Lines Matching refs:system
4 This document describes what's involved in adding a new system call to the
12 The first thing to consider when adding a new system call is whether one of
13 the alternatives might be suitable instead. Although system calls are the
29 - If you're just exposing runtime system information, a new node in sysfs
37 fcntl(2) is a multiplexing system call that hides a lot of complexity, so
43 fcntl(2), this system call is a complicated multiplexor so is best reserved
51 A new system call forms part of the API of the kernel, and has to be supported
57 together with the corresponding follow-up system calls -- eventfd/eventfd2,
61 For simpler system calls that only take a couple of arguments, the preferred
63 system call. To make sure that userspace programs can safely use flags
65 flags, and reject the system call (with EINVAL) if it does:
72 For more sophisticated system calls that involve a larger number of arguments,
102 If your new system call allows userspace to refer to a kernel object, it
107 If your new xyzzy(2) system call does return a new file descriptor, then the
116 If your system call returns a new file descriptor, you should also consider
117 what it means to use the poll(2) family of system calls on that file
122 If your new xyzzy(2) system call involves a filename argument:
141 If your new xyzzy(2) system call involves a parameter describing an offset
145 If your new xyzzy(2) system call involves privileged functionality, it needs
154 If your new xyzzy(2) system call manipulates a process other than the calling
160 system call parameters that are explicitly 64-bit fall on odd-numbered
169 To make new system calls easy to review, it's best to divide up the patchset
173 - The core implementation of the system call, together with prototypes,
175 - Wiring up of the new system call for one particular architecture, usually
177 - A demonstration of the use of the new system call in userspace via a
179 - A draft man-page for the new system call, either as plain text in the
182 New system call proposals, like any change to the kernel's API, should always
189 The main entry point for your new xyzzy(2) system call will be called
192 of arguments to the system call, and the macro takes the system call name
194 this macro allows metadata about the new system call to be made available for
198 include/linux/syscalls.h, marked as asmlinkage to match the way that system
205 new system call to the generic list by adding an entry to the list in
211 Also update the __NR_syscalls count to reflect the additional system call, and
212 note that if multiple new system calls are added in the same merge window,
215 The file kernel/sys_ni.c provides a fallback stub implementation of each system
216 call, returning -ENOSYS. Add your new system call here too:
220 Your new kernel functionality, and the system call that controls it, should
224 - Include a description of the new functionality and system call controlled
244 To wire up your new system call for x86 platforms, you need to update the
245 master syscall tables. Assuming your new system call isn't special in some
262 For most system calls the same 64-bit implementation can be invoked even when
263 the userspace program is itself 32-bit; even if the system call's parameters
271 64-bit values. In particular, this is needed whenever a system call argument
280 system call's arguments has a type that is explicitly 64-bit even on a 32-bit
285 (Note that a system call argument that's a pointer to an explicit 64-bit type
287 type loff_t __user * do not trigger the need for a compat_ system call.)
289 The compatibility version of the system call is called compat_sys_xyzzy(), and
298 include/linux/compat.h, marked as asmlinkage to match the way that system
303 If the system call involves a structure that is laid out differently on 32-bit
329 The generic system call list also needs adjusting to allow for the compat
347 To wire up the x86 architecture of a system call with a compatibility version,
357 the new system call. There's a choice here: the layout of the arguments
369 If no pointers are involved, then it is preferable to re-use the 64-bit system
381 For most system calls, once the system call is complete the user program
383 stack the same and most of the registers the same as before the system call,
386 However, a few system calls do things differently. They might return to a
390 To allow for this, the kernel implementation of the system call may need to
392 control of where and how execution continues after the system call.
395 that save/restore additional registers and invoke the real system call entry
411 If the system call needs a compatibility layer (as in the previous section)
413 system call rather than the native 64-bit version. Also, if the x32 ABI
430 Most of the kernel treats system calls in a generic way, but there is the
431 occasional exception that may need updating for your particular system call.
434 functions that classify some special types of system call -- specifically
436 multiplexor (socketcall) operations. If your new system call is analogous to
437 one of these, then the audit system should be updated.
439 More generally, if there is an existing system call that is analogous to your
440 new system call, it's worth doing a kernel-wide grep for the existing system
447 A new system call should obviously be tested; it is also useful to provide
448 reviewers with a demonstration of how user space programs will use the system
452 For a new system call, there will obviously be no libc wrapper function and so
453 the test will need to invoke it using syscall(); also, if the system call
471 All new system calls should come with a complete man page, ideally using groff
482 - LWN article from Michael Kerrisk on use of flags argument in system calls:
484 - LWN article from Michael Kerrisk on how to handle unknown flags in a system
486 - LWN article from Jake Edge describing constraints on 64-bit system call
488 - Pair of LWN articles from David Drysdale that describe the system call
492 - Architecture-specific requirements for system calls are discussed in the
502 system call should come in the same email thread:
504 - Recommendation from Michael Kerrisk that a new system call should come with
508 - Suggestion from Greg Kroah-Hartman that it's good for new system calls to
510 - Discussion from Michael Kerrisk of new system call vs. prctl(2) extension:
512 - Suggestion from Ingo Molnar that system calls that involve multiple
525 - Recommendation from Linus Torvalds that x32 system calls should prefer