more comments

1 files changed, 40 insertions, 36 deletions

diff --git a/proc.h b/proc.h
index d29f765..3f0c006 100644
--- a/proc.h
+++ b/proc.h
@@ -1,18 +1,19 @@
-// segments in proc->gdt
-#define SEG_KCODE 1 // kernel code
-#define SEG_KDATA 2 // kernel data+stack
+// Segments in proc->gdt
+#define SEG_KCODE 1  // kernel code
+#define SEG_KDATA 2  // kernel data+stack
 #define SEG_UCODE 3
 #define SEG_UDATA 4
-#define SEG_TSS   5   // this process's task state
+#define SEG_TSS   5  // this process's task state
 #define NSEGS     6
 
+// Saved registers for kernel context switches.
+// Don't need to save all the %fs etc. segment registers,
+// because they are constant across kernel contexts.
+// Save all the regular registers so we don't need to care
+// which are caller save.
+// Don't save %eax, because that's the return register.
+// The layout of jmpbuf is known to setjmp.S.
 struct jmpbuf {
-  // saved registers for kernel context switches
-  // don't need to save all the fs etc. registers because
-  // they are constant across kernel contexts
-  // save all the regular registers so we don't care which are caller save
-  // don't save eax because that's the return register
-  // layout known to setjmp.S
   int ebx;
   int ecx;
   int edx;
@@ -25,39 +26,42 @@ struct jmpbuf {
 
 enum proc_state { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
 
-struct proc{
-  char *mem;    // start of process's memory (a kernel address)
-    // process memory is laid out contiguously:
-    //   text
-    //   original data and bss
-    //   fixed-size stack
-    //   expandable heap
-  uint sz;      // user memory size
-  char *kstack; // kernel stack
-  enum proc_state state;
-  int pid;
-  int ppid;
-  void *chan; // sleep
-  int killed;
-  struct file *ofile[NOFILE];
-  struct inode *cwd;
-  struct jmpbuf jmpbuf;
-  struct trapframe *tf; // points into kstack, used to find user regs
+// Per-process state
+struct proc {
+  char *mem;                // Start of process memory (kernel address)
+  uint sz;                  // Size of process memory (bytes)
+  char *kstack;             // Bottom of kernel stack for this process
+  enum proc_state state;    // Process state
+  int pid;                  // Process ID
+  int ppid;                 // Parent pid
+  void *chan;               // If non-zero, sleeping on chan
+  int killed;               // If non-zero, have been killed
+  struct file *ofile[NOFILE];  // Open files
+  struct inode *cwd;        // Current directory
+  struct jmpbuf jmpbuf;     // Jump here to run process
+  struct trapframe *tf;     // Trap frame for current interrupt
 };
 
+// Process memory is laid out contiguously:
+//   text
+//   original data and bss
+//   fixed-size stack
+//   expandable heap
+
 extern struct proc proc[];
-extern struct proc *curproc[NCPU];  // can be NULL if no proc running.
+extern struct proc *curproc[NCPU];  // Current (running) process per CPU
 
 #define MPSTACK 512
 
+// Per-CPU state
 struct cpu {
-  uchar apicid;       // Local APIC ID
-  struct jmpbuf jmpbuf;
-  struct taskstate ts;  // only to give cpu address of kernel stack
-  struct segdesc gdt[NSEGS];
-  char mpstack[MPSTACK]; // per-cpu start-up stack
-  volatile int booted;
-  int nlock; // # of locks currently held
+  uchar apicid;               // Local APIC ID
+  struct jmpbuf jmpbuf;       // Jump here to enter scheduler
+  struct taskstate ts;        // Used by x86 to find stack for interrupt
+  struct segdesc gdt[NSEGS];  // x86 global descriptor table
+  char mpstack[MPSTACK];      // Per-CPU startup stack
+  volatile int booted;        // Has the CPU started?
+  int nlock;                  // Number of locks currently held
 };
 
 extern struct cpu cpus[NCPU];