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1 #include "types.h"
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2 #include "defs.h"
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3 #include "param.h"
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4 #include "memlayout.h"
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5 #include "mmu.h"
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6 #include "arm.h"
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7 #include "proc.h"
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8 #include "spinlock.h"
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9
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10 //
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11 // Process initialization:
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12 // process initialize is somewhat tricky.
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13 // 1. We need to fake the kernel stack of a new process as if the process
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14 // has been interrupt (a trapframe on the stack), this would allow us
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15 // to "return" to the correct user instruction.
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16 // 2. We also need to fake the kernel execution for this new process. When
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17 // swtch switches to this (new) process, it will switch to its stack,
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18 // and reload registers with the saved context. We use forkret as the
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19 // return address (in lr register). (In x86, it will be the return address
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20 // pushed on the stack by the process.)
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21 //
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22 // The design of context switch in xv6 is interesting: after initialization,
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23 // each CPU executes in the scheduler() function. The context switch is not
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24 // between two processes, but instead, between the scheduler. Think of scheduler
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25 // as the idle process.
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26 //
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27 struct {
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28 struct spinlock lock;
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29 struct proc proc[NPROC];
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30 } ptable;
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31
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32 static struct proc *initproc;
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33 struct proc *proc;
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34
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35 int nextpid = 1;
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36 extern void forkret(void);
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37 extern void trapret(void);
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38
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39 static void wakeup1(void *chan);
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40
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41 void pinit(void)
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42 {
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43 initlock(&ptable.lock, "ptable");
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44 }
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45
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46 //PAGEBREAK: 32
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47 // Look in the process table for an UNUSED proc.
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48 // If found, change state to EMBRYO and initialize
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49 // state required to run in the kernel.
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50 // Otherwise return 0.
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51 static struct proc* allocproc(void)
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52 {
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53 struct proc *p;
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54 char *sp;
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55
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56 acquire(&ptable.lock);
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57
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58 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++) {
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59 if(p->state == UNUSED) {
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60 goto found;
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61 }
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62
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63 }
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64
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65 release(&ptable.lock);
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66 return 0;
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67
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68 found:
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69 p->state = EMBRYO;
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70 p->pid = nextpid++;
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71 release(&ptable.lock);
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72
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73 // Allocate kernel stack.
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74 if((p->kstack = alloc_page ()) == 0){
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75 p->state = UNUSED;
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76 return 0;
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77 }
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78
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79 sp = p->kstack + KSTACKSIZE;
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80
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81 // Leave room for trap frame.
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82 sp -= sizeof (*p->tf);
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83 p->tf = (struct trapframe*)sp;
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84
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85 // Set up new context to start executing at forkret,
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86 // which returns to trapret.
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87 sp -= 4;
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88 *(uint*)sp = (uint)trapret;
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89
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90 sp -= 4;
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91 *(uint*)sp = (uint)p->kstack + KSTACKSIZE;
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92
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93 sp -= sizeof (*p->context);
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94 p->context = (struct context*)sp;
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95 memset(p->context, 0, sizeof(*p->context));
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96
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97 // skip the push {fp, lr} instruction in the prologue of forkret.
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98 // This is different from x86, in which the harderware pushes return
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99 // address before executing the callee. In ARM, return address is
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100 // loaded into the lr register, and push to the stack by the callee
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101 // (if and when necessary). We need to skip that instruction and let
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102 // it use our implementation.
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103 p->context->lr = (uint)forkret+4;
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104
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105 return p;
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106 }
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107
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108 void error_init ()
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109 {
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110 panic ("failed to craft first process\n");
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111 }
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112
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113
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114 //PAGEBREAK: 32
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115 // hand-craft the first user process. We link initcode.S into the kernel
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116 // as a binary, the linker will generate __binary_initcode_start/_size
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117 void userinit(void)
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118 {
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119 struct proc *p;
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120 extern char _binary_initcode_start[], _binary_initcode_size[];
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121
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122 p = allocproc();
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123 initproc = p;
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124
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125 if((p->pgdir = kpt_alloc()) == NULL) {
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126 panic("userinit: out of memory?");
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127 }
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128
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129 inituvm(p->pgdir, _binary_initcode_start, (int)_binary_initcode_size);
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130
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131 p->sz = PTE_SZ;
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132
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133 // craft the trapframe as if
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134 memset(p->tf, 0, sizeof(*p->tf));
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135
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136 p->tf->r14_svc = (uint)error_init;
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137 p->tf->spsr = spsr_usr ();
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138 p->tf->sp_usr = PTE_SZ; // set the user stack
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139 p->tf->lr_usr = 0;
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140
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141 // set the user pc. The actual pc loaded into r15_usr is in
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142 // p->tf, the trapframe.
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143 p->tf->pc = 0; // beginning of initcode.S
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144
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145 safestrcpy(p->name, "initcode", sizeof(p->name));
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146 p->cwd = namei("/");
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147
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148 p->state = RUNNABLE;
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149 }
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150
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151 // Grow current process's memory by n bytes.
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152 // Return 0 on success, -1 on failure.
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153 int growproc(int n)
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154 {
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155 uint sz;
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156
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157 sz = proc->sz;
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158
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159 if(n > 0){
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160 if((sz = allocuvm(proc->pgdir, sz, sz + n)) == 0) {
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161 return -1;
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162 }
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163
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164 } else if(n < 0){
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165 if((sz = deallocuvm(proc->pgdir, sz, sz + n)) == 0) {
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166 return -1;
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167 }
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168 }
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169
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170 proc->sz = sz;
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171 switchuvm(proc);
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172
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173 return 0;
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174 }
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175
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176 // Create a new process copying p as the parent.
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177 // Sets up stack to return as if from system call.
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178 // Caller must set state of returned proc to RUNNABLE.
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179 int fork(void)
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180 {
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181 int i, pid;
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182 struct proc *np;
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183
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184 // Allocate process.
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185 if((np = allocproc()) == 0) {
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186 return -1;
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187 }
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188
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189 // Copy process state from p.
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190 if((np->pgdir = copyuvm(proc->pgdir, proc->sz)) == 0){
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191 free_page(np->kstack);
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192 np->kstack = 0;
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193 np->state = UNUSED;
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194 return -1;
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195 }
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196
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197 np->sz = proc->sz;
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198 np->parent = proc;
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199 *np->tf = *proc->tf;
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200
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201 // Clear r0 so that fork returns 0 in the child.
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202 np->tf->r0 = 0;
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203
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204 for(i = 0; i < NOFILE; i++) {
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205 if(proc->ofile[i]) {
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206 np->ofile[i] = filedup(proc->ofile[i]);
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207 }
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208 }
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209
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210 np->cwd = idup(proc->cwd);
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211
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212 pid = np->pid;
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213 np->state = RUNNABLE;
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214 safestrcpy(np->name, proc->name, sizeof(proc->name));
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215
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216 return pid;
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217 }
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218
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219 // Exit the current process. Does not return.
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220 // An exited process remains in the zombie state
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221 // until its parent calls wait() to find out it exited.
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222 void exit(void)
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223 {
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224 struct proc *p;
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225 int fd;
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226
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227 if(proc == initproc) {
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228 panic("init exiting");
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229 }
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230
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231 // Close all open files.
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232 for(fd = 0; fd < NOFILE; fd++){
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233 if(proc->ofile[fd]){
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234 fileclose(proc->ofile[fd]);
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235 proc->ofile[fd] = 0;
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236 }
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237 }
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238
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239 iput(proc->cwd);
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240 proc->cwd = 0;
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241
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242 acquire(&ptable.lock);
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243
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244 // Parent might be sleeping in wait().
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245 wakeup1(proc->parent);
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246
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247 // Pass abandoned children to init.
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248 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
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249 if(p->parent == proc){
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250 p->parent = initproc;
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251
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252 if(p->state == ZOMBIE) {
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253 wakeup1(initproc);
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254 }
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255 }
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256 }
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257
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258 // Jump into the scheduler, never to return.
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259 proc->state = ZOMBIE;
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260 sched();
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261
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262 panic("zombie exit");
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263 }
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264
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265 // Wait for a child process to exit and return its pid.
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266 // Return -1 if this process has no children.
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267 int wait(void)
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268 {
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269 struct proc *p;
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270 int havekids, pid;
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271
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272 acquire(&ptable.lock);
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273
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274 for(;;){
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275 // Scan through table looking for zombie children.
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276 havekids = 0;
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277
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278 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
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279 if(p->parent != proc) {
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280 continue;
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281 }
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282
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283 havekids = 1;
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284
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285 if(p->state == ZOMBIE){
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286 // Found one.
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287 pid = p->pid;
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288 free_page(p->kstack);
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289 p->kstack = 0;
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290 freevm(p->pgdir);
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291 p->state = UNUSED;
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292 p->pid = 0;
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293 p->parent = 0;
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294 p->name[0] = 0;
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295 p->killed = 0;
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296 release(&ptable.lock);
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297
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298 return pid;
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299 }
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300 }
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301
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302 // No point waiting if we don't have any children.
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303 if(!havekids || proc->killed){
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304 release(&ptable.lock);
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305 return -1;
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306 }
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307
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308 // Wait for children to exit. (See wakeup1 call in proc_exit.)
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309 sleep(proc, &ptable.lock); //DOC: wait-sleep
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310 }
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311 }
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312
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313 //PAGEBREAK: 42
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314 // Per-CPU process scheduler.
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315 // Each CPU calls scheduler() after setting itself up.
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316 // Scheduler never returns. It loops, doing:
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317 // - choose a process to run
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318 // - swtch to start running that process
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319 // - eventually that process transfers control
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320 // via swtch back to the scheduler.
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321 void scheduler(void)
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322 {
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323 struct proc *p;
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324
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325 for(;;){
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326 // Enable interrupts on this processor.
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327 sti();
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328
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329 // Loop over process table looking for process to run.
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330 acquire(&ptable.lock);
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331
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332 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
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333 if(p->state != RUNNABLE) {
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334 continue;
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335 }
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336
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337 // Switch to chosen process. It is the process's job
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338 // to release ptable.lock and then reacquire it
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339 // before jumping back to us.
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340 proc = p;
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341 switchuvm(p);
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342
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343 p->state = RUNNING;
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344
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345 swtch(&cpu->scheduler, proc->context);
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346 // Process is done running for now.
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347 // It should have changed its p->state before coming back.
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348 proc = 0;
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349 }
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350
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351 release(&ptable.lock);
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352 }
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353 }
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354
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355 // Enter scheduler. Must hold only ptable.lock
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356 // and have changed proc->state.
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357 void sched(void)
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358 {
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359 int intena;
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360
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361 //show_callstk ("sched");
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362
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363 if(!holding(&ptable.lock)) {
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364 panic("sched ptable.lock");
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365 }
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366
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367 if(cpu->ncli != 1) {
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368 panic("sched locks");
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369 }
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370
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371 if(proc->state == RUNNING) {
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372 panic("sched running");
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373 }
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374
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375 if(int_enabled ()) {
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376 panic("sched interruptible");
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377 }
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378
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379 intena = cpu->intena;
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380 swtch(&proc->context, cpu->scheduler);
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381 cpu->intena = intena;
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382 }
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383
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384 // Give up the CPU for one scheduling round.
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385 void yield(void)
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386 {
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387 acquire(&ptable.lock); //DOC: yieldlock
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388 proc->state = RUNNABLE;
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389 sched();
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390 release(&ptable.lock);
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391 }
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392
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393 // A fork child's very first scheduling by scheduler()
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394 // will swtch here. "Return" to user space.
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395 void forkret(void)
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396 {
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397 static int first = 1;
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398
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399 // Still holding ptable.lock from scheduler.
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400 release(&ptable.lock);
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401
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402 if (first) {
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403 // Some initialization functions must be run in the context
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404 // of a regular process (e.g., they call sleep), and thus cannot
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405 // be run from main().
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406 first = 0;
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407 initlog();
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408 }
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409
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410 // Return to "caller", actually trapret (see allocproc).
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411 }
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412
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413 // Atomically release lock and sleep on chan.
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414 // Reacquires lock when awakened.
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415 void sleep(void *chan, struct spinlock *lk)
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416 {
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417 //show_callstk("sleep");
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418
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419 if(proc == 0) {
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420 panic("sleep");
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421 }
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422
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423 if(lk == 0) {
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424 panic("sleep without lk");
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425 }
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426
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427 // Must acquire ptable.lock in order to change p->state and then call
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428 // sched. Once we hold ptable.lock, we can be guaranteed that we won't
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429 // miss any wakeup (wakeup runs with ptable.lock locked), so it's okay
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430 // to release lk.
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431 if(lk != &ptable.lock){ //DOC: sleeplock0
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432 acquire(&ptable.lock); //DOC: sleeplock1
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433 release(lk);
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434 }
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435
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436 // Go to sleep.
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437 proc->chan = chan;
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438 proc->state = SLEEPING;
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439 sched();
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440
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441 // Tidy up.
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442 proc->chan = 0;
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443
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444 // Reacquire original lock.
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445 if(lk != &ptable.lock){ //DOC: sleeplock2
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446 release(&ptable.lock);
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447 acquire(lk);
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448 }
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449 }
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450
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451 //PAGEBREAK!
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452 // Wake up all processes sleeping on chan. The ptable lock must be held.
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453 static void wakeup1(void *chan)
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454 {
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455 struct proc *p;
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456
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457 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++) {
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458 if(p->state == SLEEPING && p->chan == chan) {
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459 p->state = RUNNABLE;
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460 }
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461 }
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462 }
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463
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464 // Wake up all processes sleeping on chan.
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465 void wakeup(void *chan)
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466 {
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467 acquire(&ptable.lock);
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468 wakeup1(chan);
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469 release(&ptable.lock);
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470 }
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471
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472 // Kill the process with the given pid. Process won't exit until it returns
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473 // to user space (see trap in trap.c).
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474 int kill(int pid)
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475 {
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476 struct proc *p;
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477
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478 acquire(&ptable.lock);
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479
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480 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
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481 if(p->pid == pid){
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482 p->killed = 1;
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483
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484 // Wake process from sleep if necessary.
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485 if(p->state == SLEEPING) {
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486 p->state = RUNNABLE;
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487 }
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488
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489 release(&ptable.lock);
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490 return 0;
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491 }
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492 }
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493
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494 release(&ptable.lock);
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495 return -1;
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496 }
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497
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498 //PAGEBREAK: 36
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499 // Print a process listing to console. For debugging. Runs when user
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500 // types ^P on console. No lock to avoid wedging a stuck machine further.
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501 void procdump(void)
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502 {
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503 static char *states[] = {
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504 [UNUSED] "unused",
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505 [EMBRYO] "embryo",
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506 [SLEEPING] "sleep ",
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507 [RUNNABLE] "runble",
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508 [RUNNING] "run ",
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509 [ZOMBIE] "zombie"
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510 };
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511
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512 struct proc *p;
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513 char *state;
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514
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515 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
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516 if(p->state == UNUSED) {
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517 continue;
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518 }
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519
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520 if(p->state >= 0 && p->state < NELEM(states) && states[p->state]) {
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521 state = states[p->state];
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522 } else {
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523 state = "???";
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524 }
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525
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526 cprintf("%d %s %d:%s %d\n", p->pid, state, p->pid, p->name, p->parent->pid);
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527 }
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528
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529 show_callstk("procdump: \n");
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|
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530 }
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531
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532
|
