/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
 * Copyright (c) 2006 Tobias Reifenberger
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS 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 AUTHORS 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 <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/malloc.h>

#include <geom/geom.h>
#include <geom/geom_dbg.h>
#include <geom/label/g_label.h>
#include <geom/label/g_label_msdosfs.h>

#define LABEL_NO_NAME           "NO NAME    "

static void
g_label_msdosfs_taste(struct g_consumer *cp, char *label, size_t size)
{
        struct g_provider *pp;
        FAT_BSBPB *pfat_bsbpb;
        FAT32_BSBPB *pfat32_bsbpb;
        FAT_DES *pfat_entry;
        uint8_t *sector0, *sector;
        size_t copysize;

        g_topology_assert_not();
        pp = cp->provider;
        sector0 = NULL;
        sector = NULL;
        bzero(label, size);

        /* Check if the sector size of the medium is a valid FAT sector size. */
        switch(pp->sectorsize) {
        case 512:
        case 1024:
        case 2048:
        case 4096:
                break;
        default:
                G_LABEL_DEBUG(1, "MSDOSFS: %s: sector size %d not compatible.",
                    pp->name, pp->sectorsize);
                return;
        }

        /* Load 1st sector with boot sector and boot parameter block. */
        sector0 = (uint8_t *)g_read_data(cp, 0, pp->sectorsize, NULL);
        if (sector0 == NULL)
                return;

        /* Check for the FAT boot sector signature. */
        if (sector0[510] != 0x55 || sector0[511] != 0xaa) {
                G_LABEL_DEBUG(1, "MSDOSFS: %s: no FAT signature found.",
                    pp->name);
                goto error;
        }

        /*
         * Test if this is really a FAT volume and determine the FAT type.
         */

        pfat_bsbpb = (FAT_BSBPB *)sector0;
        pfat32_bsbpb = (FAT32_BSBPB *)sector0;

        if (UINT16BYTES(pfat_bsbpb->BPB_FATSz16) != 0) {
                /*
                 * If the BPB_FATSz16 field is not zero and the string "FAT" is
                 * at the right place, this should be a FAT12 or FAT16 volume.
                 */
                if (strncmp(pfat_bsbpb->BS_FilSysType, "FAT", 3) != 0) {
                        G_LABEL_DEBUG(1,
                            "MSDOSFS: %s: FAT12/16 volume not valid.",
                            pp->name);
                        goto error;
                }
                G_LABEL_DEBUG(1, "MSDOSFS: %s: FAT12/FAT16 volume detected.",
                    pp->name);

                /* A volume with no name should have "NO NAME    " as label. */
                if (strncmp(pfat_bsbpb->BS_VolLab, LABEL_NO_NAME,
                    sizeof(pfat_bsbpb->BS_VolLab)) == 0) {
                        G_LABEL_DEBUG(1,
                            "MSDOSFS: %s: FAT12/16 volume has no name.",
                            pp->name);
                        goto error;
                }
                copysize = MIN(size - 1, sizeof(pfat_bsbpb->BS_VolLab));
                memcpy(label, pfat_bsbpb->BS_VolLab, copysize);
                label[copysize] = '\0';
        } else if (UINT32BYTES(pfat32_bsbpb->BPB_FATSz32) != 0) {
                uint32_t fat_FirstDataSector, fat_BytesPerSector, offset;

                /*
                 * If the BPB_FATSz32 field is not zero and the string "FAT" is
                 * at the right place, this should be a FAT32 volume.
                 */
                if (strncmp(pfat32_bsbpb->BS_FilSysType, "FAT", 3) != 0) {
                        G_LABEL_DEBUG(1, "MSDOSFS: %s: FAT32 volume not valid.",
                            pp->name);
                        goto error;
                }
                G_LABEL_DEBUG(1, "MSDOSFS: %s: FAT32 volume detected.",
                    pp->name);

                /*
                 * If the volume label is not "NO NAME    " we're done.
                 */
                if (strncmp(pfat32_bsbpb->BS_VolLab, LABEL_NO_NAME,
                    sizeof(pfat32_bsbpb->BS_VolLab)) != 0) {
                        copysize = MIN(size - 1,
                            sizeof(pfat32_bsbpb->BS_VolLab));
                        memcpy(label, pfat32_bsbpb->BS_VolLab, copysize);
                        label[copysize] = '\0';
                        goto endofchecks;
                }

                /*
                 * If the volume label "NO NAME    " is in the boot sector, the
                 * label of FAT32 volumes may be stored as a special entry in
                 * the root directory.
                 */
                fat_FirstDataSector =
                    UINT16BYTES(pfat32_bsbpb->BPB_RsvdSecCnt) +
                    (pfat32_bsbpb->BPB_NumFATs *
                     UINT32BYTES(pfat32_bsbpb->BPB_FATSz32));
                fat_BytesPerSector = UINT16BYTES(pfat32_bsbpb->BPB_BytsPerSec);

                G_LABEL_DEBUG(2,
                    "MSDOSFS: FAT_FirstDataSector=0x%x, FAT_BytesPerSector=%d",
                    fat_FirstDataSector, fat_BytesPerSector);
                if (fat_BytesPerSector == 0 ||
                    fat_BytesPerSector % pp->sectorsize != 0) {
                        G_LABEL_DEBUG(1, "MSDOSFS: %s: corrupted BPB",
                            pp->name);
                        goto error;
                }

                for (offset = fat_BytesPerSector * fat_FirstDataSector;;
                    offset += fat_BytesPerSector) {
                        sector = (uint8_t *)g_read_data(cp, offset,
                            fat_BytesPerSector, NULL);
                        if (sector == NULL)
                                goto error;

                        pfat_entry = (FAT_DES *)sector;
                        do {
                                /* No more entries available. */
                                if (pfat_entry->DIR_Name[0] == 0) {
                                        G_LABEL_DEBUG(1, "MSDOSFS: %s: "
                                            "FAT32 volume has no name.",
                                            pp->name);
                                        goto error;
                                }

                                /* Skip empty or long name entries. */
                                if (pfat_entry->DIR_Name[0] == 0xe5 ||
                                    (pfat_entry->DIR_Attr &
                                     FAT_DES_ATTR_LONG_NAME) ==
                                    FAT_DES_ATTR_LONG_NAME) {
                                        continue;
                                }

                                /*
                                 * The name of the entry is the volume label if
                                 * ATTR_VOLUME_ID is set.
                                 */
                                if (pfat_entry->DIR_Attr &
                                    FAT_DES_ATTR_VOLUME_ID) {
                                        copysize = MIN(size - 1,
                                            sizeof(pfat_entry->DIR_Name));
                                        memcpy(label, pfat_entry->DIR_Name,
                                            copysize);
                                        label[copysize] = '\0';
                                        goto endofchecks;
                                }
                        } while((uint8_t *)(++pfat_entry) <
                            (uint8_t *)(sector + fat_BytesPerSector));
                        g_free(sector);
                }
        } else {
                G_LABEL_DEBUG(1, "MSDOSFS: %s: no FAT volume detected.",
                    pp->name);
                goto error;
        }

endofchecks:
        g_label_rtrim(label, size);

error:
        g_free(sector0);
        g_free(sector);
}

struct g_label_desc g_label_msdosfs = {
        .ld_taste = g_label_msdosfs_taste,
        .ld_dirprefix = "msdosfs/",
        .ld_enabled = 1
};

G_LABEL_INIT(msdosfs, g_label_msdosfs, "Create device nodes for MSDOSFS volumes");