€•ð†      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/process/stable-api-nonsense”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$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ//translations/zh_TW/process/stable-api-nonsense”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ//translations/it_IT/process/stable-api-nonsense”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ//translations/ja_JP/process/stable-api-nonsense”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ//translations/ko_KR/process/stable-api-nonsense”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ//translations/sp_SP/process/stable-api-nonsense”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒtarget”“”)”}”(hŒ.. _stable_api_nonsense:”h]”h}”(h]”h ]”h"]”h$]”h&]”Œrefid”Œstable-api-nonsense”uh1h¡h KhhhžhhŸŒI/var/lib/git/docbuild/linux/Documentation/process/stable-api-nonsense.rst”ubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒ!The Linux Kernel Driver Interface”h]”hŒ!The Linux Kernel Driver Interface”…””}”(hh·hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hµhh²hžhhŸh¯h KubhŒ	paragraph”“”)”}”(hŒ.(all of your questions answered and then some)”h]”hŒ.(all of your questions answered and then some)”…””}”(hhÇhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Khh²hžhubhÆ)”}”(hŒ#Greg Kroah-Hartman <greg@kroah.com>”h]”(hŒGreg Kroah-Hartman <”…””}”(hhÕhžhhŸNh NubhŒ	reference”“”)”}”(hŒgreg@kroah.com”h]”hŒgreg@kroah.com”…””}”(hhßhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”Œmailto:greg@kroah.com”uh1hÝhhÕubhŒ>”…””}”(hhÕhžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Khh²hžhubhÆ)”}”(hŒŠThis is being written to try to explain why Linux **does not have a binary
kernel interface, nor does it have a stable kernel interface**.”h]”(hŒ2This is being written to try to explain why Linux ”…””}”(hhùhžhhŸNh NubhŒstrong”“”)”}”(hŒW**does not have a binary
kernel interface, nor does it have a stable kernel interface**”h]”hŒSdoes not have a binary
kernel interface, nor does it have a stable kernel interface”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hhùubhŒ.”…””}”(hhùhžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K
hh²hžhubhŒnote”“”)”}”(hXð  Please realize that this article describes the **in kernel** interfaces, not
the kernel to userspace interfaces.

The kernel to userspace interface is the one that application programs use,
the syscall interface.  That interface is **very** stable over time, and
will not break.  I have old programs that were built on a pre 0.9something
kernel that still work just fine on the latest 2.6 kernel release.
That interface is the one that users and application programmers can count
on being stable.”h]”(hÆ)”}”(hŒpPlease realize that this article describes the **in kernel** interfaces, not
the kernel to userspace interfaces.”h]”(hŒ/Please realize that this article describes the ”…””}”(hj!  hžhhŸNh Nubj  )”}”(hŒ**in kernel**”h]”hŒ	in kernel”…””}”(hj)  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj!  ubhŒ4 interfaces, not
the kernel to userspace interfaces.”…””}”(hj!  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Khj  ubhÆ)”}”(hX~  The kernel to userspace interface is the one that application programs use,
the syscall interface.  That interface is **very** stable over time, and
will not break.  I have old programs that were built on a pre 0.9something
kernel that still work just fine on the latest 2.6 kernel release.
That interface is the one that users and application programmers can count
on being stable.”h]”(hŒvThe kernel to userspace interface is the one that application programs use,
the syscall interface.  That interface is ”…””}”(hjA  hžhhŸNh Nubj  )”}”(hŒ**very**”h]”hŒvery”…””}”(hjI  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjA  ubhX    stable over time, and
will not break.  I have old programs that were built on a pre 0.9something
kernel that still work just fine on the latest 2.6 kernel release.
That interface is the one that users and application programmers can count
on being stable.”…””}”(hjA  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Khj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  hh²hžhhŸh¯h Nubh±)”}”(hhh]”(h¶)”}”(hŒExecutive Summary”h]”hŒExecutive Summary”…””}”(hjj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hµhjg  hžhhŸh¯h KubhÆ)”}”(hX®  You think you want a stable kernel interface, but you really do not, and
you don't even know it.  What you want is a stable running driver, and
you get that only if your driver is in the main kernel tree.  You also
get lots of other good benefits if your driver is in the main kernel
tree, all of which has made Linux into such a strong, stable, and mature
operating system which is the reason you are using it in the first
place.”h]”hX°  You think you want a stable kernel interface, but you really do not, and
you donâ€™t even know it.  What you want is a stable running driver, and
you get that only if your driver is in the main kernel tree.  You also
get lots of other good benefits if your driver is in the main kernel
tree, all of which has made Linux into such a strong, stable, and mature
operating system which is the reason you are using it in the first
place.”…””}”(hjx  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Khjg  hžhubeh}”(h]”Œexecutive-summary”ah ]”h"]”Œexecutive summary”ah$]”h&]”uh1h°hh²hžhhŸh¯h Kubh±)”}”(hhh]”(h¶)”}”(hŒIntro”h]”hŒIntro”…””}”(hj‘  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hµhjŽ  hžhhŸh¯h K&ubhÆ)”}”(hŒÛIt's only the odd person who wants to write a kernel driver that needs
to worry about the in-kernel interfaces changing.  For the majority of
the world, they neither see this interface, nor do they care about it at
all.”h]”hŒÝItâ€™s only the odd person who wants to write a kernel driver that needs
to worry about the in-kernel interfaces changing.  For the majority of
the world, they neither see this interface, nor do they care about it at
all.”…””}”(hjŸ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K(hjŽ  hžhubhÆ)”}”(hXà  First off, I'm not going to address **any** legal issues about closed
source, hidden source, binary blobs, source wrappers, or any other term
that describes kernel drivers that do not have their source code
released under the GPL.  Please consult a lawyer if you have any legal
questions, I'm a programmer and hence, I'm just going to be describing
the technical issues here (not to make light of the legal issues, they
are real, and you do need to be aware of them at all times.)”h]”(hŒ&First off, Iâ€™m not going to address ”…””}”(hj­  hžhhŸNh Nubj  )”}”(hŒ**any**”h]”hŒany”…””}”(hjµ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj­  ubhX¹   legal issues about closed
source, hidden source, binary blobs, source wrappers, or any other term
that describes kernel drivers that do not have their source code
released under the GPL.  Please consult a lawyer if you have any legal
questions, Iâ€™m a programmer and hence, Iâ€™m just going to be describing
the technical issues here (not to make light of the legal issues, they
are real, and you do need to be aware of them at all times.)”…””}”(hj­  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K-hjŽ  hžhubhÆ)”}”(hŒÇSo, there are two main topics here, binary kernel interfaces and stable
kernel source interfaces.  They both depend on each other, but we will
discuss the binary stuff first to get it out of the way.”h]”hŒÇSo, there are two main topics here, binary kernel interfaces and stable
kernel source interfaces.  They both depend on each other, but we will
discuss the binary stuff first to get it out of the way.”…””}”(hjÍ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K5hjŽ  hžhubeh}”(h]”Œintro”ah ]”h"]”Œintro”ah$]”h&]”uh1h°hh²hžhhŸh¯h K&ubh±)”}”(hhh]”(h¶)”}”(hŒBinary Kernel Interface”h]”hŒBinary Kernel Interface”…””}”(hjæ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hµhjã  hžhhŸh¯h K;ubhÆ)”}”(hŒÀAssuming that we had a stable kernel source interface for the kernel, a
binary interface would naturally happen too, right?  Wrong.  Please
consider the following facts about the Linux kernel:”h]”hŒÀAssuming that we had a stable kernel source interface for the kernel, a
binary interface would naturally happen too, right?  Wrong.  Please
consider the following facts about the Linux kernel:”…””}”(hjô  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K<hjã  hžhubhŒblock_quote”“”)”}”(hX£  - Depending on the version of the C compiler you use, different kernel
  data structures will contain different alignment of structures, and
  possibly include different functions in different ways (putting
  functions inline or not.)  The individual function organization
  isn't that important, but the different data structure padding is
  very important.

- Depending on what kernel build options you select, a wide range of
  different things can be assumed by the kernel:

    - different structures can contain different fields
    - Some functions may not be implemented at all, (i.e. some locks
      compile away to nothing for non-SMP builds.)
    - Memory within the kernel can be aligned in different ways,
      depending on the build options.

- Linux runs on a wide range of different processor architectures.
  There is no way that binary drivers from one architecture will run
  on another architecture properly.
”h]”hŒbullet_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hX[  Depending on the version of the C compiler you use, different kernel
data structures will contain different alignment of structures, and
possibly include different functions in different ways (putting
functions inline or not.)  The individual function organization
isn't that important, but the different data structure padding is
very important.
”h]”hÆ)”}”(hXZ  Depending on the version of the C compiler you use, different kernel
data structures will contain different alignment of structures, and
possibly include different functions in different ways (putting
functions inline or not.)  The individual function organization
isn't that important, but the different data structure padding is
very important.”h]”hX\  Depending on the version of the C compiler you use, different kernel
data structures will contain different alignment of structures, and
possibly include different functions in different ways (putting
functions inline or not.)  The individual function organization
isnâ€™t that important, but the different data structure padding is
very important.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K@hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj
  ubj  )”}”(hX€  Depending on what kernel build options you select, a wide range of
different things can be assumed by the kernel:

  - different structures can contain different fields
  - Some functions may not be implemented at all, (i.e. some locks
    compile away to nothing for non-SMP builds.)
  - Memory within the kernel can be aligned in different ways,
    depending on the build options.
”h]”(hÆ)”}”(hŒqDepending on what kernel build options you select, a wide range of
different things can be assumed by the kernel:”h]”hŒqDepending on what kernel build options you select, a wide range of
different things can be assumed by the kernel:”…””}”(hj+  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KGhj'  ubj  )”}”(hX  - different structures can contain different fields
- Some functions may not be implemented at all, (i.e. some locks
  compile away to nothing for non-SMP builds.)
- Memory within the kernel can be aligned in different ways,
  depending on the build options.
”h]”j	  )”}”(hhh]”(j  )”}”(hŒ1different structures can contain different fields”h]”hÆ)”}”(hjB  h]”hŒ1different structures can contain different fields”…””}”(hjD  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KJhj@  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj=  ubj  )”}”(hŒkSome functions may not be implemented at all, (i.e. some locks
compile away to nothing for non-SMP builds.)”h]”hÆ)”}”(hŒkSome functions may not be implemented at all, (i.e. some locks
compile away to nothing for non-SMP builds.)”h]”hŒkSome functions may not be implemented at all, (i.e. some locks
compile away to nothing for non-SMP builds.)”…””}”(hj[  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KKhjW  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj=  ubj  )”}”(hŒ[Memory within the kernel can be aligned in different ways,
depending on the build options.
”h]”hÆ)”}”(hŒZMemory within the kernel can be aligned in different ways,
depending on the build options.”h]”hŒZMemory within the kernel can be aligned in different ways,
depending on the build options.”…””}”(hjs  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KMhjo  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj=  ubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1j  hŸh¯h KJhj9  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hŸh¯h KJhj'  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  hj
  ubj  )”}”(hŒ¦Linux runs on a wide range of different processor architectures.
There is no way that binary drivers from one architecture will run
on another architecture properly.
”h]”hÆ)”}”(hŒ¥Linux runs on a wide range of different processor architectures.
There is no way that binary drivers from one architecture will run
on another architecture properly.”h]”hŒ¥Linux runs on a wide range of different processor architectures.
There is no way that binary drivers from one architecture will run
on another architecture properly.”…””}”(hjŸ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KPhj›  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj
  ubeh}”(h]”h ]”h"]”h$]”h&]”j  jŽ  uh1j  hŸh¯h K@hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hŸh¯h K@hjã  hžhubhÆ)”}”(hX%  Now a number of these issues can be addressed by simply compiling your
module for the exact specific kernel configuration, using the same exact
C compiler that the kernel was built with.  This is sufficient if you
want to provide a module for a specific release version of a specific
Linux distribution.  But multiply that single build by the number of
different Linux distributions and the number of different supported
releases of the Linux distribution and you quickly have a nightmare of
different build options on different releases.  Also realize that each
Linux distribution release contains a number of different kernels, all
tuned to different hardware types (different processor types and
different options), so for even a single release you will need to create
multiple versions of your module.”h]”hX%  Now a number of these issues can be addressed by simply compiling your
module for the exact specific kernel configuration, using the same exact
C compiler that the kernel was built with.  This is sufficient if you
want to provide a module for a specific release version of a specific
Linux distribution.  But multiply that single build by the number of
different Linux distributions and the number of different supported
releases of the Linux distribution and you quickly have a nightmare of
different build options on different releases.  Also realize that each
Linux distribution release contains a number of different kernels, all
tuned to different hardware types (different processor types and
different options), so for even a single release you will need to create
multiple versions of your module.”…””}”(hj¿  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KThjã  hžhubhÆ)”}”(hŒTrust me, you will go insane over time if you try to support this kind
of release, I learned this the hard way a long time ago...”h]”hŒTrust me, you will go insane over time if you try to support this kind
of release, I learned this the hard way a long time ago...”…””}”(hjÍ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Kahjã  hžhubeh}”(h]”Œbinary-kernel-interface”ah ]”h"]”Œbinary kernel interface”ah$]”h&]”uh1h°hh²hžhhŸh¯h K;ubh±)”}”(hhh]”(h¶)”}”(hŒStable Kernel Source Interfaces”h]”hŒStable Kernel Source Interfaces”…””}”(hjæ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hµhjã  hžhhŸh¯h KfubhÆ)”}”(hŒšThis is a much more "volatile" topic if you talk to people who try to
keep a Linux kernel driver that is not in the main kernel tree up to
date over time.”h]”hŒžThis is a much more â€œvolatileâ€ topic if you talk to people who try to
keep a Linux kernel driver that is not in the main kernel tree up to
date over time.”…””}”(hjô  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Khhjã  hžhubhÆ)”}”(hX+  Linux kernel development is continuous and at a rapid pace, never
stopping to slow down.  As such, the kernel developers find bugs in
current interfaces, or figure out a better way to do things.  If they do
that, they then fix the current interfaces to work better.  When they do
so, function names may change, structures may grow or shrink, and
function parameters may be reworked.  If this happens, all of the
instances of where this interface is used within the kernel are fixed up
at the same time, ensuring that everything continues to work properly.”h]”hX+  Linux kernel development is continuous and at a rapid pace, never
stopping to slow down.  As such, the kernel developers find bugs in
current interfaces, or figure out a better way to do things.  If they do
that, they then fix the current interfaces to work better.  When they do
so, function names may change, structures may grow or shrink, and
function parameters may be reworked.  If this happens, all of the
instances of where this interface is used within the kernel are fixed up
at the same time, ensuring that everything continues to work properly.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Klhjã  hžhubhÆ)”}”(hŒÓAs a specific examples of this, the in-kernel USB interfaces have
undergone at least three different reworks over the lifetime of this
subsystem.  These reworks were done to address a number of different
issues:”h]”hŒÓAs a specific examples of this, the in-kernel USB interfaces have
undergone at least three different reworks over the lifetime of this
subsystem.  These reworks were done to address a number of different
issues:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Kuhjã  hžhubj  )”}”(hXá  - A change from a synchronous model of data streams to an asynchronous
  one.  This reduced the complexity of a number of drivers and
  increased the throughput of all USB drivers such that we are now
  running almost all USB devices at their maximum speed possible.
- A change was made in the way data packets were allocated from the
  USB core by USB drivers so that all drivers now needed to provide
  more information to the USB core to fix a number of documented
  deadlocks.
”h]”j	  )”}”(hhh]”(j  )”}”(hX  A change from a synchronous model of data streams to an asynchronous
one.  This reduced the complexity of a number of drivers and
increased the throughput of all USB drivers such that we are now
running almost all USB devices at their maximum speed possible.”h]”hÆ)”}”(hX  A change from a synchronous model of data streams to an asynchronous
one.  This reduced the complexity of a number of drivers and
increased the throughput of all USB drivers such that we are now
running almost all USB devices at their maximum speed possible.”h]”hX  A change from a synchronous model of data streams to an asynchronous
one.  This reduced the complexity of a number of drivers and
increased the throughput of all USB drivers such that we are now
running almost all USB devices at their maximum speed possible.”…””}”(hj)  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Kzhj%  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj"  ubj  )”}”(hŒÎA change was made in the way data packets were allocated from the
USB core by USB drivers so that all drivers now needed to provide
more information to the USB core to fix a number of documented
deadlocks.
”h]”hÆ)”}”(hŒÍA change was made in the way data packets were allocated from the
USB core by USB drivers so that all drivers now needed to provide
more information to the USB core to fix a number of documented
deadlocks.”h]”hŒÍA change was made in the way data packets were allocated from the
USB core by USB drivers so that all drivers now needed to provide
more information to the USB core to fix a number of documented
deadlocks.”…””}”(hjA  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K~hj=  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj"  ubeh}”(h]”h ]”h"]”h$]”h&]”j  jŽ  uh1j  hŸh¯h Kzhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hŸh¯h Kzhjã  hžhubhÆ)”}”(hX7  This is in stark contrast to a number of closed source operating systems
which have had to maintain their older USB interfaces over time.  This
provides the ability for new developers to accidentally use the old
interfaces and do things in improper ways, causing the stability of the
operating system to suffer.”h]”hX7  This is in stark contrast to a number of closed source operating systems
which have had to maintain their older USB interfaces over time.  This
provides the ability for new developers to accidentally use the old
interfaces and do things in improper ways, causing the stability of the
operating system to suffer.”…””}”(hja  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Kƒhjã  hžhubhÆ)”}”(hX  In both of these instances, all developers agreed that these were
important changes that needed to be made, and they were made, with
relatively little pain.  If Linux had to ensure that it will preserve a
stable source interface, a new interface would have been created, and
the older, broken one would have had to be maintained over time, leading
to extra work for the USB developers.  Since all Linux USB developers do
their work on their own time, asking programmers to do extra work for no
gain, for free, is not a possibility.”h]”hX  In both of these instances, all developers agreed that these were
important changes that needed to be made, and they were made, with
relatively little pain.  If Linux had to ensure that it will preserve a
stable source interface, a new interface would have been created, and
the older, broken one would have had to be maintained over time, leading
to extra work for the USB developers.  Since all Linux USB developers do
their work on their own time, asking programmers to do extra work for no
gain, for free, is not a possibility.”…””}”(hjo  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K‰hjã  hžhubhÆ)”}”(hX]  Security issues are also very important for Linux.  When a
security issue is found, it is fixed in a very short amount of time.  A
number of times this has caused internal kernel interfaces to be
reworked to prevent the security problem from occurring.  When this
happens, all drivers that use the interfaces were also fixed at the
same time, ensuring that the security problem was fixed and could not
come back at some future time accidentally.  If the internal interfaces
were not allowed to change, fixing this kind of security problem and
insuring that it could not happen again would not be possible.”h]”hX]  Security issues are also very important for Linux.  When a
security issue is found, it is fixed in a very short amount of time.  A
number of times this has caused internal kernel interfaces to be
reworked to prevent the security problem from occurring.  When this
happens, all drivers that use the interfaces were also fixed at the
same time, ensuring that the security problem was fixed and could not
come back at some future time accidentally.  If the internal interfaces
were not allowed to change, fixing this kind of security problem and
insuring that it could not happen again would not be possible.”…””}”(hj}  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K’hjã  hžhubhÆ)”}”(hX.  Kernel interfaces are cleaned up over time.  If there is no one using a
current interface, it is deleted.  This ensures that the kernel remains
as small as possible, and that all potential interfaces are tested as
well as they can be (unused interfaces are pretty much impossible to
test for validity.)”h]”hX.  Kernel interfaces are cleaned up over time.  If there is no one using a
current interface, it is deleted.  This ensures that the kernel remains
as small as possible, and that all potential interfaces are tested as
well as they can be (unused interfaces are pretty much impossible to
test for validity.)”…””}”(hj‹  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Kœhjã  hžhubeh}”(h]”Œstable-kernel-source-interfaces”ah ]”h"]”Œstable kernel source interfaces”ah$]”h&]”uh1h°hh²hžhhŸh¯h Kfubh±)”}”(hhh]”(h¶)”}”(hŒ
What to do”h]”hŒ
What to do”…””}”(hj¤  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hµhj¡  hžhhŸh¯h K¤ubhÆ)”}”(hX,  So, if you have a Linux kernel driver that is not in the main kernel
tree, what are you, a developer, supposed to do?  Releasing a binary
driver for every different kernel version for every distribution is a
nightmare, and trying to keep up with an ever changing kernel interface
is also a rough job.”h]”hX,  So, if you have a Linux kernel driver that is not in the main kernel
tree, what are you, a developer, supposed to do?  Releasing a binary
driver for every different kernel version for every distribution is a
nightmare, and trying to keep up with an ever changing kernel interface
is also a rough job.”…””}”(hj²  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K¦hj¡  hžhubhÆ)”}”(hXì  Simple, get your kernel driver into the main kernel tree (remember we are
talking about drivers released under a GPL-compatible license here, if your
code doesn't fall under this category, good luck, you are on your own here,
you leech).  If your driver is in the tree, and a kernel interface changes,
it will be fixed up by the person who did the kernel change in the first
place.  This ensures that your driver is always buildable, and works over
time, with very little effort on your part.”h]”hXî  Simple, get your kernel driver into the main kernel tree (remember we are
talking about drivers released under a GPL-compatible license here, if your
code doesnâ€™t fall under this category, good luck, you are on your own here,
you leech).  If your driver is in the tree, and a kernel interface changes,
it will be fixed up by the person who did the kernel change in the first
place.  This ensures that your driver is always buildable, and works over
time, with very little effort on your part.”…””}”(hjÀ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K¬hj¡  hžhubhÆ)”}”(hŒMThe very good side effects of having your driver in the main kernel tree
are:”h]”hŒMThe very good side effects of having your driver in the main kernel tree
are:”…””}”(hjÎ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K´hj¡  hžhubj  )”}”(hXã  - The quality of the driver will rise as the maintenance costs (to the
  original developer) will decrease.
- Other developers will add features to your driver.
- Other people will find and fix bugs in your driver.
- Other people will find tuning opportunities in your driver.
- Other people will update the driver for you when external interface
  changes require it.
- The driver automatically gets shipped in all Linux distributions
  without having to ask the distros to add it.
”h]”j	  )”}”(hhh]”(j  )”}”(hŒgThe quality of the driver will rise as the maintenance costs (to the
original developer) will decrease.”h]”hÆ)”}”(hŒgThe quality of the driver will rise as the maintenance costs (to the
original developer) will decrease.”h]”hŒgThe quality of the driver will rise as the maintenance costs (to the
original developer) will decrease.”…””}”(hjç  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K·hjã  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjà  ubj  )”}”(hŒ2Other developers will add features to your driver.”h]”hÆ)”}”(hjý  h]”hŒ2Other developers will add features to your driver.”…””}”(hjÿ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K¹hjû  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjà  ubj  )”}”(hŒ3Other people will find and fix bugs in your driver.”h]”hÆ)”}”(hj  h]”hŒ3Other people will find and fix bugs in your driver.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h Kºhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjà  ubj  )”}”(hŒ;Other people will find tuning opportunities in your driver.”h]”hÆ)”}”(hj+  h]”hŒ;Other people will find tuning opportunities in your driver.”…””}”(hj-  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K»hj)  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjà  ubj  )”}”(hŒWOther people will update the driver for you when external interface
changes require it.”h]”hÆ)”}”(hŒWOther people will update the driver for you when external interface
changes require it.”h]”hŒWOther people will update the driver for you when external interface
changes require it.”…””}”(hjD  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K¼hj@  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjà  ubj  )”}”(hŒnThe driver automatically gets shipped in all Linux distributions
without having to ask the distros to add it.
”h]”hÆ)”}”(hŒmThe driver automatically gets shipped in all Linux distributions
without having to ask the distros to add it.”h]”hŒmThe driver automatically gets shipped in all Linux distributions
without having to ask the distros to add it.”…””}”(hj\  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h K¾hjX  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjà  ubeh}”(h]”h ]”h"]”h$]”h&]”j  jŽ  uh1j  hŸh¯h K·hjÜ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hŸh¯h K·hj¡  hžhubhÆ)”}”(hX  As Linux supports a larger number of different devices "out of the box"
than any other operating system, and it supports these devices on more
different processor architectures than any other operating system, this
proven type of development model must be doing something right :)”h]”hX  As Linux supports a larger number of different devices â€œout of the boxâ€
than any other operating system, and it supports these devices on more
different processor architectures than any other operating system, this
proven type of development model must be doing something right :)”…””}”(hj|  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KÁhj¡  hžhubhŒ
transition”“”)”}”(hŒ------”h]”h}”(h]”h ]”h"]”h$]”h&]”uh1jŠ  hŸh¯h KÈhj¡  hžhubhÆ)”}”(hŒ¦Thanks to Randy Dunlap, Andrew Morton, David Brownell, Hanna Linder,
Robert Love, and Nishanth Aravamudan for their review and comments on
early drafts of this paper.”h]”hŒ¦Thanks to Randy Dunlap, Andrew Morton, David Brownell, Hanna Linder,
Robert Love, and Nishanth Aravamudan for their review and comments on
early drafts of this paper.”…””}”(hj–  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhŸh¯h KÊhj¡  hžhubeh}”(h]”Œ
what-to-do”ah ]”h"]”Œ
what to do”ah$]”h&]”uh1h°hh²hžhhŸh¯h K¤ubeh}”(h]”(Œ!the-linux-kernel-driver-interface”h®eh ]”h"]”(Œ!the linux kernel driver interface”Œstable_api_nonsense”eh$]”h&]”uh1h°hhhžhhŸh¯h KŒexpect_referenced_by_name”}”j²  h£sŒexpect_referenced_by_id”}”h®h£subeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h¯uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(hµNŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”jÜ  Œerror_encoding”Œutf-8”Œerror_encoding_error_handler”Œbackslashreplace”Œlanguage_code”Œen”Œrecord_dependencies”NŒconfig”NŒ	id_prefix”hŒauto_id_prefix”Œid”Œdump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”h¯Œ_destination”NŒ_config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒfile_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œpep_references”NŒpep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒrfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ	tab_width”KŒtrim_footnote_reference_space”‰Œsyntax_highlight”Œlong”Œsmart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œdocinfo_xform”KŒsectsubtitle_xform”‰Œimage_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”h®]”h£asŒnameids”}”(j²  h®j±  j®  j‹  jˆ  jà  jÝ  jà  jÝ  jž  j›  j©  j¦  uŒ	nametypes”}”(j²  ˆj±  ‰j‹  ‰jà  ‰jà  ‰jž  ‰j©  ‰uh}”(h®h²j®  h²jˆ  jg  jÝ  jŽ  jÝ  jã  j›  jã  j¦  j¡  uŒfootnote_refs”}”Œcitation_refs”}”Œautofootnotes”]”Œautofootnote_refs”]”Œsymbol_footnotes”]”Œsymbol_footnote_refs”]”Œ	footnotes”]”Œ	citations”]”Œautofootnote_start”KŒsymbol_footnote_start”K Œ
id_counter”Œcollections”ŒCounter”“”}”…”R”Œparse_messages”]”Œtransform_messages”]”hŒsystem_message”“”)”}”(hhh]”hÆ)”}”(hhh]”hŒ9Hyperlink target "stable-api-nonsense" is not referenced.”…””}”hjF  sbah}”(h]”h ]”h"]”h$]”h&]”uh1hÅhjC  ubah}”(h]”h ]”h"]”h$]”h&]”Œlevel”KŒtype”ŒINFO”Œsource”h¯Œline”Kuh1jA  ubaŒtransformer”NŒinclude_log”]”Œ
decoration”Nhžhub.