shoelace源代码分析之disktab

下面是disktab.doc文件中的一部分说明

The following entries are used:

     Name Type Description
     se  num  Number of bytes per sector
     ns  num  Number of sectors per track
     nt  num  Number of tracks per cylinder
     md  num  Media description byte
     fp  str  Floppy parameter table

下面是/etc/disktab文件

#| Floppy disks
#|
#| 5.25 inch double sided double density 360kb disks
f0|5.25dsdd|5.25 inch double sided double density 360kb disks:\
    :nt#2:se#512:ns#9:md#253:\
    :fp=0xdf 0x2 0x25 0x2 0x9 0x2a 0xff 0x50 0xf6 0x1 0x8:
#|
#| 5.25 inch double sided quad density 720kb disks
f1|5.25dsqd|5.25 inch double sided quad density 720kb disks:\
    :nt#2:se#512:ns#9:md#240:\
    :fp=0xdf 0x2 0x25 0x2 0x9 0x2a 0xff 0x50 0xf6 0x1 0x8:
#|
#| 3.5 inch double sided double density 720kb disks
#| duplicated from 5.25dsqd - this seems to work
f2|3.5dsdd|3.5 inch double sided double density 720kb disks:\
    :nt#2:se#512:ns#9:md#240:\
    :fp=0xdf 0x2 0x25 0x2 0x9 0x2a 0xff 0x50 0xf6 0x1 0x8:
#|
#| 5.25 inch double sided high density 1200kb disks
f3|5.25dshd|5.25 inch double sided high density 1200kb disks:\
    :nt#2:se#512:ns#15:md#249:\
    :fp=0xdf 0x2 0x25 0x2 0xf 0x1b 0xff 0x54 0xf6 0x1 0x8:
#|
#|
#| Generic hard disk
#|
#| Hard disk parameters are obtained from the controller
#| at boot time. These values are dummy values to make
#| the installation procedure the same for both hard
#| and soft disks.
w0|wini|Generic hard disk:\
    :nt#0:se#512:ns#0:md#248:\
    :fp=0 0 0 0 0 0 0 0 0 0 0:

可见对于硬盘来说，shoelace支持的硬盘有一些限制：se为512既是每扇区为512字节。

下面是laceup.c文件中和disktab文件相关的代码：

  disktabfilename = findfile(DISKTABFILE);

  if ((fake_env[0] = (char *) malloc(sizeof(termcapenv)-1 +
                     strlen(disktabfilename) + 1)) == 0) {
    fputs("No room for termcap environment entry\n", stderr);
    exit(1);
  }
  strcpy(fake_env[0], termcapenv);
  strcat(fake_env[0], disktabfilename);
  environ = &fake_env[0];
  switch (tgetent(disktab, disktype)) {
  case 0:
    fprintf(stderr, "Disk type %s not found in %s\n",
            disktype, strchr(fake_env[0], '=')+1);
    exit(1);
  case -1:
    fprintf(stderr, "%s not found\n", strchr(fake_env[0], '=')+1);
    exit(1);
  }