README 3.3 KB

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  1. This directory attempts to document the ABI between the Linux kernel and
  2. userspace, and the relative stability of these interfaces. Due to the
  3. everchanging nature of Linux, and the differing maturity levels, these
  4. interfaces should be used by userspace programs in different ways.
  5. We have four different levels of ABI stability, as shown by the four
  6. different subdirectories in this location. Interfaces may change levels
  7. of stability according to the rules described below.
  8. The different levels of stability are:
  9. stable/
  10. This directory documents the interfaces that the developer has
  11. defined to be stable. Userspace programs are free to use these
  12. interfaces with no restrictions, and backward compatibility for
  13. them will be guaranteed for at least 2 years. Most interfaces
  14. (like syscalls) are expected to never change and always be
  15. available.
  16. testing/
  17. This directory documents interfaces that are felt to be stable,
  18. as the main development of this interface has been completed.
  19. The interface can be changed to add new features, but the
  20. current interface will not break by doing this, unless grave
  21. errors or security problems are found in them. Userspace
  22. programs can start to rely on these interfaces, but they must be
  23. aware of changes that can occur before these interfaces move to
  24. be marked stable. Programs that use these interfaces are
  25. strongly encouraged to add their name to the description of
  26. these interfaces, so that the kernel developers can easily
  27. notify them if any changes occur (see the description of the
  28. layout of the files below for details on how to do this.)
  29. obsolete/
  30. This directory documents interfaces that are still remaining in
  31. the kernel, but are marked to be removed at some later point in
  32. time. The description of the interface will document the reason
  33. why it is obsolete and when it can be expected to be removed.
  34. The file Documentation/feature-removal-schedule.txt may describe
  35. some of these interfaces, giving a schedule for when they will
  36. be removed.
  37. removed/
  38. This directory contains a list of the old interfaces that have
  39. been removed from the kernel.
  40. Every file in these directories will contain the following information:
  41. What: Short description of the interface
  42. Date: Date created
  43. KernelVersion: Kernel version this feature first showed up in.
  44. Contact: Primary contact for this interface (may be a mailing list)
  45. Description: Long description of the interface and how to use it.
  46. Users: All users of this interface who wish to be notified when
  47. it changes. This is very important for interfaces in
  48. the "testing" stage, so that kernel developers can work
  49. with userspace developers to ensure that things do not
  50. break in ways that are unacceptable. It is also
  51. important to get feedback for these interfaces to make
  52. sure they are working in a proper way and do not need to
  53. be changed further.
  54. How things move between levels:
  55. Interfaces in stable may move to obsolete, as long as the proper
  56. notification is given.
  57. Interfaces may be removed from obsolete and the kernel as long as the
  58. documented amount of time has gone by.
  59. Interfaces in the testing state can move to the stable state when the
  60. developers feel they are finished. They cannot be removed from the
  61. kernel tree without going through the obsolete state first.
  62. It's up to the developer to place their interfaces in the category they
  63. wish for it to start out in.