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Commit 12983bcd authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab
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Documentation/adding-syscalls.txt: convert it to ReST markup 

Convert adding-syscalls.txt to ReST markup and add it to the
development-process book:

- add extra lines to make Sphinx to correctly parse paragraphs;
- use quote blocks for examples;
- use monotonic font for dirs, function calls, etc;
- mark manpage pages using the right markup;
- add cross-reference to SubmittingPatches.
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
parent 3a61badd
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Documentation/adding-syscalls.txt → Documentation/adding-syscals.txt
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......@@ -3,7 +3,7 @@ Adding a New System Call
This document describes what's involved in adding a new system call to the
Linux kernel, over and above the normal submission advice in
Documentation/SubmittingPatches.
:ref:`Documentation/SubmittingPatches <submittingpatches>`.
System Call Alternatives
......@@ -19,30 +19,33 @@ interface.
object, it may make more sense to create a new filesystem or device. This
also makes it easier to encapsulate the new functionality in a kernel module
rather than requiring it to be built into the main kernel.
- If the new functionality involves operations where the kernel notifies
userspace that something has happened, then returning a new file
descriptor for the relevant object allows userspace to use
poll/select/epoll to receive that notification.
- However, operations that don't map to read(2)/write(2)-like operations
have to be implemented as ioctl(2) requests, which can lead to a
somewhat opaque API.
``poll``/``select``/``epoll`` to receive that notification.
- However, operations that don't map to
:manpage:`read(2)`/:manpage:`write(2)`-like operations
have to be implemented as :manpage:`ioctl(2)` requests, which can lead
to a somewhat opaque API.
- If you're just exposing runtime system information, a new node in sysfs
(see Documentation/filesystems/sysfs.txt) or the /proc filesystem may be
more appropriate. However, access to these mechanisms requires that the
(see ``Documentation/filesystems/sysfs.txt``) or the ``/proc`` filesystem may
be more appropriate. However, access to these mechanisms requires that the
relevant filesystem is mounted, which might not always be the case (e.g.
in a namespaced/sandboxed/chrooted environment). Avoid adding any API to
debugfs, as this is not considered a 'production' interface to userspace.
- If the operation is specific to a particular file or file descriptor, then
an additional fcntl(2) command option may be more appropriate. However,
fcntl(2) is a multiplexing system call that hides a lot of complexity, so
an additional :manpage:`fcntl(2)` command option may be more appropriate. However,
:manpage:`fcntl(2)` is a multiplexing system call that hides a lot of complexity, so
this option is best for when the new function is closely analogous to
existing fcntl(2) functionality, or the new functionality is very simple
existing :manpage:`fcntl(2)` functionality, or the new functionality is very simple
(for example, getting/setting a simple flag related to a file descriptor).
- If the operation is specific to a particular task or process, then an
additional prctl(2) command option may be more appropriate. As with
fcntl(2), this system call is a complicated multiplexor so is best reserved
for near-analogs of existing prctl() commands or getting/setting a simple
flag related to a process.
additional :manpage:`prctl(2)` command option may be more appropriate. As
with :manpage:`fcntl(2)`, this system call is a complicated multiplexor so
is best reserved for near-analogs of existing ``prctl()`` commands or
getting/setting a simple flag related to a process.
Designing the API: Planning for Extension
......@@ -54,15 +57,16 @@ interface on the kernel mailing list, and it's important to plan for future
extensions of the interface.
(The syscall table is littered with historical examples where this wasn't done,
together with the corresponding follow-up system calls -- eventfd/eventfd2,
dup2/dup3, inotify_init/inotify_init1, pipe/pipe2, renameat/renameat2 -- so
together with the corresponding follow-up system calls --
``eventfd``/``eventfd2``, ``dup2``/``dup3``, ``inotify_init``/``inotify_init1``,
``pipe``/``pipe2``, ``renameat``/``renameat2`` -- so
learn from the history of the kernel and plan for extensions from the start.)
For simpler system calls that only take a couple of arguments, the preferred
way to allow for future extensibility is to include a flags argument to the
system call. To make sure that userspace programs can safely use flags
between kernel versions, check whether the flags value holds any unknown
flags, and reject the system call (with EINVAL) if it does:
flags, and reject the system call (with ``EINVAL``) if it does::
if (flags & ~(THING_FLAG1 | THING_FLAG2 | THING_FLAG3))
return -EINVAL;
......@@ -72,7 +76,7 @@ flags, and reject the system call (with EINVAL) if it does:
For more sophisticated system calls that involve a larger number of arguments,
it's preferred to encapsulate the majority of the arguments into a structure
that is passed in by pointer. Such a structure can cope with future extension
by including a size argument in the structure:
by including a size argument in the structure::
struct xyzzy_params {
u32 size; /* userspace sets p->size = sizeof(struct xyzzy_params) */
......@@ -81,19 +85,19 @@ by including a size argument in the structure:
u64 param_3;
};
As long as any subsequently added field, say param_4, is designed so that a
As long as any subsequently added field, say ``param_4``, is designed so that a
zero value gives the previous behaviour, then this allows both directions of
version mismatch:
- To cope with a later userspace program calling an older kernel, the kernel
code should check that any memory beyond the size of the structure that it
expects is zero (effectively checking that param_4 == 0).
expects is zero (effectively checking that ``param_4 == 0``).
- To cope with an older userspace program calling a newer kernel, the kernel
code can zero-extend a smaller instance of the structure (effectively
setting param_4 = 0).
setting ``param_4 = 0``).
See perf_event_open(2) and the perf_copy_attr() function (in
kernel/events/core.c) for an example of this approach.
See :manpage:`perf_event_open(2)` and the ``perf_copy_attr()`` function (in
``kernel/events/core.c``) for an example of this approach.
Designing the API: Other Considerations
......@@ -104,57 +108,60 @@ should use a file descriptor as the handle for that object -- don't invent a
new type of userspace object handle when the kernel already has mechanisms and
well-defined semantics for using file descriptors.
If your new xyzzy(2) system call does return a new file descriptor, then the
flags argument should include a value that is equivalent to setting O_CLOEXEC
on the new FD. This makes it possible for userspace to close the timing
window between xyzzy() and calling fcntl(fd, F_SETFD, FD_CLOEXEC), where an
unexpected fork() and execve() in another thread could leak a descriptor to
If your new :manpage:`xyzzy(2)` system call does return a new file descriptor,
then the flags argument should include a value that is equivalent to setting
``O_CLOEXEC`` on the new FD. This makes it possible for userspace to close
the timing window between ``xyzzy()`` and calling
``fcntl(fd, F_SETFD, FD_CLOEXEC)``, where an unexpected ``fork()`` and
``execve()`` in another thread could leak a descriptor to
the exec'ed program. (However, resist the temptation to re-use the actual value
of the O_CLOEXEC constant, as it is architecture-specific and is part of a
numbering space of O_* flags that is fairly full.)
of the ``O_CLOEXEC`` constant, as it is architecture-specific and is part of a
numbering space of ``O_*`` flags that is fairly full.)
If your system call returns a new file descriptor, you should also consider
what it means to use the poll(2) family of system calls on that file
what it means to use the :manpage:`poll(2)` family of system calls on that file
descriptor. Making a file descriptor ready for reading or writing is the
normal way for the kernel to indicate to userspace that an event has
occurred on the corresponding kernel object.
If your new xyzzy(2) system call involves a filename argument:
If your new :manpage:`xyzzy(2)` system call involves a filename argument::
int sys_xyzzy(const char __user *path, ..., unsigned int flags);
you should also consider whether an xyzzyat(2) version is more appropriate:
you should also consider whether an :manpage:`xyzzyat(2)` version is more appropriate::
int sys_xyzzyat(int dfd, const char __user *path, ..., unsigned int flags);
This allows more flexibility for how userspace specifies the file in question;
in particular it allows userspace to request the functionality for an
already-opened file descriptor using the AT_EMPTY_PATH flag, effectively giving
an fxyzzy(3) operation for free:
already-opened file descriptor using the ``AT_EMPTY_PATH`` flag, effectively
giving an :manpage:`fxyzzy(3)` operation for free::
- xyzzyat(AT_FDCWD, path, ..., 0) is equivalent to xyzzy(path,...)
- xyzzyat(fd, "", ..., AT_EMPTY_PATH) is equivalent to fxyzzy(fd, ...)
(For more details on the rationale of the *at() calls, see the openat(2) man
page; for an example of AT_EMPTY_PATH, see the fstatat(2) man page.)
If your new xyzzy(2) system call involves a parameter describing an offset
within a file, make its type loff_t so that 64-bit offsets can be supported
even on 32-bit architectures.
If your new xyzzy(2) system call involves privileged functionality, it needs
to be governed by the appropriate Linux capability bit (checked with a call to
capable()), as described in the capabilities(7) man page. Choose an existing
capability bit that governs related functionality, but try to avoid combining
lots of only vaguely related functions together under the same bit, as this
goes against capabilities' purpose of splitting the power of root. In
particular, avoid adding new uses of the already overly-general CAP_SYS_ADMIN
capability.
If your new xyzzy(2) system call manipulates a process other than the calling
process, it should be restricted (using a call to ptrace_may_access()) so that
only a calling process with the same permissions as the target process, or
with the necessary capabilities, can manipulate the target process.
(For more details on the rationale of the \*at() calls, see the
:manpage:`openat(2)` man page; for an example of AT_EMPTY_PATH, see the
:manpage:`fstatat(2)` man page.)
If your new :manpage:`xyzzy(2)` system call involves a parameter describing an
offset within a file, make its type ``loff_t`` so that 64-bit offsets can be
supported even on 32-bit architectures.
If your new :manpage:`xyzzy(2)` system call involves privileged functionality,
it needs to be governed by the appropriate Linux capability bit (checked with
a call to ``capable()``), as described in the :manpage:`capabilities(7)` man
page. Choose an existing capability bit that governs related functionality,
but try to avoid combining lots of only vaguely related functions together
under the same bit, as this goes against capabilities' purpose of splitting
the power of root. In particular, avoid adding new uses of the already
overly-general ``CAP_SYS_ADMIN`` capability.
If your new :manpage:`xyzzy(2)` system call manipulates a process other than
the calling process, it should be restricted (using a call to
``ptrace_may_access()``) so that only a calling process with the same
permissions as the target process, or with the necessary capabilities, can
manipulate the target process.
Finally, be aware that some non-x86 architectures have an easier time if
system call parameters that are explicitly 64-bit fall on odd-numbered
......@@ -175,7 +182,7 @@ distinct commits (each of which is described further below):
- Wiring up of the new system call for one particular architecture, usually
x86 (including all of x86_64, x86_32 and x32).
- A demonstration of the use of the new system call in userspace via a
selftest in tools/testing/selftests/.
selftest in ``tools/testing/selftests/``.
- A draft man-page for the new system call, either as plain text in the
cover letter, or as a patch to the (separate) man-pages repository.
......@@ -186,24 +193,24 @@ be cc'ed to linux-api@vger.kernel.org.
Generic System Call Implementation
----------------------------------
The main entry point for your new xyzzy(2) system call will be called
sys_xyzzy(), but you add this entry point with the appropriate
SYSCALL_DEFINEn() macro rather than explicitly. The 'n' indicates the number
of arguments to the system call, and the macro takes the system call name
The main entry point for your new :manpage:`xyzzy(2)` system call will be called
``sys_xyzzy()``, but you add this entry point with the appropriate
``SYSCALL_DEFINEn()`` macro rather than explicitly. The 'n' indicates the
number of arguments to the system call, and the macro takes the system call name
followed by the (type, name) pairs for the parameters as arguments. Using
this macro allows metadata about the new system call to be made available for
other tools.
The new entry point also needs a corresponding function prototype, in
include/linux/syscalls.h, marked as asmlinkage to match the way that system
calls are invoked:
``include/linux/syscalls.h``, marked as asmlinkage to match the way that system
calls are invoked::
asmlinkage long sys_xyzzy(...);
Some architectures (e.g. x86) have their own architecture-specific syscall
tables, but several other architectures share a generic syscall table. Add your
new system call to the generic list by adding an entry to the list in
include/uapi/asm-generic/unistd.h:
``include/uapi/asm-generic/unistd.h``::
#define __NR_xyzzy 292
__SYSCALL(__NR_xyzzy, sys_xyzzy)
......@@ -212,30 +219,30 @@ Also update the __NR_syscalls count to reflect the additional system call, and
note that if multiple new system calls are added in the same merge window,
your new syscall number may get adjusted to resolve conflicts.
The file kernel/sys_ni.c provides a fallback stub implementation of each system
call, returning -ENOSYS. Add your new system call here too:
The file ``kernel/sys_ni.c`` provides a fallback stub implementation of each
system call, returning ``-ENOSYS``. Add your new system call here too::
cond_syscall(sys_xyzzy);
Your new kernel functionality, and the system call that controls it, should
normally be optional, so add a CONFIG option (typically to init/Kconfig) for
it. As usual for new CONFIG options:
normally be optional, so add a ``CONFIG`` option (typically to
``init/Kconfig``) for it. As usual for new ``CONFIG`` options:
- Include a description of the new functionality and system call controlled
by the option.
- Make the option depend on EXPERT if it should be hidden from normal users.
- Make any new source files implementing the function dependent on the CONFIG
option in the Makefile (e.g. "obj-$(CONFIG_XYZZY_SYSCALL) += xyzzy.c").
option in the Makefile (e.g. ``obj-$(CONFIG_XYZZY_SYSCALL) += xyzzy.c``).
- Double check that the kernel still builds with the new CONFIG option turned
off.
To summarize, you need a commit that includes:
- CONFIG option for the new function, normally in init/Kconfig
- SYSCALL_DEFINEn(xyzzy, ...) for the entry point
- corresponding prototype in include/linux/syscalls.h
- generic table entry in include/uapi/asm-generic/unistd.h
- fallback stub in kernel/sys_ni.c
- ``CONFIG`` option for the new function, normally in ``init/Kconfig``
- ``SYSCALL_DEFINEn(xyzzy, ...)`` for the entry point
- corresponding prototype in ``include/linux/syscalls.h``
- generic table entry in ``include/uapi/asm-generic/unistd.h``
- fallback stub in ``kernel/sys_ni.c``
x86 System Call Implementation
......@@ -244,11 +251,11 @@ x86 System Call Implementation
To wire up your new system call for x86 platforms, you need to update the
master syscall tables. Assuming your new system call isn't special in some
way (see below), this involves a "common" entry (for x86_64 and x32) in
arch/x86/entry/syscalls/syscall_64.tbl:
arch/x86/entry/syscalls/syscall_64.tbl::
333 common xyzzy sys_xyzzy
and an "i386" entry in arch/x86/entry/syscalls/syscall_32.tbl:
and an "i386" entry in ``arch/x86/entry/syscalls/syscall_32.tbl``::
380 i386 xyzzy sys_xyzzy
......@@ -267,48 +274,49 @@ However, there are a couple of situations where a compatibility layer is
needed to cope with size differences between 32-bit and 64-bit.
The first is if the 64-bit kernel also supports 32-bit userspace programs, and
so needs to parse areas of (__user) memory that could hold either 32-bit or
so needs to parse areas of (``__user``) memory that could hold either 32-bit or
64-bit values. In particular, this is needed whenever a system call argument
is:
- a pointer to a pointer
- a pointer to a struct containing a pointer (e.g. struct iovec __user *)
- a pointer to a varying sized integral type (time_t, off_t, long, ...)
- a pointer to a struct containing a pointer (e.g. ``struct iovec __user *``)
- a pointer to a varying sized integral type (``time_t``, ``off_t``,
``long``, ...)
- a pointer to a struct containing a varying sized integral type.
The second situation that requires a compatibility layer is if one of the
system call's arguments has a type that is explicitly 64-bit even on a 32-bit
architecture, for example loff_t or __u64. In this case, a value that arrives
at a 64-bit kernel from a 32-bit application will be split into two 32-bit
values, which then need to be re-assembled in the compatibility layer.
architecture, for example ``loff_t`` or ``__u64``. In this case, a value that
arrives at a 64-bit kernel from a 32-bit application will be split into two
32-bit values, which then need to be re-assembled in the compatibility layer.
(Note that a system call argument that's a pointer to an explicit 64-bit type
does *not* need a compatibility layer; for example, splice(2)'s arguments of
type loff_t __user * do not trigger the need for a compat_ system call.)
does **not** need a compatibility layer; for example, :manpage:`splice(2)`'s arguments of
type ``loff_t __user *`` do not trigger the need for a ``compat_`` system call.)
The compatibility version of the system call is called compat_sys_xyzzy(), and
is added with the COMPAT_SYSCALL_DEFINEn() macro, analogously to
The compatibility version of the system call is called ``compat_sys_xyzzy()``,
and is added with the ``COMPAT_SYSCALL_DEFINEn()`` macro, analogously to
SYSCALL_DEFINEn. This version of the implementation runs as part of a 64-bit
kernel, but expects to receive 32-bit parameter values and does whatever is
needed to deal with them. (Typically, the compat_sys_ version converts the
values to 64-bit versions and either calls on to the sys_ version, or both of
needed to deal with them. (Typically, the ``compat_sys_`` version converts the
values to 64-bit versions and either calls on to the ``sys_`` version, or both of
them call a common inner implementation function.)
The compat entry point also needs a corresponding function prototype, in
include/linux/compat.h, marked as asmlinkage to match the way that system
calls are invoked:
``include/linux/compat.h``, marked as asmlinkage to match the way that system
calls are invoked::
asmlinkage long compat_sys_xyzzy(...);
If the system call involves a structure that is laid out differently on 32-bit
and 64-bit systems, say struct xyzzy_args, then the include/linux/compat.h
header file should also include a compat version of the structure (struct
compat_xyzzy_args) where each variable-size field has the appropriate compat_
type that corresponds to the type in struct xyzzy_args. The
compat_sys_xyzzy() routine can then use this compat_ structure to parse the
arguments from a 32-bit invocation.
and 64-bit systems, say ``struct xyzzy_args``, then the include/linux/compat.h
header file should also include a compat version of the structure (``struct
compat_xyzzy_args``) where each variable-size field has the appropriate
``compat_`` type that corresponds to the type in ``struct xyzzy_args``. The
``compat_sys_xyzzy()`` routine can then use this ``compat_`` structure to
parse the arguments from a 32-bit invocation.
For example, if there are fields:
For example, if there are fields::
struct xyzzy_args {
const char __user *ptr;
......@@ -317,7 +325,7 @@ For example, if there are fields:
/* ... */
};
in struct xyzzy_args, then struct compat_xyzzy_args would have:
in struct xyzzy_args, then struct compat_xyzzy_args would have::
struct compat_xyzzy_args {
compat_uptr_t ptr;
......@@ -327,18 +335,19 @@ in struct xyzzy_args, then struct compat_xyzzy_args would have:
};
The generic system call list also needs adjusting to allow for the compat
version; the entry in include/uapi/asm-generic/unistd.h should use
__SC_COMP rather than __SYSCALL:
version; the entry in ``include/uapi/asm-generic/unistd.h`` should use
``__SC_COMP`` rather than ``__SYSCALL``::
#define __NR_xyzzy 292
__SC_COMP(__NR_xyzzy, sys_xyzzy, compat_sys_xyzzy)
To summarize, you need:
- a COMPAT_SYSCALL_DEFINEn(xyzzy, ...) for the compat entry point
- corresponding prototype in include/linux/compat.h
- (if needed) 32-bit mapping struct in include/linux/compat.h
- instance of __SC_COMP not __SYSCALL in include/uapi/asm-generic/unistd.h
- a ``COMPAT_SYSCALL_DEFINEn(xyzzy, ...)`` for the compat entry point
- corresponding prototype in ``include/linux/compat.h``
- (if needed) 32-bit mapping struct in ``include/linux/compat.h``
- instance of ``__SC_COMP`` not ``__SYSCALL`` in
``include/uapi/asm-generic/unistd.h``
Compatibility System Calls (x86)
......@@ -347,9 +356,9 @@ Compatibility System Calls (x86)
To wire up the x86 architecture of a system call with a compatibility version,
the entries in the syscall tables need to be adjusted.
First, the entry in arch/x86/entry/syscalls/syscall_32.tbl gets an extra
First, the entry in ``arch/x86/entry/syscalls/syscall_32.tbl`` gets an extra
column to indicate that a 32-bit userspace program running on a 64-bit kernel
should hit the compat entry point:
should hit the compat entry point::
380 i386 xyzzy sys_xyzzy compat_sys_xyzzy
......@@ -359,8 +368,8 @@ should either match the 64-bit version or the 32-bit version.
If there's a pointer-to-a-pointer involved, the decision is easy: x32 is
ILP32, so the layout should match the 32-bit version, and the entry in
arch/x86/entry/syscalls/syscall_64.tbl is split so that x32 programs hit the
compatibility wrapper:
``arch/x86/entry/syscalls/syscall_64.tbl`` is split so that x32 programs hit
the compatibility wrapper::
333 64 xyzzy sys_xyzzy
...
......@@ -384,8 +393,9 @@ stack the same and most of the registers the same as before the system call,
and with the same virtual memory space.
However, a few system calls do things differently. They might return to a
different location (rt_sigreturn) or change the memory space (fork/vfork/clone)
or even architecture (execve/execveat) of the program.
different location (``rt_sigreturn``) or change the memory space
(``fork``/``vfork``/``clone``) or even architecture (``execve``/``execveat``)
of the program.
To allow for this, the kernel implementation of the system call may need to
save and restore additional registers to the kernel stack, allowing complete
......@@ -395,31 +405,31 @@ This is arch-specific, but typically involves defining assembly entry points
that save/restore additional registers and invoke the real system call entry
point.
For x86_64, this is implemented as a stub_xyzzy entry point in
arch/x86/entry/entry_64.S, and the entry in the syscall table
(arch/x86/entry/syscalls/syscall_64.tbl) is adjusted to match:
For x86_64, this is implemented as a ``stub_xyzzy`` entry point in
``arch/x86/entry/entry_64.S``, and the entry in the syscall table
(``arch/x86/entry/syscalls/syscall_64.tbl``) is adjusted to match::
333 common xyzzy stub_xyzzy
The equivalent for 32-bit programs running on a 64-bit kernel is normally
called stub32_xyzzy and implemented in arch/x86/entry/entry_64_compat.S,
called ``stub32_xyzzy`` and implemented in ``arch/x86/entry/entry_64_compat.S``,
with the corresponding syscall table adjustment in
arch/x86/entry/syscalls/syscall_32.tbl:
``arch/x86/entry/syscalls/syscall_32.tbl``::
380 i386 xyzzy sys_xyzzy stub32_xyzzy
If the system call needs a compatibility layer (as in the previous section)
then the stub32_ version needs to call on to the compat_sys_ version of the
system call rather than the native 64-bit version. Also, if the x32 ABI
then the ``stub32_`` version needs to call on to the ``compat_sys_`` version
of the system call rather than the native 64-bit version. Also, if the x32 ABI
implementation is not common with the x86_64 version, then its syscall
table will also need to invoke a stub that calls on to the compat_sys_
table will also need to invoke a stub that calls on to the ``compat_sys_``
version.
For completeness, it's also nice to set up a mapping so that user-mode Linux
still works -- its syscall table will reference stub_xyzzy, but the UML build
doesn't include arch/x86/entry/entry_64.S implementation (because UML
doesn't include ``arch/x86/entry/entry_64.S`` implementation (because UML
simulates registers etc). Fixing this is as simple as adding a #define to
arch/x86/um/sys_call_table_64.c:
``arch/x86/um/sys_call_table_64.c``::
#define stub_xyzzy sys_xyzzy
......@@ -432,9 +442,9 @@ occasional exception that may need updating for your particular system call.
The audit subsystem is one such special case; it includes (arch-specific)
functions that classify some special types of system call -- specifically
file open (open/openat), program execution (execve/exeveat) or socket
multiplexor (socketcall) operations. If your new system call is analogous to
one of these, then the audit system should be updated.
file open (``open``/``openat``), program execution (``execve``/``exeveat``) or
socket multiplexor (``socketcall``) operations. If your new system call is
analogous to one of these, then the audit system should be updated.
More generally, if there is an existing system call that is analogous to your
new system call, it's worth doing a kernel-wide grep for the existing system
......@@ -447,10 +457,10 @@ Testing
A new system call should obviously be tested; it is also useful to provide
reviewers with a demonstration of how user space programs will use the system
call. A good way to combine these aims is to include a simple self-test
program in a new directory under tools/testing/selftests/.
program in a new directory under ``tools/testing/selftests/``.
For a new system call, there will obviously be no libc wrapper function and so
the test will need to invoke it using syscall(); also, if the system call
the test will need to invoke it using ``syscall()``; also, if the system call
involves a new userspace-visible structure, the corresponding header will need
to be installed to compile the test.
......@@ -461,6 +471,7 @@ and x32 (-mx32) ABI program.
For more extensive and thorough testing of new functionality, you should also
consider adding tests to the Linux Test Project, or to the xfstests project
for filesystem-related changes.
- https://linux-test-project.github.io/
- git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git
......@@ -487,12 +498,14 @@ References and Sources
arguments: https://lwn.net/Articles/311630/
- Pair of LWN articles from David Drysdale that describe the system call
implementation paths in detail for v3.14:
- https://lwn.net/Articles/604287/
- https://lwn.net/Articles/604515/
- Architecture-specific requirements for system calls are discussed in the
syscall(2) man-page:
:manpage:`syscall(2)` man-page:
http://man7.org/linux/man-pages/man2/syscall.2.html#NOTES
- Collated emails from Linus Torvalds discussing the problems with ioctl():
- Collated emails from Linus Torvalds discussing the problems with ``ioctl()``:
http://yarchive.net/comp/linux/ioctl.html
- "How to not invent kernel interfaces", Arnd Bergmann,
http://www.ukuug.org/events/linux2007/2007/papers/Bergmann.pdf
......@@ -507,17 +520,19 @@ References and Sources
commit: https://lkml.org/lkml/2014/11/19/254
- Suggestion from Greg Kroah-Hartman that it's good for new system calls to
come with a man-page & selftest: https://lkml.org/lkml/2014/3/19/710
- Discussion from Michael Kerrisk of new system call vs. prctl(2) extension:
- Discussion from Michael Kerrisk of new system call vs. :manpage:`prctl(2)` extension:
https://lkml.org/lkml/2014/6/3/411
- Suggestion from Ingo Molnar that system calls that involve multiple
arguments should encapsulate those arguments in a struct, which includes a
size field for future extensibility: https://lkml.org/lkml/2015/7/30/117
- Numbering oddities arising from (re-)use of O_* numbering space flags:
- commit 75069f2b5bfb ("vfs: renumber FMODE_NONOTIFY and add to uniqueness
check")
- commit 12ed2e36c98a ("fanotify: FMODE_NONOTIFY and __O_SYNC in sparc
conflict")
- commit bb458c644a59 ("Safer ABI for O_TMPFILE")
- Discussion from Matthew Wilcox about restrictions on 64-bit arguments:
https://lkml.org/lkml/2008/12/12/187
- Recommendation from Greg Kroah-Hartman that unknown flags should be
......
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