xv6-cs450/proc.h

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// Segments in proc->gdt.
#define NSEGS 7
#define NO_OF_SYSCALLS 22
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// Per-CPU state
struct cpu {
uchar id; // Local APIC ID; index into cpus[] below
struct context *scheduler; // swtch() here to enter scheduler
struct taskstate ts; // Used by x86 to find stack for interrupt
struct segdesc gdt[NSEGS]; // x86 global descriptor table
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volatile uint started; // Has the CPU started?
int ncli; // Depth of pushcli nesting.
int intena; // Were interrupts enabled before pushcli?
// Cpu-local storage variables; see below
struct cpu *cpu;
struct proc *proc; // The currently-running process.
};
extern struct cpu cpus[NCPU];
extern int ncpu;
// Per-CPU variables, holding pointers to the
// current cpu and to the current process.
// The asm suffix tells gcc to use "%gs:0" to refer to cpu
// and "%gs:4" to refer to proc. seginit sets up the
// %gs segment register so that %gs refers to the memory
// holding those two variables in the local cpu's struct cpu.
// This is similar to how thread-local variables are implemented
// in thread libraries such as Linux pthreads.
extern struct cpu *cpu asm("%gs:0"); // &cpus[cpunum()]
extern struct proc *proc asm("%gs:4"); // cpus[cpunum()].proc
//PAGEBREAK: 17
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// Saved registers for kernel context switches.
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// Don't need to save all the segment registers (%cs, etc),
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// because they are constant across kernel contexts.
// Don't need to save %eax, %ecx, %edx, because the
// x86 convention is that the caller has saved them.
// Contexts are stored at the bottom of the stack they
// describe; the stack pointer is the address of the context.
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// The layout of the context matches the layout of the stack in swtch.S
// at the "Switch stacks" comment. Switch doesn't save eip explicitly,
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// but it is on the stack and allocproc() manipulates it.
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struct context {
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uint edi;
uint esi;
uint ebx;
uint ebp;
uint eip;
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};
enum procstate { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
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// Per-process state
struct proc {
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uint sz; // Size of process memory (bytes)
pde_t* pgdir; // Page table
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char *kstack; // Bottom of kernel stack for this process
enum procstate state; // Process state
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volatile int pid; // Process ID
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struct proc *parent; // Parent process
struct trapframe *tf; // Trap frame for current syscall
struct context *context; // swtch() here to run process
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void *chan; // If non-zero, sleeping on chan
int killed; // If non-zero, have been killed
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struct file *ofile[NOFILE]; // Open files
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struct inode *cwd; // Current directory
char name[16]; // Process name (debugging)
uint syscall_count[NO_OF_SYSCALLS]; // Number of particular syscalls
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};
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// Process memory is laid out contiguously, low addresses first:
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// text
// original data and bss
// fixed-size stack
// expandable heap