€•.ß      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ+/translations/zh_CN/admin-guide/sysfs-rules”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/zh_TW/admin-guide/sysfs-rules”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/it_IT/admin-guide/sysfs-rules”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/ja_JP/admin-guide/sysfs-rules”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/ko_KR/admin-guide/sysfs-rules”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ+/translations/sp_SP/admin-guide/sysfs-rules”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒ+Rules on how to access information in sysfs”h]”hŒ+Rules on how to access information in sysfs”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒE/var/lib/git/docbuild/linux/Documentation/admin-guide/sysfs-rules.rst”h KubhŒ	paragraph”“”)”}”(hXJ  The kernel-exported sysfs exports internal kernel implementation details
and depends on internal kernel structures and layout. It is agreed upon
by the kernel developers that the Linux kernel does not provide a stable
internal API. Therefore, there are aspects of the sysfs interface that
may not be stable across kernel releases.”h]”hXJ  The kernel-exported sysfs exports internal kernel implementation details
and depends on internal kernel structures and layout. It is agreed upon
by the kernel developers that the Linux kernel does not provide a stable
internal API. Therefore, there are aspects of the sysfs interface that
may not be stable across kernel releases.”…””}”(hh¹hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hXª  To minimize the risk of breaking users of sysfs, which are in most cases
low-level userspace applications, with a new kernel release, the users
of sysfs must follow some rules to use an as-abstract-as-possible way to
access this filesystem. The current udev and HAL programs already
implement this and users are encouraged to plug, if possible, into the
abstractions these programs provide instead of accessing sysfs directly.”h]”hXª  To minimize the risk of breaking users of sysfs, which are in most cases
low-level userspace applications, with a new kernel release, the users
of sysfs must follow some rules to use an as-abstract-as-possible way to
access this filesystem. The current udev and HAL programs already
implement this and users are encouraged to plug, if possible, into the
abstractions these programs provide instead of accessing sysfs directly.”…””}”(hhÇhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K
hh£hžhubh¸)”}”(hŒ­But if you really do want or need to access sysfs directly, please follow
the following rules and then your programs should work with future
versions of the sysfs interface.”h]”hŒ­But if you really do want or need to access sysfs directly, please follow
the following rules and then your programs should work with future
versions of the sysfs interface.”…””}”(hhÕhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubhŒbullet_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hX  Do not use libsysfs
  It makes assumptions about sysfs which are not true. Its API does not
  offer any abstraction, it exposes all the kernel driver-core
  implementation details in its own API. Therefore it is not better than
  reading directories and opening the files yourself.
  Also, it is not actively maintained, in the sense of reflecting the
  current kernel development. The goal of providing a stable interface
  to sysfs has failed; it causes more problems than it solves. It
  violates many of the rules in this document.
”h]”hŒdefinition_list”“”)”}”(hhh]”hŒdefinition_list_item”“”)”}”(hX  Do not use libsysfs
It makes assumptions about sysfs which are not true. Its API does not
offer any abstraction, it exposes all the kernel driver-core
implementation details in its own API. Therefore it is not better than
reading directories and opening the files yourself.
Also, it is not actively maintained, in the sense of reflecting the
current kernel development. The goal of providing a stable interface
to sysfs has failed; it causes more problems than it solves. It
violates many of the rules in this document.
”h]”(hŒterm”“”)”}”(hŒDo not use libsysfs”h]”hŒDo not use libsysfs”…””}”(hhûhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h KhhõubhŒ
definition”“”)”}”(hhh]”h¸)”}”(hXó  It makes assumptions about sysfs which are not true. Its API does not
offer any abstraction, it exposes all the kernel driver-core
implementation details in its own API. Therefore it is not better than
reading directories and opening the files yourself.
Also, it is not actively maintained, in the sense of reflecting the
current kernel development. The goal of providing a stable interface
to sysfs has failed; it causes more problems than it solves. It
violates many of the rules in this document.”h]”hXó  It makes assumptions about sysfs which are not true. Its API does not
offer any abstraction, it exposes all the kernel driver-core
implementation details in its own API. Therefore it is not better than
reading directories and opening the files yourself.
Also, it is not actively maintained, in the sense of reflecting the
current kernel development. The goal of providing a stable interface
to sysfs has failed; it causes more problems than it solves. It
violates many of the rules in this document.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hhõubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h Khhðubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhhêubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hXq  sysfs is always at ``/sys``
  Parsing ``/proc/mounts`` is a waste of time. Other mount points are a
  system configuration bug you should not try to solve. For test cases,
  possibly support a ``SYSFS_PATH`` environment variable to overwrite the
  application's behavior, but never try to search for sysfs. Never try
  to mount it, if you are not an early boot script.
”h]”hï)”}”(hhh]”hô)”}”(hXg  sysfs is always at ``/sys``
Parsing ``/proc/mounts`` is a waste of time. Other mount points are a
system configuration bug you should not try to solve. For test cases,
possibly support a ``SYSFS_PATH`` environment variable to overwrite the
application's behavior, but never try to search for sysfs. Never try
to mount it, if you are not an early boot script.
”h]”(hú)”}”(hŒsysfs is always at ``/sys``”h]”(hŒsysfs is always at ”…””}”(hj?  hžhhŸNh NubhŒliteral”“”)”}”(hŒ``/sys``”h]”hŒ/sys”…””}”(hjI  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj?  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h K$hj;  ubj
  )”}”(hhh]”h¸)”}”(hXJ  Parsing ``/proc/mounts`` is a waste of time. Other mount points are a
system configuration bug you should not try to solve. For test cases,
possibly support a ``SYSFS_PATH`` environment variable to overwrite the
application's behavior, but never try to search for sysfs. Never try
to mount it, if you are not an early boot script.”h]”(hŒParsing ”…””}”(hj`  hžhhŸNh NubjH  )”}”(hŒ``/proc/mounts``”h]”hŒ/proc/mounts”…””}”(hjh  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj`  ubhŒ‡ is a waste of time. Other mount points are a
system configuration bug you should not try to solve. For test cases,
possibly support a ”…””}”(hj`  hžhhŸNh NubjH  )”}”(hŒ``SYSFS_PATH``”h]”hŒ
SYSFS_PATH”…””}”(hjz  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj`  ubhŒŸ environment variable to overwrite the
applicationâ€™s behavior, but never try to search for sysfs. Never try
to mount it, if you are not an early boot script.”…””}”(hj`  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K hj]  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj;  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h K$hj8  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhj4  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hX)	  devices are only "devices"
  There is no such thing like class-, bus-, physical devices,
  interfaces, and such that you can rely on in userspace. Everything is
  just simply a "device". Class-, bus-, physical, ... types are just
  kernel implementation details which should not be expected by
  applications that look for devices in sysfs.

  The properties of a device are:

  - devpath (``/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0``)

    - identical to the DEVPATH value in the event sent from the kernel
      at device creation and removal
    - the unique key to the device at that point in time
    - the kernel's path to the device directory without the leading
      ``/sys``, and always starting with a slash
    - all elements of a devpath must be real directories. Symlinks
      pointing to /sys/devices must always be resolved to their real
      target and the target path must be used to access the device.
      That way the devpath to the device matches the devpath of the
      kernel used at event time.
    - using or exposing symlink values as elements in a devpath string
      is a bug in the application

  - kernel name (``sda``, ``tty``, ``0000:00:1f.2``, ...)

    - a directory name, identical to the last element of the devpath
    - applications need to handle spaces and characters like ``!`` in
      the name

  - subsystem (``block``, ``tty``, ``pci``, ...)

    - simple string, never a path or a link
    - retrieved by reading the "subsystem"-link and using only the
      last element of the target path

  - driver (``tg3``, ``ata_piix``, ``uhci_hcd``)

    - a simple string, which may contain spaces, never a path or a
      link
    - it is retrieved by reading the "driver"-link and using only the
      last element of the target path
    - devices which do not have "driver"-link just do not have a
      driver; copying the driver value in a child device context is a
      bug in the application

  - attributes

    - the files in the device directory or files below subdirectories
      of the same device directory
    - accessing attributes reached by a symlink pointing to another device,
      like the "device"-link, is a bug in the application

  Everything else is just a kernel driver-core implementation detail
  that should not be assumed to be stable across kernel releases.
”h]”hï)”}”(hhh]”hô)”}”(hXÕ  devices are only "devices"
There is no such thing like class-, bus-, physical devices,
interfaces, and such that you can rely on in userspace. Everything is
just simply a "device". Class-, bus-, physical, ... types are just
kernel implementation details which should not be expected by
applications that look for devices in sysfs.

The properties of a device are:

- devpath (``/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0``)

  - identical to the DEVPATH value in the event sent from the kernel
    at device creation and removal
  - the unique key to the device at that point in time
  - the kernel's path to the device directory without the leading
    ``/sys``, and always starting with a slash
  - all elements of a devpath must be real directories. Symlinks
    pointing to /sys/devices must always be resolved to their real
    target and the target path must be used to access the device.
    That way the devpath to the device matches the devpath of the
    kernel used at event time.
  - using or exposing symlink values as elements in a devpath string
    is a bug in the application

- kernel name (``sda``, ``tty``, ``0000:00:1f.2``, ...)

  - a directory name, identical to the last element of the devpath
  - applications need to handle spaces and characters like ``!`` in
    the name

- subsystem (``block``, ``tty``, ``pci``, ...)

  - simple string, never a path or a link
  - retrieved by reading the "subsystem"-link and using only the
    last element of the target path

- driver (``tg3``, ``ata_piix``, ``uhci_hcd``)

  - a simple string, which may contain spaces, never a path or a
    link
  - it is retrieved by reading the "driver"-link and using only the
    last element of the target path
  - devices which do not have "driver"-link just do not have a
    driver; copying the driver value in a child device context is a
    bug in the application

- attributes

  - the files in the device directory or files below subdirectories
    of the same device directory
  - accessing attributes reached by a symlink pointing to another device,
    like the "device"-link, is a bug in the application

Everything else is just a kernel driver-core implementation detail
that should not be assumed to be stable across kernel releases.
”h]”(hú)”}”(hŒdevices are only "devices"”h]”hŒdevices are only â€œdevicesâ€”…””}”(hjµ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h K\hj±  ubj
  )”}”(hhh]”(h¸)”}”(hX/  There is no such thing like class-, bus-, physical devices,
interfaces, and such that you can rely on in userspace. Everything is
just simply a "device". Class-, bus-, physical, ... types are just
kernel implementation details which should not be expected by
applications that look for devices in sysfs.”h]”hX3  There is no such thing like class-, bus-, physical devices,
interfaces, and such that you can rely on in userspace. Everything is
just simply a â€œdeviceâ€. Class-, bus-, physical, ... types are just
kernel implementation details which should not be expected by
applications that look for devices in sysfs.”…””}”(hjÆ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K'hjÃ  ubh¸)”}”(hŒThe properties of a device are:”h]”hŒThe properties of a device are:”…””}”(hjÔ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K-hjÃ  ubhä)”}”(hhh]”(hé)”}”(hXÅ  devpath (``/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0``)

- identical to the DEVPATH value in the event sent from the kernel
  at device creation and removal
- the unique key to the device at that point in time
- the kernel's path to the device directory without the leading
  ``/sys``, and always starting with a slash
- all elements of a devpath must be real directories. Symlinks
  pointing to /sys/devices must always be resolved to their real
  target and the target path must be used to access the device.
  That way the devpath to the device matches the devpath of the
  kernel used at event time.
- using or exposing symlink values as elements in a devpath string
  is a bug in the application
”h]”(h¸)”}”(hŒ?devpath (``/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0``)”h]”(hŒ	devpath (”…””}”(hjé  hžhhŸNh NubjH  )”}”(hŒ5``/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0``”h]”hŒ1/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0”…””}”(hjñ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjé  ubhŒ)”…””}”(hjé  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K/hjå  ubhä)”}”(hhh]”(hé)”}”(hŒ_identical to the DEVPATH value in the event sent from the kernel
at device creation and removal”h]”h¸)”}”(hŒ_identical to the DEVPATH value in the event sent from the kernel
at device creation and removal”h]”hŒ_identical to the DEVPATH value in the event sent from the kernel
at device creation and removal”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K1hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubhé)”}”(hŒ2the unique key to the device at that point in time”h]”h¸)”}”(hj&  h]”hŒ2the unique key to the device at that point in time”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K3hj$  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubhé)”}”(hŒhthe kernel's path to the device directory without the leading
``/sys``, and always starting with a slash”h]”h¸)”}”(hŒhthe kernel's path to the device directory without the leading
``/sys``, and always starting with a slash”h]”(hŒ@the kernelâ€™s path to the device directory without the leading
”…””}”(hj?  hžhhŸNh NubjH  )”}”(hŒ``/sys``”h]”hŒ/sys”…””}”(hjG  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj?  ubhŒ", and always starting with a slash”…””}”(hj?  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K4hj;  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubhé)”}”(hX  all elements of a devpath must be real directories. Symlinks
pointing to /sys/devices must always be resolved to their real
target and the target path must be used to access the device.
That way the devpath to the device matches the devpath of the
kernel used at event time.”h]”h¸)”}”(hX  all elements of a devpath must be real directories. Symlinks
pointing to /sys/devices must always be resolved to their real
target and the target path must be used to access the device.
That way the devpath to the device matches the devpath of the
kernel used at event time.”h]”hX  all elements of a devpath must be real directories. Symlinks
pointing to /sys/devices must always be resolved to their real
target and the target path must be used to access the device.
That way the devpath to the device matches the devpath of the
kernel used at event time.”…””}”(hji  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K6hje  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubhé)”}”(hŒ]using or exposing symlink values as elements in a devpath string
is a bug in the application
”h]”h¸)”}”(hŒ\using or exposing symlink values as elements in a devpath string
is a bug in the application”h]”hŒ\using or exposing symlink values as elements in a devpath string
is a bug in the application”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K;hj}  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1hãhŸh¶h K1hjå  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhjâ  ubhé)”}”(hŒÅkernel name (``sda``, ``tty``, ``0000:00:1f.2``, ...)

- a directory name, identical to the last element of the devpath
- applications need to handle spaces and characters like ``!`` in
  the name
”h]”(h¸)”}”(hŒ5kernel name (``sda``, ``tty``, ``0000:00:1f.2``, ...)”h]”(hŒkernel name (”…””}”(hj§  hžhhŸNh NubjH  )”}”(hŒ``sda``”h]”hŒsda”…””}”(hj¯  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj§  ubhŒ, ”…””}”(hj§  hžhhŸNh NubjH  )”}”(hŒ``tty``”h]”hŒtty”…””}”(hjÁ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj§  ubhŒ, ”…””}”hj§  sbjH  )”}”(hŒ``0000:00:1f.2``”h]”hŒ0000:00:1f.2”…””}”(hjÓ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj§  ubhŒ, ...)”…””}”(hj§  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K>hj£  ubhä)”}”(hhh]”(hé)”}”(hŒ>a directory name, identical to the last element of the devpath”h]”h¸)”}”(hjð  h]”hŒ>a directory name, identical to the last element of the devpath”…””}”(hjò  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K@hjî  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhjë  ubhé)”}”(hŒIapplications need to handle spaces and characters like ``!`` in
the name
”h]”h¸)”}”(hŒHapplications need to handle spaces and characters like ``!`` in
the name”h]”(hŒ7applications need to handle spaces and characters like ”…””}”(hj	  hžhhŸNh NubjH  )”}”(hŒ``!``”h]”hŒ!”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj	  ubhŒ in
the name”…””}”(hj	  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KAhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhjë  ubeh}”(h]”h ]”h"]”h$]”h&]”j›  jœ  uh1hãhŸh¶h K@hj£  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhjâ  ubhé)”}”(hŒ·subsystem (``block``, ``tty``, ``pci``, ...)

- simple string, never a path or a link
- retrieved by reading the "subsystem"-link and using only the
  last element of the target path
”h]”(h¸)”}”(hŒ,subsystem (``block``, ``tty``, ``pci``, ...)”h]”(hŒsubsystem (”…””}”(hj?  hžhhŸNh NubjH  )”}”(hŒ	``block``”h]”hŒblock”…””}”(hjG  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj?  ubhŒ, ”…””}”(hj?  hžhhŸNh NubjH  )”}”(hŒ``tty``”h]”hŒtty”…””}”(hjY  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj?  ubhŒ, ”…””}”hj?  sbjH  )”}”(hŒ``pci``”h]”hŒpci”…””}”(hjk  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj?  ubhŒ, ...)”…””}”(hj?  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KDhj;  ubhä)”}”(hhh]”(hé)”}”(hŒ%simple string, never a path or a link”h]”h¸)”}”(hjˆ  h]”hŒ%simple string, never a path or a link”…””}”(hjŠ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KFhj†  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhjƒ  ubhé)”}”(hŒ]retrieved by reading the "subsystem"-link and using only the
last element of the target path
”h]”h¸)”}”(hŒ\retrieved by reading the "subsystem"-link and using only the
last element of the target path”h]”hŒ`retrieved by reading the â€œsubsystemâ€-link and using only the
last element of the target path”…””}”(hj¡  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KGhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhjƒ  ubeh}”(h]”h ]”h"]”h$]”h&]”j›  jœ  uh1hãhŸh¶h KFhj;  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhjâ  ubhé)”}”(hXp  driver (``tg3``, ``ata_piix``, ``uhci_hcd``)

- a simple string, which may contain spaces, never a path or a
  link
- it is retrieved by reading the "driver"-link and using only the
  last element of the target path
- devices which do not have "driver"-link just do not have a
  driver; copying the driver value in a child device context is a
  bug in the application
”h]”(h¸)”}”(hŒ,driver (``tg3``, ``ata_piix``, ``uhci_hcd``)”h]”(hŒdriver (”…””}”(hjÅ  hžhhŸNh NubjH  )”}”(hŒ``tg3``”h]”hŒtg3”…””}”(hjÍ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjÅ  ubhŒ, ”…””}”(hjÅ  hžhhŸNh NubjH  )”}”(hŒ``ata_piix``”h]”hŒata_piix”…””}”(hjß  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjÅ  ubhŒ, ”…””}”hjÅ  sbjH  )”}”(hŒ``uhci_hcd``”h]”hŒuhci_hcd”…””}”(hjñ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjÅ  ubhŒ)”…””}”(hjÅ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KJhjÁ  ubhä)”}”(hhh]”(hé)”}”(hŒAa simple string, which may contain spaces, never a path or a
link”h]”h¸)”}”(hŒAa simple string, which may contain spaces, never a path or a
link”h]”hŒAa simple string, which may contain spaces, never a path or a
link”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KLhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubhé)”}”(hŒ_it is retrieved by reading the "driver"-link and using only the
last element of the target path”h]”h¸)”}”(hŒ_it is retrieved by reading the "driver"-link and using only the
last element of the target path”h]”hŒcit is retrieved by reading the â€œdriverâ€-link and using only the
last element of the target path”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KNhj$  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubhé)”}”(hŒ’devices which do not have "driver"-link just do not have a
driver; copying the driver value in a child device context is a
bug in the application
”h]”h¸)”}”(hŒ‘devices which do not have "driver"-link just do not have a
driver; copying the driver value in a child device context is a
bug in the application”h]”hŒ•devices which do not have â€œdriverâ€-link just do not have a
driver; copying the driver value in a child device context is a
bug in the application”…””}”(hj@  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KPhj<  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj	  ubeh}”(h]”h ]”h"]”h$]”h&]”j›  jœ  uh1hãhŸh¶h KLhjÁ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhjâ  ubhé)”}”(hŒëattributes

- the files in the device directory or files below subdirectories
  of the same device directory
- accessing attributes reached by a symlink pointing to another device,
  like the "device"-link, is a bug in the application
”h]”(h¸)”}”(hŒ
attributes”h]”hŒ
attributes”…””}”(hjd  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KThj`  ubhä)”}”(hhh]”(hé)”}”(hŒ\the files in the device directory or files below subdirectories
of the same device directory”h]”h¸)”}”(hŒ\the files in the device directory or files below subdirectories
of the same device directory”h]”hŒ\the files in the device directory or files below subdirectories
of the same device directory”…””}”(hjy  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KVhju  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhjr  ubhé)”}”(hŒzaccessing attributes reached by a symlink pointing to another device,
like the "device"-link, is a bug in the application
”h]”h¸)”}”(hŒyaccessing attributes reached by a symlink pointing to another device,
like the "device"-link, is a bug in the application”h]”hŒ}accessing attributes reached by a symlink pointing to another device,
like the â€œdeviceâ€-link, is a bug in the application”…””}”(hj‘  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KXhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhjr  ubeh}”(h]”h ]”h"]”h$]”h&]”j›  jœ  uh1hãhŸh¶h KVhj`  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhjâ  ubeh}”(h]”h ]”h"]”h$]”h&]”j›  jœ  uh1hãhŸh¶h K/hjÃ  ubh¸)”}”(hŒ‚Everything else is just a kernel driver-core implementation detail
that should not be assumed to be stable across kernel releases.”h]”hŒ‚Everything else is just a kernel driver-core implementation detail
that should not be assumed to be stable across kernel releases.”…””}”(hj·  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K[hjÃ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj±  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h K\hj®  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhjª  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hX»  Properties of parent devices never belong into a child device.
  Always look at the parent devices themselves for determining device
  context properties. If the device ``eth0`` or ``sda`` does not have a
  "driver"-link, then this device does not have a driver. Its value is empty.
  Never copy any property of the parent-device into a child-device. Parent
  device properties may change dynamically without any notice to the
  child device.
”h]”hï)”}”(hhh]”hô)”}”(hX¯  Properties of parent devices never belong into a child device.
Always look at the parent devices themselves for determining device
context properties. If the device ``eth0`` or ``sda`` does not have a
"driver"-link, then this device does not have a driver. Its value is empty.
Never copy any property of the parent-device into a child-device. Parent
device properties may change dynamically without any notice to the
child device.
”h]”(hú)”}”(hŒ>Properties of parent devices never belong into a child device.”h]”hŒ>Properties of parent devices never belong into a child device.”…””}”(hjè  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h Kdhjä  ubj
  )”}”(hhh]”h¸)”}”(hXo  Always look at the parent devices themselves for determining device
context properties. If the device ``eth0`` or ``sda`` does not have a
"driver"-link, then this device does not have a driver. Its value is empty.
Never copy any property of the parent-device into a child-device. Parent
device properties may change dynamically without any notice to the
child device.”h]”(hŒfAlways look at the parent devices themselves for determining device
context properties. If the device ”…””}”(hjù  hžhhŸNh NubjH  )”}”(hŒ``eth0``”h]”hŒeth0”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjù  ubhŒ or ”…””}”(hjù  hžhhŸNh NubjH  )”}”(hŒ``sda``”h]”hŒsda”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjù  ubhŒú does not have a
â€œdriverâ€-link, then this device does not have a driver. Its value is empty.
Never copy any property of the parent-device into a child-device. Parent
device properties may change dynamically without any notice to the
child device.”…””}”(hjù  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K_hjö  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjä  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h Kdhjá  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhjÝ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hŒîHierarchy in a single device tree
  There is only one valid place in sysfs where hierarchy can be examined
  and this is below: ``/sys/devices.``
  It is planned that all device directories will end up in the tree
  below this directory.
”h]”hï)”}”(hhh]”hô)”}”(hŒæHierarchy in a single device tree
There is only one valid place in sysfs where hierarchy can be examined
and this is below: ``/sys/devices.``
It is planned that all device directories will end up in the tree
below this directory.
”h]”(hú)”}”(hŒ!Hierarchy in a single device tree”h]”hŒ!Hierarchy in a single device tree”…””}”(hjN  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h KjhjJ  ubj
  )”}”(hhh]”h¸)”}”(hŒÃThere is only one valid place in sysfs where hierarchy can be examined
and this is below: ``/sys/devices.``
It is planned that all device directories will end up in the tree
below this directory.”h]”(hŒZThere is only one valid place in sysfs where hierarchy can be examined
and this is below: ”…””}”(hj_  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices.``”h]”hŒ/sys/devices.”…””}”(hjg  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj_  ubhŒX
It is planned that all device directories will end up in the tree
below this directory.”…””}”(hj_  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kghj\  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjJ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h KjhjG  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhjC  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hXÖ  Classification by subsystem
  There are currently three places for classification of devices:
  ``/sys/block,`` ``/sys/class`` and ``/sys/bus.`` It is planned that these will
  not contain any device directories themselves, but only flat lists of
  symlinks pointing to the unified ``/sys/devices`` tree.
  All three places have completely different rules on how to access
  device information. It is planned to merge all three
  classification directories into one place at ``/sys/subsystem``,
  following the layout of the bus directories. All buses and
  classes, including the converted block subsystem, will show up
  there.
  The devices belonging to a subsystem will create a symlink in the
  "devices" directory at ``/sys/subsystem/<name>/devices``,

  If ``/sys/subsystem`` exists, ``/sys/bus``, ``/sys/class`` and ``/sys/block``
  can be ignored. If it does not exist, you always have to scan all three
  places, as the kernel is free to move a subsystem from one place to
  the other, as long as the devices are still reachable by the same
  subsystem name.

  Assuming ``/sys/class/<subsystem>`` and ``/sys/bus/<subsystem>``, or
  ``/sys/block`` and ``/sys/class/block`` are not interchangeable is a bug in
  the application.
”h]”hï)”}”(hhh]”hô)”}”(hX®  Classification by subsystem
There are currently three places for classification of devices:
``/sys/block,`` ``/sys/class`` and ``/sys/bus.`` It is planned that these will
not contain any device directories themselves, but only flat lists of
symlinks pointing to the unified ``/sys/devices`` tree.
All three places have completely different rules on how to access
device information. It is planned to merge all three
classification directories into one place at ``/sys/subsystem``,
following the layout of the bus directories. All buses and
classes, including the converted block subsystem, will show up
there.
The devices belonging to a subsystem will create a symlink in the
"devices" directory at ``/sys/subsystem/<name>/devices``,

If ``/sys/subsystem`` exists, ``/sys/bus``, ``/sys/class`` and ``/sys/block``
can be ignored. If it does not exist, you always have to scan all three
places, as the kernel is free to move a subsystem from one place to
the other, as long as the devices are still reachable by the same
subsystem name.

Assuming ``/sys/class/<subsystem>`` and ``/sys/bus/<subsystem>``, or
``/sys/block`` and ``/sys/class/block`` are not interchangeable is a bug in
the application.
”h]”(hú)”}”(hŒClassification by subsystem”h]”hŒClassification by subsystem”…””}”(hj¢  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h K‚hjž  ubj
  )”}”(hhh]”(h¸)”}”(hXÁ  There are currently three places for classification of devices:
``/sys/block,`` ``/sys/class`` and ``/sys/bus.`` It is planned that these will
not contain any device directories themselves, but only flat lists of
symlinks pointing to the unified ``/sys/devices`` tree.
All three places have completely different rules on how to access
device information. It is planned to merge all three
classification directories into one place at ``/sys/subsystem``,
following the layout of the bus directories. All buses and
classes, including the converted block subsystem, will show up
there.
The devices belonging to a subsystem will create a symlink in the
"devices" directory at ``/sys/subsystem/<name>/devices``,”h]”(hŒ@There are currently three places for classification of devices:
”…””}”(hj³  hžhhŸNh NubjH  )”}”(hŒ``/sys/block,``”h]”hŒ/sys/block,”…””}”(hj»  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj³  ubhŒ ”…””}”(hj³  hžhhŸNh NubjH  )”}”(hŒ``/sys/class``”h]”hŒ
/sys/class”…””}”(hjÍ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj³  ubhŒ and ”…””}”(hj³  hžhhŸNh NubjH  )”}”(hŒ``/sys/bus.``”h]”hŒ	/sys/bus.”…””}”(hjß  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj³  ubhŒ† It is planned that these will
not contain any device directories themselves, but only flat lists of
symlinks pointing to the unified ”…””}”(hj³  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices``”h]”hŒ/sys/devices”…””}”(hjñ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj³  ubhŒ« tree.
All three places have completely different rules on how to access
device information. It is planned to merge all three
classification directories into one place at ”…””}”(hj³  hžhhŸNh NubjH  )”}”(hŒ``/sys/subsystem``”h]”hŒ/sys/subsystem”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj³  ubhŒà,
following the layout of the bus directories. All buses and
classes, including the converted block subsystem, will show up
there.
The devices belonging to a subsystem will create a symlink in the
â€œdevicesâ€ directory at ”…””}”(hj³  hžhhŸNh NubjH  )”}”(hŒ!``/sys/subsystem/<name>/devices``”h]”hŒ/sys/subsystem/<name>/devices”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj³  ubhŒ,”…””}”(hj³  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kmhj°  ubh¸)”}”(hX+  If ``/sys/subsystem`` exists, ``/sys/bus``, ``/sys/class`` and ``/sys/block``
can be ignored. If it does not exist, you always have to scan all three
places, as the kernel is free to move a subsystem from one place to
the other, as long as the devices are still reachable by the same
subsystem name.”h]”(hŒIf ”…””}”(hj-  hžhhŸNh NubjH  )”}”(hŒ``/sys/subsystem``”h]”hŒ/sys/subsystem”…””}”(hj5  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj-  ubhŒ	 exists, ”…””}”(hj-  hžhhŸNh NubjH  )”}”(hŒ``/sys/bus``”h]”hŒ/sys/bus”…””}”(hjG  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj-  ubhŒ, ”…””}”(hj-  hžhhŸNh NubjH  )”}”(hŒ``/sys/class``”h]”hŒ
/sys/class”…””}”(hjY  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj-  ubhŒ and ”…””}”(hj-  hžhhŸNh NubjH  )”}”(hŒ``/sys/block``”h]”hŒ
/sys/block”…””}”(hjk  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj-  ubhŒÞ
can be ignored. If it does not exist, you always have to scan all three
places, as the kernel is free to move a subsystem from one place to
the other, as long as the devices are still reachable by the same
subsystem name.”…””}”(hj-  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kzhj°  ubh¸)”}”(hŒ¡Assuming ``/sys/class/<subsystem>`` and ``/sys/bus/<subsystem>``, or
``/sys/block`` and ``/sys/class/block`` are not interchangeable is a bug in
the application.”h]”(hŒ	Assuming ”…””}”(hjƒ  hžhhŸNh NubjH  )”}”(hŒ``/sys/class/<subsystem>``”h]”hŒ/sys/class/<subsystem>”…””}”(hj‹  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjƒ  ubhŒ and ”…””}”(hjƒ  hžhhŸNh NubjH  )”}”(hŒ``/sys/bus/<subsystem>``”h]”hŒ/sys/bus/<subsystem>”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjƒ  ubhŒ, or
”…””}”(hjƒ  hžhhŸNh NubjH  )”}”(hŒ``/sys/block``”h]”hŒ
/sys/block”…””}”(hj¯  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjƒ  ubhŒ and ”…””}”hjƒ  sbjH  )”}”(hŒ``/sys/class/block``”h]”hŒ/sys/class/block”…””}”(hjÁ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjƒ  ubhŒ5 are not interchangeable is a bug in
the application.”…””}”(hjƒ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K€hj°  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjž  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h K‚hj›  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhj—  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hX;  Block
  The converted block subsystem at ``/sys/class/block`` or
  ``/sys/subsystem/block`` will contain the links for disks and partitions
  at the same level, never in a hierarchy. Assuming the block subsystem to
  contain only disks and not partition devices in the same flat list is
  a bug in the application.
”h]”hï)”}”(hhh]”hô)”}”(hX1  Block
The converted block subsystem at ``/sys/class/block`` or
``/sys/subsystem/block`` will contain the links for disks and partitions
at the same level, never in a hierarchy. Assuming the block subsystem to
contain only disks and not partition devices in the same flat list is
a bug in the application.
”h]”(hú)”}”(hŒBlock”h]”hŒBlock”…””}”(hjü  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h K‰hjø  ubj
  )”}”(hhh]”h¸)”}”(hX*  The converted block subsystem at ``/sys/class/block`` or
``/sys/subsystem/block`` will contain the links for disks and partitions
at the same level, never in a hierarchy. Assuming the block subsystem to
contain only disks and not partition devices in the same flat list is
a bug in the application.”h]”(hŒ!The converted block subsystem at ”…””}”(hj  hžhhŸNh NubjH  )”}”(hŒ``/sys/class/block``”h]”hŒ/sys/class/block”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj  ubhŒ or
”…””}”(hj  hžhhŸNh NubjH  )”}”(hŒ``/sys/subsystem/block``”h]”hŒ/sys/subsystem/block”…””}”(hj'  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj  ubhŒÙ will contain the links for disks and partitions
at the same level, never in a hierarchy. Assuming the block subsystem to
contain only disks and not partition devices in the same flat list is
a bug in the application.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K…hj
  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjø  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h K‰hjõ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhjñ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hXY  "device"-link and <subsystem>:<kernel name>-links
  Never depend on the "device"-link. The "device"-link is a workaround
  for the old layout, where class devices are not created in
  ``/sys/devices/`` like the bus devices. If the link-resolving of a
  device directory does not end in ``/sys/devices/``, you can use the
  "device"-link to find the parent devices in ``/sys/devices/``, That is the
  single valid use of the "device"-link; it must never appear in any
  path as an element. Assuming the existence of the "device"-link for
  a device in ``/sys/devices/`` is a bug in the application.
  Accessing ``/sys/class/net/eth0/device`` is a bug in the application.

  Never depend on the class-specific links back to the ``/sys/class``
  directory.  These links are also a workaround for the design mistake
  that class devices are not created in ``/sys/devices.`` If a device
  directory does not contain directories for child devices, these links
  may be used to find the child devices in ``/sys/class.`` That is the single
  valid use of these links; they must never appear in any path as an
  element. Assuming the existence of these links for devices which are
  real child device directories in the ``/sys/devices`` tree is a bug in
  the application.

  It is planned to remove all these links when all class device
  directories live in ``/sys/devices.``
”h]”hï)”}”(hhh]”hô)”}”(hX1  "device"-link and <subsystem>:<kernel name>-links
Never depend on the "device"-link. The "device"-link is a workaround
for the old layout, where class devices are not created in
``/sys/devices/`` like the bus devices. If the link-resolving of a
device directory does not end in ``/sys/devices/``, you can use the
"device"-link to find the parent devices in ``/sys/devices/``, That is the
single valid use of the "device"-link; it must never appear in any
path as an element. Assuming the existence of the "device"-link for
a device in ``/sys/devices/`` is a bug in the application.
Accessing ``/sys/class/net/eth0/device`` is a bug in the application.

Never depend on the class-specific links back to the ``/sys/class``
directory.  These links are also a workaround for the design mistake
that class devices are not created in ``/sys/devices.`` If a device
directory does not contain directories for child devices, these links
may be used to find the child devices in ``/sys/class.`` That is the single
valid use of these links; they must never appear in any path as an
element. Assuming the existence of these links for devices which are
real child device directories in the ``/sys/devices`` tree is a bug in
the application.

It is planned to remove all these links when all class device
directories live in ``/sys/devices.``
”h]”(hú)”}”(hŒ1"device"-link and <subsystem>:<kernel name>-links”h]”hŒ5â€œdeviceâ€-link and <subsystem>:<kernel name>-links”…””}”(hjb  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h K¡hj^  ubj
  )”}”(hhh]”(h¸)”}”(hXY  Never depend on the "device"-link. The "device"-link is a workaround
for the old layout, where class devices are not created in
``/sys/devices/`` like the bus devices. If the link-resolving of a
device directory does not end in ``/sys/devices/``, you can use the
"device"-link to find the parent devices in ``/sys/devices/``, That is the
single valid use of the "device"-link; it must never appear in any
path as an element. Assuming the existence of the "device"-link for
a device in ``/sys/devices/`` is a bug in the application.
Accessing ``/sys/class/net/eth0/device`` is a bug in the application.”h]”(hŒˆNever depend on the â€œdeviceâ€-link. The â€œdeviceâ€-link is a workaround
for the old layout, where class devices are not created in
”…””}”(hjs  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices/``”h]”hŒ/sys/devices/”…””}”(hj{  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjs  ubhŒS like the bus devices. If the link-resolving of a
device directory does not end in ”…””}”(hjs  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices/``”h]”hŒ/sys/devices/”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjs  ubhŒB, you can use the
â€œdeviceâ€-link to find the parent devices in ”…””}”(hjs  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices/``”h]”hŒ/sys/devices/”…””}”(hjŸ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjs  ubhŒ©, That is the
single valid use of the â€œdeviceâ€-link; it must never appear in any
path as an element. Assuming the existence of the â€œdeviceâ€-link for
a device in ”…””}”(hjs  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices/``”h]”hŒ/sys/devices/”…””}”(hj±  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjs  ubhŒ( is a bug in the application.
Accessing ”…””}”(hjs  hžhhŸNh NubjH  )”}”(hŒ``/sys/class/net/eth0/device``”h]”hŒ/sys/class/net/eth0/device”…””}”(hjÃ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjs  ubhŒ is a bug in the application.”…””}”(hjs  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KŒhjp  ubh¸)”}”(hX>  Never depend on the class-specific links back to the ``/sys/class``
directory.  These links are also a workaround for the design mistake
that class devices are not created in ``/sys/devices.`` If a device
directory does not contain directories for child devices, these links
may be used to find the child devices in ``/sys/class.`` That is the single
valid use of these links; they must never appear in any path as an
element. Assuming the existence of these links for devices which are
real child device directories in the ``/sys/devices`` tree is a bug in
the application.”h]”(hŒ5Never depend on the class-specific links back to the ”…””}”(hjÛ  hžhhŸNh NubjH  )”}”(hŒ``/sys/class``”h]”hŒ
/sys/class”…””}”(hjã  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjÛ  ubhŒl
directory.  These links are also a workaround for the design mistake
that class devices are not created in ”…””}”(hjÛ  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices.``”h]”hŒ/sys/devices.”…””}”(hjõ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjÛ  ubhŒ| If a device
directory does not contain directories for child devices, these links
may be used to find the child devices in ”…””}”(hjÛ  hžhhŸNh NubjH  )”}”(hŒ``/sys/class.``”h]”hŒ/sys/class.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjÛ  ubhŒÁ That is the single
valid use of these links; they must never appear in any path as an
element. Assuming the existence of these links for devices which are
real child device directories in the ”…””}”(hjÛ  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices``”h]”hŒ/sys/devices”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hjÛ  ubhŒ" tree is a bug in
the application.”…””}”(hjÛ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K–hjp  ubh¸)”}”(hŒcIt is planned to remove all these links when all class device
directories live in ``/sys/devices.``”h]”(hŒRIt is planned to remove all these links when all class device
directories live in ”…””}”(hj1  hžhhŸNh NubjH  )”}”(hŒ``/sys/devices.``”h]”hŒ/sys/devices.”…””}”(hj9  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj1  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K hjp  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj^  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h K¡hj[  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhjW  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hX$  Position of devices along device chain can change.
  Never depend on a specific parent device position in the devpath,
  or the chain of parent devices. The kernel is free to insert devices into
  the chain. You must always request the parent device you are looking for
  by its subsystem value. You need to walk up the chain until you find
  the device that matches the expected subsystem. Depending on a specific
  position of a parent device or exposing relative paths using ``../`` to
  access the chain of parents is a bug in the application.
”h]”hï)”}”(hhh]”hô)”}”(hX  Position of devices along device chain can change.
Never depend on a specific parent device position in the devpath,
or the chain of parent devices. The kernel is free to insert devices into
the chain. You must always request the parent device you are looking for
by its subsystem value. You need to walk up the chain until you find
the device that matches the expected subsystem. Depending on a specific
position of a parent device or exposing relative paths using ``../`` to
access the chain of parents is a bug in the application.
”h]”(hú)”}”(hŒ2Position of devices along device chain can change.”h]”hŒ2Position of devices along device chain can change.”…””}”(hjp  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h Kªhjl  ubj
  )”}”(hhh]”h¸)”}”(hXâ  Never depend on a specific parent device position in the devpath,
or the chain of parent devices. The kernel is free to insert devices into
the chain. You must always request the parent device you are looking for
by its subsystem value. You need to walk up the chain until you find
the device that matches the expected subsystem. Depending on a specific
position of a parent device or exposing relative paths using ``../`` to
access the chain of parents is a bug in the application.”h]”(hXŸ  Never depend on a specific parent device position in the devpath,
or the chain of parent devices. The kernel is free to insert devices into
the chain. You must always request the parent device you are looking for
by its subsystem value. You need to walk up the chain until you find
the device that matches the expected subsystem. Depending on a specific
position of a parent device or exposing relative paths using ”…””}”(hj  hžhhŸNh NubjH  )”}”(hŒ``../``”h]”hŒ../”…””}”(hj‰  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj  ubhŒ< to
access the chain of parents is a bug in the application.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¤hj~  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjl  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h Kªhji  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhje  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubhé)”}”(hXÄ  When reading and writing sysfs device attribute files, avoid dependency
  on specific error codes wherever possible. This minimizes coupling to
  the error handling implementation within the kernel.

  In general, failures to read or write sysfs device attributes shall
  propagate errors wherever possible. Common errors include, but are not
  limited to:

      ``-EIO``: The read or store operation is not supported, typically
      returned by the sysfs system itself if the read or store pointer
      is ``NULL``.

      ``-ENXIO``: The read or store operation failed

  Error codes will not be changed without good reason, and should a change
  to error codes result in user-space breakage, it will be fixed, or the
  the offending change will be reverted.

  Userspace applications can, however, expect the format and contents of
  the attribute files to remain consistent in the absence of a version
  attribute change in the context of a given attribute.”h]”hï)”}”(hhh]”hô)”}”(hX¦  When reading and writing sysfs device attribute files, avoid dependency
on specific error codes wherever possible. This minimizes coupling to
the error handling implementation within the kernel.

In general, failures to read or write sysfs device attributes shall
propagate errors wherever possible. Common errors include, but are not
limited to:

    ``-EIO``: The read or store operation is not supported, typically
    returned by the sysfs system itself if the read or store pointer
    is ``NULL``.

    ``-ENXIO``: The read or store operation failed

Error codes will not be changed without good reason, and should a change
to error codes result in user-space breakage, it will be fixed, or the
the offending change will be reverted.

Userspace applications can, however, expect the format and contents of
the attribute files to remain consistent in the absence of a version
attribute change in the context of a given attribute.”h]”(hú)”}”(hŒGWhen reading and writing sysfs device attribute files, avoid dependency”h]”hŒGWhen reading and writing sysfs device attribute files, avoid dependency”…””}”(hjÄ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùhŸh¶h K¿hjÀ  ubj
  )”}”(hhh]”(h¸)”}”(hŒzon specific error codes wherever possible. This minimizes coupling to
the error handling implementation within the kernel.”h]”hŒzon specific error codes wherever possible. This minimizes coupling to
the error handling implementation within the kernel.”…””}”(hjÕ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K­hjÒ  ubh¸)”}”(hŒ–In general, failures to read or write sysfs device attributes shall
propagate errors wherever possible. Common errors include, but are not
limited to:”h]”hŒ–In general, failures to read or write sysfs device attributes shall
propagate errors wherever possible. Common errors include, but are not
limited to:”…””}”(hjã  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K°hjÒ  ubhŒblock_quote”“”)”}”(hŒÀ``-EIO``: The read or store operation is not supported, typically
returned by the sysfs system itself if the read or store pointer
is ``NULL``.

``-ENXIO``: The read or store operation failed
”h]”(h¸)”}”(hŒ``-EIO``: The read or store operation is not supported, typically
returned by the sysfs system itself if the read or store pointer
is ``NULL``.”h]”(jH  )”}”(hŒ``-EIO``”h]”hŒ-EIO”…””}”(hjû  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj÷  ubhŒ~: The read or store operation is not supported, typically
returned by the sysfs system itself if the read or store pointer
is ”…””}”(hj÷  hžhhŸNh NubjH  )”}”(hŒ``NULL``”h]”hŒNULL”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj÷  ubhŒ.”…””}”(hj÷  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K´hjó  ubh¸)”}”(hŒ.``-ENXIO``: The read or store operation failed”h]”(jH  )”}”(hŒ
``-ENXIO``”h]”hŒ-ENXIO”…””}”(hj)	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jG  hj%	  ubhŒ$: The read or store operation failed”…””}”(hj%	  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¸hjó  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jñ  hŸh¶h K´hjÒ  ubh¸)”}”(hŒ¶Error codes will not be changed without good reason, and should a change
to error codes result in user-space breakage, it will be fixed, or the
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to error codes result in user-space breakage, it will be fixed, or the
the offending change will be reverted.”…””}”(hjG	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KºhjÒ  ubh¸)”}”(hŒÁUserspace applications can, however, expect the format and contents of
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attribute change in the context of a given attribute.”…””}”(hjU	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¾hjÒ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjÀ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóhŸh¶h K¿hj½  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhj¹  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhhåhžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”j›  jœ  uh1hãhŸh¶h Khh£hžhubeh}”(h]”Œ+rules-on-how-to-access-information-in-sysfs”ah ]”h"]”Œ+rules on how to access information in sysfs”ah$]”h&]”uh1h¡hhhžhhŸh¶h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h¶uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¦NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
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