drivers/scsi/scsicam.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.
0004  *
0005  * Copyright 1993, 1994 Drew Eckhardt
0006  *      Visionary Computing
0007  *      (Unix and Linux consulting and custom programming)
0008  *      drew@Colorado.EDU
0009  *      +1 (303) 786-7975
0010  *
0011  * For more information, please consult the SCSI-CAM draft.
0012  */
0013
0014 #include <linux/module.h>
0015 #include <linux/slab.h>
0016 #include <linux/fs.h>
0017 #include <linux/kernel.h>
0018 #include <linux/blkdev.h>
0019 #include <linux/pagemap.h>
0020 #include <linux/msdos_partition.h>
0021 #include <asm/unaligned.h>
0022
0023 #include <scsi/scsicam.h>
0024
0025 /**
0026  * scsi_bios_ptable - Read PC partition table out of first sector of device.
0027  * @dev: from this device
0028  *
0029  * Description: Reads the first sector from the device and returns %0x42 bytes
0030  *              starting at offset %0x1be.
0031  * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error.
0032  */
0033 unsigned char *scsi_bios_ptable(struct block_device *dev)
0034 {
0035     struct address_space *mapping = bdev_whole(dev)->bd_inode->i_mapping;
0036     unsigned char *res = NULL;
0037     struct folio *folio;
0038
0039     folio = read_mapping_folio(mapping, 0, NULL);
0040     if (IS_ERR(folio))
0041         return NULL;
0042
0043     res = kmemdup(folio_address(folio) + 0x1be, 66, GFP_KERNEL);
0044     folio_put(folio);
0045     return res;
0046 }
0047 EXPORT_SYMBOL(scsi_bios_ptable);
0048
0049 /**
0050  * scsi_partsize - Parse cylinders/heads/sectors from PC partition table
0051  * @bdev: block device to parse
0052  * @capacity: size of the disk in sectors
0053  * @geom: output in form of [hds, cylinders, sectors]
0054  *
0055  * Determine the BIOS mapping/geometry used to create the partition
0056  * table, storing the results in @geom.
0057  *
0058  * Returns: %false on failure, %true on success.
0059  */
0060 bool scsi_partsize(struct block_device *bdev, sector_t capacity, int geom[3])
0061 {
0062     int cyl, ext_cyl, end_head, end_cyl, end_sector;
0063     unsigned int logical_end, physical_end, ext_physical_end;
0064     struct msdos_partition *p, *largest = NULL;
0065     void *buf;
0066     int ret = false;
0067
0068     buf = scsi_bios_ptable(bdev);
0069     if (!buf)
0070         return false;
0071
0072     if (*(unsigned short *) (buf + 64) == 0xAA55) {
0073         int largest_cyl = -1, i;
0074
0075         for (i = 0, p = buf; i < 4; i++, p++) {
0076             if (!p->sys_ind)
0077                 continue;
0078 #ifdef DEBUG
0079             printk("scsicam_bios_param : partition %d has system \n",
0080                    i);
0081 #endif
0082             cyl = p->cyl + ((p->sector & 0xc0) << 2);
0083             if (cyl > largest_cyl) {
0084                 largest_cyl = cyl;
0085                 largest = p;
0086             }
0087         }
0088     }
0089     if (largest) {
0090         end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
0091         end_head = largest->end_head;
0092         end_sector = largest->end_sector & 0x3f;
0093
0094         if (end_head + 1 == 0 || end_sector == 0)
0095             goto out_free_buf;
0096
0097 #ifdef DEBUG
0098         printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
0099                end_head, end_cyl, end_sector);
0100 #endif
0101
0102         physical_end = end_cyl * (end_head + 1) * end_sector +
0103             end_head * end_sector + end_sector;
0104
0105         /* This is the actual _sector_ number at the end */
0106         logical_end = get_unaligned_le32(&largest->start_sect)
0107             + get_unaligned_le32(&largest->nr_sects);
0108
0109         /* This is for >1023 cylinders */
0110         ext_cyl = (logical_end - (end_head * end_sector + end_sector))
0111             / (end_head + 1) / end_sector;
0112         ext_physical_end = ext_cyl * (end_head + 1) * end_sector +
0113             end_head * end_sector + end_sector;
0114
0115 #ifdef DEBUG
0116         printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"
0117           ,logical_end, physical_end, ext_physical_end, ext_cyl);
0118 #endif
0119
0120         if (logical_end == physical_end ||
0121             (end_cyl == 1023 && ext_physical_end == logical_end)) {
0122             geom[0] = end_head + 1;
0123             geom[1] = end_sector;
0124             geom[2] = (unsigned long)capacity /
0125                 ((end_head + 1) * end_sector);
0126             ret = true;
0127             goto out_free_buf;
0128         }
0129 #ifdef DEBUG
0130         printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
0131                logical_end, physical_end);
0132 #endif
0133     }
0134
0135 out_free_buf:
0136     kfree(buf);
0137     return ret;
0138 }
0139 EXPORT_SYMBOL(scsi_partsize);
0140
0141 /*
0142  * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
0143  *      unsigned int *hds, unsigned int *secs);
0144  *
0145  * Purpose : to determine a near-optimal int 0x13 mapping for a
0146  *      SCSI disk in terms of lost space of size capacity, storing
0147  *      the results in *cyls, *hds, and *secs.
0148  *
0149  * Returns : -1 on failure, 0 on success.
0150  *
0151  * Extracted from
0152  *
0153  * WORKING                                                    X3T9.2
0154  * DRAFT                                                        792D
0155  * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
0156  *
0157  *                                                        Revision 6
0158  *                                                         10-MAR-94
0159  * Information technology -
0160  * SCSI-2 Common access method
0161  * transport and SCSI interface module
0162  *
0163  * ANNEX A :
0164  *
0165  * setsize() converts a read capacity value to int 13h
0166  * head-cylinder-sector requirements. It minimizes the value for
0167  * number of heads and maximizes the number of cylinders. This
0168  * will support rather large disks before the number of heads
0169  * will not fit in 4 bits (or 6 bits). This algorithm also
0170  * minimizes the number of sectors that will be unused at the end
0171  * of the disk while allowing for very large disks to be
0172  * accommodated. This algorithm does not use physical geometry.
0173  */
0174
0175 static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
0176            unsigned int *secs)
0177 {
0178     unsigned int rv = 0;
0179     unsigned long heads, sectors, cylinders, temp;
0180
0181     cylinders = 1024L;  /* Set number of cylinders to max */
0182     sectors = 62L;      /* Maximize sectors per track */
0183
0184     temp = cylinders * sectors; /* Compute divisor for heads */
0185     heads = capacity / temp;    /* Compute value for number of heads */
0186     if (capacity % temp) {  /* If no remainder, done! */
0187         heads++;    /* Else, increment number of heads */
0188         temp = cylinders * heads;   /* Compute divisor for sectors */
0189         sectors = capacity / temp;  /* Compute value for sectors per
0190                            track */
0191         if (capacity % temp) {  /* If no remainder, done! */
0192             sectors++;  /* Else, increment number of sectors */
0193             temp = heads * sectors;     /* Compute divisor for cylinders */
0194             cylinders = capacity / temp;    /* Compute number of cylinders */
0195         }
0196     }
0197     if (cylinders == 0)
0198         rv = (unsigned) -1; /* Give error if 0 cylinders */
0199
0200     *cyls = (unsigned int) cylinders;   /* Stuff return values */
0201     *secs = (unsigned int) sectors;
0202     *hds = (unsigned int) heads;
0203     return (rv);
0204 }
0205
0206 /**
0207  * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.
0208  * @bdev: which device
0209  * @capacity: size of the disk in sectors
0210  * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
0211  *
0212  * Description : determine the BIOS mapping/geometry used for a drive in a
0213  *      SCSI-CAM system, storing the results in ip as required
0214  *      by the HDIO_GETGEO ioctl().
0215  *
0216  * Returns : -1 on failure, 0 on success.
0217  */
0218 int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)
0219 {
0220     u64 capacity64 = capacity;  /* Suppress gcc warning */
0221     int ret = 0;
0222
0223     /* try to infer mapping from partition table */
0224     if (scsi_partsize(bdev, capacity, ip))
0225         return 0;
0226
0227     if (capacity64 < (1ULL << 32)) {
0228         /*
0229          * Pick some standard mapping with at most 1024 cylinders, and
0230          * at most 62 sectors per track - this works up to 7905 MB.
0231          */
0232         ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
0233                (unsigned int *)ip + 0, (unsigned int *)ip + 1);
0234     }
0235
0236     /*
0237      * If something went wrong, then apparently we have to return a geometry
0238      * with more than 1024 cylinders.
0239      */
0240     if (ret || ip[0] > 255 || ip[1] > 63) {
0241         if ((capacity >> 11) > 65534) {
0242             ip[0] = 255;
0243             ip[1] = 63;
0244         } else {
0245             ip[0] = 64;
0246             ip[1] = 32;
0247         }
0248
0249         if (capacity > 65535*63*255)
0250             ip[2] = 65535;
0251         else
0252             ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
0253     }
0254
0255     return 0;
0256 }
0257 EXPORT_SYMBOL(scsicam_bios_param);