dospartlibata.c

vxworks 下ata,scsi,以及IO口的 操作事例程序 对文件系统编程很有帮助

/* dosPartLibAta.c - show & mount ATA HDD MSDOS partitions */
 
 
 /*
 modification history
 --------------------
 01c,15sep97,jkf   removed LCHS support.  Only useful for MSDOS versions
                   before 3.3, not likely anyone needs LCHS support.  
                   Added support for big endian arches and arches without
                   dynamic bus sizing, which involved byte swapping macro
                   and reading sector data with macro offsets. Now supports
                   80x86, 68k, SPARC, MIPS, PPC, i960, etc.)  Revised docs.
 01b,01sep97,jkf   fixed check for LBA support in dosPartRdLbaAta().
                   fixed stdlib.h filename case for Unix.
                   fixed args to ataDevCreate in example comments.
                   fixed cosmetics in sector and show routines.  
 01a,01sep97,jkf   written.
 */
 
 
 /*
 DESCRIPTION:
 This library is provided by Wind River Systems Customer
 Support strictly as an educational example.
 
 This code supports both mounting and displaying partition 
 tables written by MSDOS FDISK.exe or by any other MSDOS 
 FDISK.exe compatible partitioning software.  
 
 The first partition table is contained within a hard drives
 Master Boot Record (MBR) sector, which is defined as sector
 one, cylinder zero, head zero or logical block address zero.
 The mounting and displaying routines within this code will 
 first parse the MBR partition tables entries (defined below)
 and also recursively parse any "extended" partition tables,
 which may reside within another Cylinder, Head, and Sector 
 (CHS) combination further into the hard disk.   (Also known
 as extended partition tables chained from the MBR's partition
 table.  MSDOS file systems within extended partitions are known
 to those familiar with the MSDOS FDISK.exe utility as "Logical 
 drives within the extended partition".
 
 Since MSDOS file systems have a fixed number of clusters, 64Kb,
 and clusters are the minimum allocation unit at the file system
 level, using partitions can help optimize cluster size for a given
 hard disk,  improving performance and resource usage.  For example, 
 a 1-gigabyte hard disk with a single MSDOS file system has the 
 following minimum allocation unit at the dosFsLib open/read/write
 level interface:
 
     1GB/64KB = Minimum allocation unit.
 
 This may produce a minimum allocation unit that is larger than
 what the developer desires (for cluster boundary buffer alignment,
 or other buffering, ect).
 
 One solution is to sub-divide the disk into smaller partitions
 or "logical disks" on the single physical disk and format file 
 systems over each of the partitions.  (Then using this code you
 may mount them.)   If you used four equal sized partitions, then
 this method produces:
 
     256MB/64KB = Minimum allocation unit.	
     256MB/64KB = Minimum allocation unit.
     256MB/64KB = Minimum allocation unit.
     256MB/64KB = Minimum allocation unit.
 
 This produces a smaller minimum allocation unit and may be 
 better suited for optimal application file system performance.
 Each partition contains its own unique file system.  As far
 as the file system level is concerned it is on a unique disk.
 
 Here is a picture showing the layout of a single disk containing
 multiple MSDOS file systems:
 
 (Note, all ASCII pictures herein are best viewed with
  an 'equally sized characters' or 'fixed width' style font)
 
   +---------------------------------------------------------+
   |<---------------------The entire disk------------------->|
   |M                                                        |
   |B<---C:--->                                              |
   |R           /---- First extended partition--------------\|
   |           E<---D:---><-Rest of the ext part------------>|
   |P          x                                             |
   |A          t          E<---E:--->E<Rest of the ext part->|
   |R                     x          x                       |
   |T                     t          t<---------F:---------->|
   +---------------------------------------------------------+
   (Ext == extended partition sector)
 
 
 A MS-DOS partition table resides within one sector on a hard
 disk.  There is always one in the first sector of a hard disk
 partitioned with FDISK.exe.  There first partition table may
 contain references to "extended" partition tables residing on
 other sectors if there are multiple partitions.  The first 
 sector of the disk is the starting point.  Partition tables
 are of the format:
 
 Offset from     
 the beginning 
 of the sector          Description
 -------------          -------------------------
    0x1be               Partition 1 table entry  (16 bytes)
    0x1ce               Partition 2 table entry  (16 bytes)
    0x1de               Partition 3 table entry  (16 bytes)
    0x1ee               Partition 4 table entry  (16 bytes)
    0x1fe               Signature  (0x55aa, 2 bytes)
 
 
 Individual MSDOS partition table entries are of the format:
 
 Offset   Size      Description
 ------   ----      ------------------------------
  0x0     8 bits    boot type
  0x1     8 bits    beginning sector head value
  0x2     8 bits    beginning sector (2 high bits of cylinder#)
  0x3     8 bits    beginning cylinder# (low order bits of cylinder#)
  0x4     8 bits    system indicator
  0x5     8 bits    ending sector head value
  0x6     8 bits    ending sector (2 high bits of cylinder#)
  0x7     8 bits    ending cylinder# (low order bits of cylinder#)
  0x8    32 bits    number of sectors preceding the partition
  0xc    32 bits    number of sectors in the partition
   
 In the partition table entry, the Sector/Cylinder (16bits)
 (offset 0x2 & 0x3) fields data are stored in the format:
 
  |7|6|5|4|3|2|1|0|  The first 8 bits of offset 0x2.
   | | `------------ 6 least significant bit's contain the sector 
   | |               offset within cylinder.  sector == 6 bits.
   | |
   `-`-------------- Two most significant (high order) bits of the 
                     cylinder value.
 
  |7|6|5|4|3|2|1|0|  2nd 8 bits  (cylinder 0x3)
   `---------------- Eight least significant (low order) bits of the
                     cylinder value.
 
 This format restricts partition entries to 10 cylinder bits & 6 sector
 bits and 8 head bits.  This is also the format used by the PC-AT BIOS
 Int13h functions, which is used by FDISK.exe 
 
 dosPartLibAta/Scsi.c uses the following method of parsing the CHS values
 stored in the 0x2 & 0x3 partition table offsets into distinct values:
 
 Cyl = ((((dospt_startSec) & 0x00c0) << 2) |
        (((dospt_startSec) & 0xff00) >> 8));
 
 Hd  = pPartTbl->dospt_startHead;
 
 Sec = (pPartTbl->dospt_startSec & 0x003f); 
 
 (see DOS_PART_TBL struct typedef in dosFsLib.h)
 
 This produces individual CHS value from the values that
 are contained within the MSDOS partition table entry.  
 
 Definitions of CHS terms:
 
 CHS - Cylinder/Head/Sector. 
 
 L-CHS - Logical - CHS (used by INT 13 AxH/FDISK.exe) 
         256 heads, 1024 cylinders, 63 sectors. max.
         LCHS allow ~8.4 GB addressable space.
 
 P-CHS - Physical CHS (used by physical ATA device) 
         16 heads, 65535 cylinders, 63 sectors.
         PCHS allow ~137GB addressable space.
         (VxWorks ataRawio() uses PCHS)
 
 LBA - Logical Block Address. ATA/SCSI absolute sector
       numbering scheme.  LBA sector 0 == addresses the
       first sector on a device by definition.  ATA devices
       may also support LBA at the device interface. ATA
       standard says that cylinder 0, head 0, sector 1 == LBA 0.
       LBA allows (~137GB) on an ATA device. 
 
 The  MSDOS "logical CHS" (LCHS) format combined with the 
 Physical IDE/ATA CHS interface (PCHS) gives MSDOS the 
 following addressing limitation:
 
                   +------------+----------+----------------+   
                   | BIOS INT13 | IDE/ATA  | Combined Limit |
 +-----------------+------------+----------+----------------+   
 |Max Sectors/Track|  63        |    255   |     63         |
 +-----------------+------------+----------+----------------+
 |Max Heads        |  256       |     16   |     16         |
 +-----------------+------------+----------+----------------+
 |Max Cylinders    |  1024      |  65536   |    1024        |
 +-----------------+------------+----------+----------------+
 |Capacity         |  8.4GB     |  136.9GB |   528 MB       |
 +-----------------+------------+----------+----------------+
 
 1024 x 16 x 63 X 512 bytes/sector = 528.48 MB limit.
 
 Cylinder bits : 10 = 1024
 Head bits     :  4 = 16
 Sector bits   :  6 (-1) = 63 
 
 (by convention, CHS sector numbering begins at
  #1, not #0; LBA begins at zero, which is CHS#1) 
 
 To overcome the limitation. PC BIOS/OS vendors perform what is often
 referred to as geometric or "drive" CHS translation to address more 
 than 528MB, and to "address" cylinders above 1024.
 
 BIOS vendors offer CHS translation extensions that are based
 around the format of the PC-AT BIOS call "INT 0x13 function 0x8"
 aka "Get Current Drive Parameters"  There are also two parameter
 tables EDPT and FDPT set by the BIOS interfaces.  EDPT is sometimes
 not supported depending on the system BIOS.  The FDPT is always 
 supported on PC-AT compatible BIOS.  Code is available for the x86
 VxWorks BSP to call INT13h F8h romInit.s BIOS call, which returns
 the FDPT.  This is not needed when using LBA on newer systems.
 It is possible in the pc486/pc386 VxWorks BSP's to make an
 BIOS (INT13h F8H) call in romInit.s before the switch to 
 protected mode.  Sample romInit.s code demonstrating this 
 will be provided upon request, contact [e-mail].
 requesting "Int13h romInit.s x86 code".
 
 There exists also some 3rd party software based disk overlay
 programs (Such as OnTrack's Disk Manager,TM.) which uses a
 semi-proprietary strategy to support drives over 528MB.  
 
 In most cases, the translated LCHS geometry is applied such that
 all sectors are addressed at the same physical location as when
 the drive is used within an untranslated environment.  However,
 not in all cases, and then there is a breakdown.  Alas, there 
 is not any standard for defining the altered geometry translation
 scheme, so compatibility issues will arise when moving drives from
 one BIOS, Operating System, driver, and/or controller to another.
 
 VxWorks SCSI and ATA drivers communicate directly with the
 controller and do not use the BIOS.  The VxWorks ATA driver
 may address the full 136.9GB offered by ATA, and the full range
 offered by SCSI.  So this is not an issue for VxWorks.  It should
 be noted however, since all the partition table data will be stored 
 in LCHS format.
 
 Here is an example of a typical PCHS to LCHS translation.
 
 (Note, all ASCII pictures herein are best viewed with
  an 'equally sized characters'/'fixed width' style font)
 
 +----------------+------------+----------------+-------------+--------+
 |Actual Cylinders|Actual Heads|Altered Cylinder|Altered Heads|Max Size|
 +----------------+------------+----------------+-------------+--------+
 |  1<C<=1024     | 1<H<=16    |     C=C        |    H=H      |528 MB  |
 +----------------+------------+----------------+-------------+--------+
 | 1024<C<=2048   | 1<H<=16    |     C=C/2      |    H=H*2    |  1GB   |
 +----------------+------------+----------------+-------------+--------+
 | 2048<C<=4096   | 1<H<=16    |     C=C/4      |    H=H*4    | 2.1GB  |
 +----------------+------------+----------------+-------------+--------+
 | 4096<C<=8192   | 1<H<=16    |     C=C/8      |    H=H*8    | 4.2GB  |
 +----------------+------------+----------------+-------------+--------+
 | 8192<C<=16384  | 1<H<=16    |     C=C/16     |    H=H*16   | 8.4GB  |
 +----------------+------------+----------------+-------------+--------+
 | 16384<C<=32768 | 1<H<=8     |     C=C/32     |    H=H*32   | 8.4GB  |
 +----------------+------------+----------------+-------------+--------+
 | 32768<C<=65536 | 1<H<=4     |     C=C/64     |    H=H*64   | 8.4GB  |
 +----------------+------------+----------------+-------------+--------+
 
 
 Another type of translation always sets the sectors to 63, 
 this produces different geometry than the above.
 
 +----------------+----------+---------+--------------+
 |Range           | Sectors  | Heads   | Cylinders    |
 +----------------+----------+---------+--------------+
 |  1<X<=528MB    |   63     |  16     | X/(63*16*512)|
 +----------------+----------+---------+--------------+
 | 528MB<X<=1GB   |   63     |  32     | X/(63*32*512)|
 +----------------+----------+---------+--------------+
 | 1GB<X<=2.1GB   |   63     |  64     | X/(63*64*512)|
 +----------------+----------+---------+--------------+
 | 2.1GB<X<=4.2GB |   63     |  128    |X/(63*128*512)|
 +----------------+----------+---------+--------------+
 | 4.2GB<X<=8.4GB |   63     |  256    |X/(63*255*512)|
 +----------------+----------+---------+--------------+
 
 There are several MSDOS utilities (from Phoenix, and Western 
 Digital, and more, such as wdtblchk.exe, and chkbios.exe) which
 can be used on PC's to check translations.  These utilities
 use BIOS calls to read the EPDT and FPDT to determine the PCHS
 and LCHS and LBA values for a given system.  
 
 TRANSLATION ALGORITHMS:
 ----------------------
 
 The algorithm used in this code for LBA to PCHS translation 
 (in dosPartRdLba[Ata/Scsi]) is:
         
 PCHS_cylinder = LBA / (heads_per_cylinder * sectors_per_track)
          temp = LBA % (heads_per_cylinder * sectors_per_track)
 PCHS_head     = temp / sectors_per_track
 PCHS_sector   = temp % sectors_per_track + 1
 
 
 The reverse, PCHS to LBA, is not implement but shown here