disklabel *d)
   {
           int i;
   
           g_enc_le4(ptr + 0, d->d_magic);
           g_enc_le2(ptr + 4, d->d_type);
           g_enc_le2(ptr + 6, d->d_subtype);
           bcopy(d->d_typename, ptr + 8, 16);
           bcopy(d->d_packname, ptr + 24, 16);
           g_enc_le4(ptr + 40, d->d_secsize);
           g_enc_le4(ptr + 44, d->d_nsectors);
           g_enc_le4(ptr + 48, d->d_ntracks);
           g_enc_le4(ptr + 52, d->d_ncylinders);
           g_enc_le4(ptr + 56, d->d_secpercyl);
           g_enc_le4(ptr + 60, d->d_secperunit);
           g_enc_le2(ptr + 64, d->d_sparespertrack);
           g_enc_le2(ptr + 66, d->d_sparespercyl);
           g_enc_le4(ptr + 68, d->d_acylinders);
           g_enc_le2(ptr + 72, d->d_rpm);
           g_enc_le2(ptr + 74, d->d_interleave);
           g_enc_le2(ptr + 76, d->d_trackskew);
           g_enc_le2(ptr + 78, d->d_cylskew);
           g_enc_le4(ptr + 80, d->d_headswitch);
           g_enc_le4(ptr + 84, d->d_trkseek);
           g_enc_le4(ptr + 88, d->d_flags);
           g_enc_le4(ptr + 92, d->d_drivedata[0]);
           g_enc_le4(ptr + 96, d->d_drivedata[1]);
           g_enc_le4(ptr + 100, d->d_drivedata[2]);
           g_enc_le4(ptr + 104, d->d_drivedata[3]);
           g_enc_le4(ptr + 108, d->d_drivedata[4]);
           g_enc_le4(ptr + 112, d->d_spare[0]);
           g_enc_le4(ptr + 116, d->d_spare[1]);
           g_enc_le4(ptr + 120, d->d_spare[2]);
           g_enc_le4(ptr + 124, d->d_spare[3]);
           g_enc_le4(ptr + 128, d->d_spare[4]);
           g_enc_le4(ptr + 132, d->d_magic2);
           g_enc_le2(ptr + 136, d->d_checksum);
           g_enc_le2(ptr + 138, d->d_npartitions);
           g_enc_le4(ptr + 140, d->d_bbsize);
           g_enc_le4(ptr + 144, d->d_sbsize);
           for (i = 0; i < MAXPARTITIONS; i++)
                   g_bsd_leenc_partition(ptr + 148 + 16 * i, &d->d_partitions[i]);
   }
   
   static int
   g_bsd_ondisk_size(void)
   {
           return (148 + 16 * MAXPARTITIONS);
   }
   
   /*
    * For reasons which were valid and just in their days, FreeBSD/i386 uses
    * absolute disk-addresses in disklabels.  The way it works is that the
    * p_offset field of all partitions have the first sector number of the
    * disk slice added to them.  This was hidden kernel-magic, userland did
    * not see these offsets.  These two functions subtract and add them
    * while converting from the "ondisk" to the "inram" labels and vice
    * versa.
    */
   static void
   ondisk2inram(struct g_bsd_softc *sc)
   {
           struct partition *ppp;
           struct disklabel *dl;
           int i;
   
           sc->inram = sc->ondisk;
           dl = &sc->inram;
   
           /* Basic sanity-check needed to avoid mistakes. */
           if (dl->d_magic != DISKMAGIC || dl->d_magic2 != DISKMAGIC)
                   return;
           if (dl->d_npartitions > MAXPARTITIONS)
                   return;
   
           sc->rawoffset = dl->d_partitions[RAW_PART].p_offset;
           for (i = 0; i < dl->d_npartitions; i++) {
                   ppp = &dl->d_partitions[i];
                   if (ppp->p_size != 0 && ppp->p_offset < sc->rawoffset)
                           sc->rawoffset = 0;
           }
           if (sc->rawoffset > 0) {
                   for (i = 0; i < dl->d_npartitions; i++) {
                           ppp = &dl->d_partitions[i];
                           if (ppp->p_offset != 0)
                                   ppp->p_offset -= sc->rawoffset;
                   }
           }
           dl->d_checksum = 0;
           dl->d_checksum = dkcksum(&sc->inram);
   }
   
   static void
   inram2ondisk(struct g_bsd_softc *sc)
   {
           struct partition *ppp;
           int i;
   
           sc->ondisk = sc->inram;
           if (sc->mbroffset != 0)
                   sc->rawoffset = sc->mbroffset / sc->inram.d_secsize; 
           if (sc->rawoffset != 0) {
                   for (i = 0; i < sc->inram.d_npartitions; i++) {
                           ppp = &sc->ondisk.d_partitions[i];
                           if (ppp->p_size > 0) 
                                   ppp->p_offset += sc->rawoffset;
                           else
                                   ppp->p_offset = 0;
                   }
           }
           sc->ondisk.d_checksum = 0;
           sc->ondisk.d_checksum = dkcksum(&sc->ondisk);
   }
   
   /*
    * Check that this looks like a valid disklabel, but be prepared
    * to get any kind of junk.  The checksum must be checked only
    * after this function returns success to prevent a bogus d_npartitions
    * value from tripping us up.
    */
   static int
   g_bsd_checklabel(struct disklabel *dl)
   {
           struct partition *ppp;
           int i;
   
           if (dl->d_magic != DISKMAGIC || dl->d_magic2 != DISKMAGIC)
                   return (EINVAL);
           /*
            * If the label specifies more partitions than we can handle
            * we have to reject it:  If people updated the label they would
            * trash it, and that would break the checksum.
            */
           if (dl->d_npartitions > MAXPARTITIONS)
                   return (EINVAL);
   
           for (i = 0; i < dl->d_npartitions; i++) {
                   ppp = &dl->d_partitions[i];
                   /* Cannot extend past unit. */
                   if (ppp->p_size != 0 &&
                        ppp->p_offset + ppp->p_size > dl->d_secperunit) {
                           return (EINVAL);
                   }
           }
           return (0);
   }
   
   /*
    * Modify our slicer to match proposed disklabel, if possible.
    * First carry out all the simple checks, then lock topology
    * and check that no open providers are affected negatively
    * then carry out all the changes.
    *
    * NB: Returns with topology held only if successful return.
    */
   static int
   g_bsd_modify(struct g_geom *gp, struct disklabel *dl)
   {
           int i, error;
           struct partition *ppp;
           struct g_slicer *gsp;
           struct g_consumer *cp;
           u_int secsize, u;
           off_t mediasize;
   
           /* Basic check that this is indeed a disklabel. */
           error = g_bsd_checklabel(dl);
           if (error)
                   return (error);
   
           /* Make sure the checksum is OK. */
           if (dkcksum(dl) != 0)
                   return (EINVAL);
   
           /* Get dimensions of our device. */
           cp = LIST_FIRST(&gp->consumer);
           secsize = cp->provider->sectorsize;
           mediasize = cp->provider->mediasize;
   
   #ifdef nolonger
           /*
            * The raw-partition must start at zero.  We do not check that the
            * size == mediasize because this is overly restrictive.  We have
            * already tested in g_bsd_checklabel() that it is not longer.
            * XXX: RAW_PART is archaic anyway, and we should drop it.
            */
           if (dl->d_partitions[RAW_PART].p_offset != 0)
                   return (EINVAL);
   #endif
   
   #ifdef notyet
           /*
            * Indications are that the d_secperunit is not correctly
            * initialized in many cases, and since we don't need it
            * for anything, we dont strictly need this test.
            * Preemptive action to avoid confusing people in disklabel(8)
            * may be in order.
            */
           /* The label cannot claim a larger size than the media. */
           if ((off_t)dl->d_secperunit * dl->d_secsize > mediasize)
                   return (EINVAL);
   #endif
   
   
           /* ... or a smaller sector size. */
           if (dl->d_secsize < secsize)
                   return (EINVAL);
   
           /* ... or a non-multiple sector size. */
           if (dl->d_secsize % secsize != 0)
                   return (EINVAL);
   
           g_topology_lock();
   
           /* Don't munge open partitions. */
           gsp = gp->softc;
           for (i = 0; i < dl->d_npartitions; i++) {
                   ppp = &dl->d_partitions[i];
   
                   error = g_slice_config(gp, i, G_SLICE_CONFIG_CHECK,
                       (off_t)ppp->p_offset * dl->d_secsize,
                       (off_t)ppp->p_size * dl->d_secsize,
                        dl->d_secsize,
                       "%s%c", gp->name, 'a' + i);
                   if (error) {
                           g_topology_unlock();
                           return (error);
                   }
           }
   
           /* Look good, go for it... */
           for (u = 0; u < gsp->nslice; u++) {
                   ppp = &dl->d_partitions[u];
                   g_slice_config(gp, u, G_SLICE_CONFIG_SET,
                       (off_t)ppp->p_offset * dl->d_secsize,
                       (off_t)ppp->p_size * dl->d_secsize,
                        dl->d_secsize,
                       "%s%c", gp->name, 'a' + u);
           }
           return (0);
   }
   
   /*
    * Calculate a disklabel checksum for a little-endian byte-stream.
    * We need access to the decoded disklabel because the checksum only
    * covers the partition data for the first d_npartitions.
    */
   static int
   g_bsd_lesum(struct disklabel *dl, u_char *p)
   {
           u_char *pe;
           uint16_t sum;
   
           pe = p + 148 + 16 * dl->d_npartitions;
           sum = 0;
           while (p < pe) {
                   sum ^= g_dec_le2(p);
                   p += 2;
           }
           return (sum);
   }
   
   /*
    * This is an internal helper function, called multiple times from the taste
    * function to try to locate a disklabel on the disk.  More civilized formats
    * will not need this, as there is only one possible place on disk to look
    * for the magic spot.
    */
   
   static int
   g_bsd_try(struct g_geom *gp, struct g_slicer *gsp, struct g_consumer *cp, int secsize, struct g_bsd_softc *ms, off_t offset)
   {
           int error;
           u_char *buf;
           struct disklabel *dl;
           off_t secoff;
   
           /*
            * We need to read entire aligned sectors, and we assume that the
            * disklabel does not span sectors, so one sector is enough.
            */
           error = 0;
           secoff = offset % secsize;
           buf = g_read_data(cp, offset - secoff, secsize, &error);
           if (buf == NULL || error != 0)
                   return (ENOENT);
   
           /* Decode into our native format. */
           dl = &ms->ondisk;
           g_bsd_ledec_disklabel(buf + secoff, dl);
   
           ondisk2inram(ms);
   
           dl = &ms->inram;
           /* Does it look like a label at all? */
           if (g_bsd_checklabel(dl))
                   error = ENOENT;
           /* ... and does the raw data have a good checksum? */
           if (error == 0 && g_bsd_lesum(dl, buf + secoff) != 0)
                   error = ENOENT;
   
           /* Remember to free the buffer g_read_data() gave us. */
           g_free(buf);
   
           /* If we had a label, record it properly. */
           if (error == 0) {
                   gsp->frontstuff = 16 * secsize; /* XXX */
                   ms->labeloffset = offset;
                   g_topology_lock();
                   g_slice_conf_hot(gp, 0, offset, g_bsd_ondisk_size());
                   g_topology_unlock();
           }
           return (error);
   }
   
   /*
    * Implement certain ioctls to modify disklabels with.  This function
    * is called by the event handler thread with topology locked as result
    * of the g_call_me() in g_bsd_start().  It is not necessary to keep
    * topology locked all the time but make sure to return with topology
    * locked as well.
    */
   
   static void
   g_bsd_ioctl(void *arg)
   {
           struct bio *bp;
           struct g_geom *gp;
           struct g_slicer *gsp;
           struct g_bsd_softc *ms;
           struct disklabel *dl;
           struct g_ioctl *gio;
           struct g_consumer *cp;
           u_char *buf;
           off_t secoff;
           u_int secsize;
           int error, i;
           uint64_t sum;
   
           /* We don't need topology for now. */
           g_topology_unlock();
   
           /* Get hold of the interesting bits from the bio. */
           bp = arg;
           gp = bp->bio_to->geom;
           gsp = gp->softc;
           ms = gsp->softc;
           gio = (struct g_ioctl *)bp->bio_data;
   
           /* The disklabel to set is the ioctl argument. */
           dl = gio->data;
   
           /* Validate and modify our slice instance to match. */
           error = g_bsd_modify(gp, dl);   /* Picks up topology lock on success. */
           if (error) {
                   g_topology_lock();
                   g_io_deliver(bp, error);
                   return;
           }
           /* Update our copy of the disklabel. */
           ms->inram = *dl;
           inram2ondisk(ms);
   
           if (gio->cmd == DIOCSDINFO) {
                   g_io_deliver(bp, 0);
                   return;
           }
           KASSERT(gio->cmd == DIOCWDINFO, ("Unknown ioctl in g_bsd_ioctl"));
           cp = LIST_FIRST(&gp->consumer);
           /* Get sector size, we need it to read data. */
           secsize = cp->provider->sectorsize;
           secoff = ms->labeloffset % secsize;
           buf = g_read_data(cp, ms->labeloffset - secoff, secsize, &error);
           if (buf == NULL || error != 0) {
                   g_io_deliver(bp, error);
                   return;
           }
           dl = &ms->ondisk;
           g_bsd_leenc_disklabel(buf + secoff, dl);
           if (ms->labeloffset == ALPHA_LABEL_OFFSET) {
                   sum = 0;
                   for (i = 0; i < 63; i++)
                           sum += g_dec_le8(buf + i * 8);
                   g_enc_le8(buf + 504, sum);
           }
           error = g_write_data(cp, ms->labeloffset - secoff, buf, secsize);
           g_free(buf);
           g_io_deliver(bp, error);
   }
   
   /*
    * If the user tries to overwrite our disklabel through an open partition
    * or via a magicwrite config call, we end up here and try to prevent
    * footshooting as best we can.
    */
   static void
   g_bsd_hotwrite(void *arg)
   {
           struct bio *bp;
           struct g_geom *gp;
           struct g_slicer *gsp;
           struct g_slice *gsl;
           struct g_bsd_softc *ms;
           struct g_bsd_softc fake;
           u_char *p;
           int error;
           
           bp = arg;
           gp = bp->bio_to->geom;
           gsp = gp->softc;
           ms = gsp->softc;
           gsl = &gsp->slices[bp->bio_to->index];
           p = (u_char*)bp->bio_data + ms->labeloffset 
               - (bp->bio_offset + gsl->offset);
           g_bsd_ledec_disklabel(p, &fake.ondisk);
           
           ondisk2inram(&fake);
           if (g_bsd_checklabel(&fake.inram)) {
                   g_io_deliver(bp, EPERM);
                   return;
           }
           if (g_bsd_lesum(&fake.ondisk, p) != 0) {
                   g_io_deliver(bp, EPERM);
                   return;
           }
           g_topology_unlock();
           error = g_bsd_modify(gp, &fake.inram);  /* May pick up topology. */
           if (error) {
                   g_io_deliver(bp, EPERM);
                   g_topology_lock();
                   return;
           }
           /* Update our copy of the disklabel. */
           ms->inram = fake.inram;
           inram2ondisk(ms);
           g_bsd_leenc_disklabel(p, &ms->ondisk);
           g_slice_finish_hot(bp);
   }
   
   /*-
    * This start routine is only called for non-trivial requests, all the
    * trivial ones are handled autonomously by the slice code.
    * For requests we handle here, we must call the g_io_deliver() on the
    * bio, and return non-zero to indicate to the slice code that we did so.
    * This code executes in the "DOWN" I/O path, this means:
    *    * No sleeping.
    *    * Don't grab the topology lock.
    *    * Don't call biowait, g_getattr(), g_setattr() or g_read_data()
    */
   
   static int
   g_bsd_start(struct bio *bp)
   {
           struct g_geom *gp;
           struct g_bsd_softc *ms;
           struct g_slicer *gsp;
           struct g_ioctl *gio;
           int error;
   
           gp = bp->bio_to->geom;
           gsp = gp->softc;
           ms = gsp->softc;
           switch(bp->bio_cmd) {
           case BIO_READ:
                   /* We allow reading of our hot spots */
                   return (0);
           case BIO_DELETE:
                   /* We do not allow deleting our hot spots */
                   return (EPERM);
           case BIO_WRITE:
                   g_call_me(g_bsd_hotwrite, bp);
                   return (EJUSTRETURN);
           case BIO_GETATTR:
           case BIO_SETATTR:
                   break;
           default:
                   KASSERT(0 == 1, ("Unknown bio_cmd in g_bsd_start (%d)",
                       bp->bio_cmd));
           }
   
           /* We only handle ioctl(2) requests of the right format. */
           if (strcmp(bp->bio_attribute, "GEOM::ioctl"))
                   return (0);
           else if (bp->bio_length != sizeof(*gio))
                   return (0);
   
           /* Get hold of the ioctl parameters. */
           gio = (struct g_ioctl *)bp->bio_data;
   
           switch (gio->cmd) {
           case DIOCGDINFO:
                   /* Return a copy of the disklabel to userland. */
                   bcopy(&ms->inram, gio->data, sizeof(ms->inram));
                   g_io_deliver(bp, 0);
                   return (1);
           case DIOCSDINFO:
           case DIOCWDINFO:
                   /*
                    * These we cannot do without the topology lock and some
                    * some I/O requests.  Ask the event-handler to schedule
                    * us in a less restricted environment.
                    */
                   error = g_call_me(g_bsd_ioctl, bp);
                   if (error)
                           g_io_deliver(bp, error);
                   /*
                    * We must return non-zero to indicate that we will deal
                    * with this bio, even though we have not done so yet.
                    */
                   return (1);
           default:
                   return (0);
           }
   }
   
   /*
    * Dump configuration information in XML format.
    * Notice that the function is called once for the geom and once for each
    * consumer and provider.  We let g_slice_dumpconf() do most of the work.
    */
   static void
   g_bsd_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp, struct g_consumer *cp, struct g_provider *pp)
   {
           struct g_bsd_softc *ms;
           struct g_slicer *gsp;
   
           gsp = gp->softc;
           ms = gsp->softc;
           g_slice_dumpconf(sb, indent, gp, cp, pp);
           if (indent != NULL && pp == NULL && cp == NULL) {
                   sbuf_printf(sb, "%s<labeloffset>%jd</labeloffset>\n",
                       indent, (intmax_t)ms->labeloffset);
                   sbuf_printf(sb, "%s<rawoffset>%jd</rawoffset>\n",
                       indent, (intmax_t)ms->rawoffset);
                   sbuf_printf(sb, "%s<mbroffset>%jd</mbroffset>\n",
                       indent, (intmax_t)ms->mbroffset);
           } else if (pp != NULL) {
                   if (indent == NULL)
                           sbuf_printf(sb, " ty %d",
                               ms->inram.d_partitions[pp->index].p_fstype);
                   else
                           sbuf_printf(sb, "%s<type>%d</type>\n", indent,
                               ms->inram.d_partitions[pp->index].p_fstype);
           }
   }
   
   /*
    * The taste function is called from the event-handler, with the topology
    * lock already held and a provider to examine.  The flags are unused.
    *
    * If flags == G_TF_NORMAL, the idea is to take a bite of the provider and
    * if we find valid, consistent magic on it, build a geom on it.
    * any magic bits which indicate that we should automatically put a BSD
    * geom on it.
    *
    * There may be cases where the operator would like to put a BSD-geom on
    * providers which do not meet all of the requirements.  This can be done
    * by instead passing the G_TF_INSIST flag, which will override these
    * checks.
    *
    * The final flags value is G_TF_TRANSPARENT, which instructs the method
    * to put a geom on top of the provider and configure it to be as transparent
    * as possible.  This is not really relevant to the BSD method and therefore
    * not implemented here.
    */
   
   static struct g_geom *
   g_bsd_taste(struct g_class *mp, struct g_provider *pp, int flags)
   {
           struct g_geom *gp;
           struct g_consumer *cp;
           int error, i;
           struct g_bsd_softc *ms;
           struct disklabel *dl;
           u_int secsize;
           struct g_slicer *gsp;
   
           g_trace(G_T_TOPOLOGY, "bsd_taste(%s,%s)", mp->name, pp->name);
           g_topology_assert();
   
           /* We don't implement transparent inserts. */
           if (flags == G_TF_TRANSPARENT)
                   return (NULL);
   
           /*
            * The BSD-method will not automatically configure itself recursively
            * Note that it is legal to examine the class-name of our provider,
            * nothing else should ever be examined inside the provider.
            */
           if (flags == G_TF_NORMAL &&
               !strcmp(pp->geom->class->name, BSD_CLASS_NAME))
                   return (NULL);
   
           /*
            * BSD labels are a subclass of the general "slicing" topology so
            * a lot of the work can be done by the common "slice" code.
            * Create a geom with space for MAXPARTITIONS providers, one consumer
            * and a softc structure for us.  Specify the provider to attach
            * the consumer to and our "start" routine for special requests.
            * The provider is opened with mode (1,0,0) so we can do reads
            * from it.
            */
           gp = g_slice_new(mp, MAXPARTITIONS, pp, &cp, &ms,
                sizeof(*ms), g_bsd_start);
           if (gp == NULL)
                   return (NULL);
   
           /*
            * Now that we have attached to and opened our provider, we do
            * not need the topology lock until we change the topology again
            * next time.
            */
           g_topology_unlock();
   
           /*
            * Fill in the optional details, in our case we have a dumpconf
            * routine which the "slice" code should call at the right time
            */
           gp->dumpconf = g_bsd_dumpconf;
   
           /* Get the geom_slicer softc from the geom. */
           gsp = gp->softc;
   
           /*
            * The do...while loop here allows us to have multiple escapes
            * using a simple "break".  This improves code clarity without
            * ending up in deep nesting and without using goto or come from.
            */
           do {
                   /*
                    * If the provider is an MBR we will only auto attach
                    * to type 165 slices in the G_TF_NORMAL case.  We will
                    * attach to any other type (BSD was handles above)
                    */
                   error = g_getattr("MBR::type", cp, &i);
                   if (!error) {
                           if (i != 165 && flags == G_TF_NORMAL)
                                   break;
                           error = g_getattr("MBR::offset", cp, &ms->mbroffset);
                           if (error)
                                   break;
                   }
   
                   /* Same thing if we are inside a PC98 */
                   error = g_getattr("PC98::type", cp, &i);
                   if (!error) {
                           if (i != 0xc494 && flags == G_TF_NORMAL)
                                   break;
                           error = g_getattr("PC98::offset", cp, &ms->mbroffset);
                           if (error)
                                   break;
                   }
   
                   /* Get sector size, we need it to read data. */
                   secsize = cp->provider->sectorsize;
                   if (secsize < 512)
                           break;
   
                   /* First look for a label at the start of the second sector. */
                   error = g_bsd_try(gp, gsp, cp, secsize, ms, secsize);
   
                   /* Next, look for alpha labels */
                   if (error)
                           error = g_bsd_try(gp, gsp, cp, secsize, ms,
                               ALPHA_LABEL_OFFSET);
   
                   /* If we didn't find a label, punt. */
                   if (error)
                           break;
   
                   /*
                    * Process the found disklabel, and modify our "slice"
                    * instance to match it, if possible.
                    */
                   dl = &ms->inram;
                   error = g_bsd_modify(gp, dl);   /* Picks up topology lock. */
                   if (!error)
                           g_topology_unlock();
                   break;
           } while (0);
   
           /* Success of failure, we can close our provider now. */
           g_topology_lock();
           error = g_access_rel(cp, -1, 0, 0);
   
           /* If we have configured any providers, return the new geom. */
           if (gsp->nprovider > 0)
                   return (gp);
           /*
            * ...else push the "self-destruct" button, by spoiling our own
            * consumer.  This triggers a call to g_std_spoiled which will
            * dismantle what was setup.
            */
           g_std_spoiled(cp);
           return (NULL);
   }
   
   /* Finally, register with GEOM infrastructure. */
   static struct g_class g_bsd_class = {
           BSD_CLASS_NAME,
           g_bsd_taste,
           NULL,
           G_CLASS_INITIALIZER
   };
   
   DECLARE_GEOM_CLASS(g_bsd_class, g_bsd);

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