linear.rst 1.5 KB

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  1. =========
  2. dm-linear
  3. =========
  4. Device-Mapper's "linear" target maps a linear range of the Device-Mapper
  5. device onto a linear range of another device. This is the basic building
  6. block of logical volume managers.
  7. Parameters: <dev path> <offset>
  8. <dev path>:
  9. Full pathname to the underlying block-device, or a
  10. "major:minor" device-number.
  11. <offset>:
  12. Starting sector within the device.
  13. Example scripts
  14. ===============
  15. ::
  16. #!/bin/sh
  17. # Create an identity mapping for a device
  18. echo "0 `blockdev --getsz $1` linear $1 0" | dmsetup create identity
  19. ::
  20. #!/bin/sh
  21. # Join 2 devices together
  22. size1=`blockdev --getsz $1`
  23. size2=`blockdev --getsz $2`
  24. echo "0 $size1 linear $1 0
  25. $size1 $size2 linear $2 0" | dmsetup create joined
  26. ::
  27. #!/usr/bin/perl -w
  28. # Split a device into 4M chunks and then join them together in reverse order.
  29. my $name = "reverse";
  30. my $extent_size = 4 * 1024 * 2;
  31. my $dev = $ARGV[0];
  32. my $table = "";
  33. my $count = 0;
  34. if (!defined($dev)) {
  35. die("Please specify a device.\n");
  36. }
  37. my $dev_size = `blockdev --getsz $dev`;
  38. my $extents = int($dev_size / $extent_size) -
  39. (($dev_size % $extent_size) ? 1 : 0);
  40. while ($extents > 0) {
  41. my $this_start = $count * $extent_size;
  42. $extents--;
  43. $count++;
  44. my $this_offset = $extents * $extent_size;
  45. $table .= "$this_start $extent_size linear $dev $this_offset\n";
  46. }
  47. `echo \"$table\" | dmsetup create $name`;