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include/linux/syscalls.h

Syscall function prototypes

include/linux/syscalls.h contains, among others, the function prototypes for syscalls. 
#ifndef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
asmlinkage long sys_io_setup(unsigned nr_reqs, aio_context_t __user *ctx);
asmlinkage long sys_io_destroy(aio_context_t ctx);
asmlinkage long sys_io_submit(aio_context_t, long, struct iocb __user * __user *);
asmlinkage long sys_io_cancel(aio_context_t ctx_id, struct iocb __user *iocb, struct io_event __user *result);
…
#endif

Macros

Some macros that are used in conjuction with sys calls include

See also

include/uapi/asm-generic/unistd.h defines the syscall function numbers (__NR_…)
arch/x86/include/asm/syscall.h

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