clean up circular buffers, so pipe can queue 512 bytes rather than 511

console.c

@@ -186,9 +186,9 @@ console_write(struct inode *ip, char *buf, int n)
 struct {
   struct spinlock lock;
   char buf[INPUT_BUF];
-  int r;  // Read index
-  int w;  // Write index
-  int e;  // Edit index
+  uint r;  // Read index
+  uint w;  // Write index
+  uint e;  // Edit index
 } input;
 
 #define C(x)  ((x)-'@')  // Control-x
@@ -205,20 +205,20 @@ console_intr(int (*getc)(void))
       procdump();
       break;
     case C('U'):  // Kill line.
-      while(input.e > input.w &&
+      while(input.e != input.w &&
             input.buf[(input.e-1) % INPUT_BUF] != '\n'){
         input.e--;
         cons_putc(BACKSPACE);
       }
       break;
     case C('H'):  // Backspace
-      if(input.e > input.w){
+      if(input.e != input.w){
         input.e--;
         cons_putc(BACKSPACE);
       }
       break;
     default:
-      if(c != 0 && input.e < input.r+INPUT_BUF){
+      if(c != 0 && input.e-input.r < INPUT_BUF){
         input.buf[input.e++ % INPUT_BUF] = c;
         cons_putc(c);
         if(c == '\n' || c == C('D') || input.e == input.r+INPUT_BUF){
@@ -293,7 +293,7 @@ panic(char *s)
   __asm __volatile("cli");
   use_console_lock = 0;
   cprintf("cpu%d: panic: ", cpu());
-  cprintf(s, 0);
+  cprintf(s);
   cprintf("\n");
   getcallerpcs(&s, pcs);
   for(i=0; i<10; i++)

pipe.c

@@ -11,8 +11,8 @@
 struct pipe {
   int readopen;   // read fd is still open
   int writeopen;  // write fd is still open
-  int writep;     // next index to write
-  int readp;      // next index to read
+  uint writep;    // next index to write
+  uint readp;     // next index to read
   struct spinlock lock;
   char data[PIPESIZE];
 };
@@ -83,7 +83,7 @@ pipewrite(struct pipe *p, char *addr, int n)
 
   acquire(&p->lock);
   for(i = 0; i < n; i++){
-    while(((p->writep + 1) % PIPESIZE) == p->readp){
+    while(p->writep == p->readp + PIPESIZE) {
       if(p->readopen == 0 || cp->killed){
         release(&p->lock);
         return -1;
@@ -91,8 +91,7 @@ pipewrite(struct pipe *p, char *addr, int n)
       wakeup(&p->readp);
       sleep(&p->writep, &p->lock);
     }
-    p->data[p->writep] = addr[i];
-    p->writep = (p->writep + 1) % PIPESIZE;
+    p->data[p->writep++ % PIPESIZE] = addr[i];
   }
   wakeup(&p->readp);
   release(&p->lock);
@@ -115,8 +114,7 @@ piperead(struct pipe *p, char *addr, int n)
   for(i = 0; i < n; i++){
     if(p->readp == p->writep)
       break;
-    addr[i] = p->data[p->readp];
-    p->readp = (p->readp + 1) % PIPESIZE;
+    addr[i] = p->data[p->readp++ % PIPESIZE];
   }
   wakeup(&p->writep);
   release(&p->lock);