Good Night,<\/p>\n
First of all, what is VFS? VFS means Virtual File System. It is a layer that exists in a lot of OS and in Minix too, this layer takes care of the communication with the File System. It is a Master’s thesis in Computer Science from Bal\u00e1zs Ger\u00f3fi and the name is “Design and implementation of the MINIX Virtual File system<\/a>“. <\/p>\n <\/p>\n But why to communicate with VFS server? Or why to add something on it? If you want to some tasks you need to do a SYSCALL to it. But sometimes the VFS server don’t do what you want. So you must add and change it to do it. <\/p>\n How to do this?<\/p>\n Edit “\/usr\/src\/include\/minix\/callnr.h”. After this line “#define GETPGRP\t\t 63″ add this: Then you need to change the VFS server and add what you want to do when it is called. Edit “\/usr\/src\/servers\/vfs\/table.c”. You should replace the line “no_sys,\t\/* 64 = unused\t*\/” with: What happens? The method do_TESTCALL will be called when a syscall with number 64 is done.<\/p>\n Change the “\/usr\/src\/servers\/vfs\/proto.h”. Add this: Now you have to create the method in “\/usr\/src\/servers\/vfs\/read.c” (I did in this file and it worked). Add this: <\/p>\n [code lang=”c”] But how to execute? How this works? How to compile? \n$ make libraries\n<\/p><\/blockquote>\n (This process can take a long time) <\/p>\n In “\/usr\/src\/tools” execute:<\/p>\n \n$ make hdboot\n<\/p><\/blockquote>\n Reboot.<\/p>\n How to test and see if it is working? Create in your “\/root” a file with this: int main(int argc, char *argv[]) { Compile it, execute it and done! <\/p>\n This file do a _syscall to FS saying to execute method 64 and send by message the number 2. So the do_TESTCALL receive the parameter and show it on screen. Yes it is simple, but it is just an example about how to work with VFS server. <\/p>\n
\n[code lang=”c”]
\n#define TESTCALL\t 64
\n[\/code]<\/p>\n
\n[code lang=”c”]
\ndo_TESTCALL,\t\/* 64 = unused\t*\/
\n[\/code]<\/p>\n
\n[code lang=”c”]
\n\/* do_TESTCALL EXAMPLE *\/
\n_PROTOTYPE( int do_TESTCALL, (void)\t\t\t\t\t);
\n[\/code]<\/p>\n
\n\/*===========================================================================*
\n *Trabalho:\t\t\tdo_ver_contig\t\t\t\t *
\n *===========================================================================*\/
\nPUBLIC int do_TESTCALL() {
\n message m;
\n printf(“Number received %d”, m_in.fd);
\n}
\n[\/code]<\/p>\n
\nAcess “\/usr\/src\/tools\/” and execute: <\/p>\n
\n[code lang=”c”]
\n#include
\n#include
\n#include
\n int fd = 2;
\n message m;
\n m.m1_i1 = fd;
\n printf(“Number: %d”, fd);
\n _syscall(FS, 64, &m);
\n}
\n[\/code] <\/p>\n