Date: Sun, 29 Oct 2017 14:50:21 +0100 From: Polytropon <freebsd@edvax.de> To: =?UTF-8?B?6aKc5Z+65bG5?= <aynuxsakura@gmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: FreeBSD Kernel Question Message-ID: <20171029145021.00d5e829.freebsd@edvax.de> In-Reply-To: <CAJFY08yVZv7b7TqXp9qELCjmqfBJO-jf_KZ-cqgOEVnJLTbROg@mail.gmail.com> References: <CAJFY08yVZv7b7TqXp9qELCjmqfBJO-jf_KZ-cqgOEVnJLTbROg@mail.gmail.com>
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On Sun, 29 Oct 2017 17:03:34 +0800, 颜基屹 wrote: > Hello! I would like to know how to provide an API in the kernel space to > user space.Such As 'printf'. To be precise, printf() isn't a kernel interface, it's a library function (of the system's C library). The kernel equivalent would probably be the system call write(). See "man 2 write" and "man 3 printf" for details. If you want to add a mechanism that deals with kernel structures and functions from user space, I'd suggest having a look at the source code of the system C library. You can implement you own API in a similar way. But you can also add a new system call; extend the system call table and add your own code to the kernel. The kernel source is a good place to learn how to do this. -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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