fix improper ptr check, fix offset calc, ratelimit printk messages

2 files changed, 17 insertions, 9 deletions

diff --git a/main.c b/main.c
index 7036144..579a621 100644
--- a/main.c
+++ b/main.c
@@ -146,7 +146,7 @@ static int hello_trim(struct hello_dev *dev)
 static struct hello_ll *hello_follow(struct hello_dev *dev, int n)
 {
 	struct hello_ll *nptr = dev->mylist, *tmp;
-    PDEBUG("follow() called with n: %i\n", n);
+    PRDEBUG("follow() called with n: %i\n", n);
 
     /* allocate first node explicitly if it needs to be */
     if (!nptr) {
@@ -162,8 +162,12 @@ static struct hello_ll *hello_follow(struct hello_dev *dev, int n)
     /* follow the list */
     while (n--) {
         /* almost like testing for NULL, remember this is circular list */
-        if (nptr->list.next == &nptr->list) {
-            PDEBUG("allocating additional node");
+        PRDEBUG("while loop: n is: %i, nptr->list is at: %p, ntpr->list.next is at %p\n",
+            n, /* &nptr->list */ &dev->mylist->list, nptr->list.next);
+
+        /* there was a bug below, took 2 hours to track down */
+        if (nptr->list.next == /* &nptr->list */ &dev->mylist->list) {
+            PRDEBUG("allocating additional node");
             tmp = kmalloc(sizeof(struct hello_ll), GFP_KERNEL);
             if (!tmp)
                 return NULL;
@@ -187,7 +191,7 @@ static ssize_t hello_read(struct file *filp, char __user *buff, size_t count, lo
     ssize_t ret = 0; /* end of file, also in case of out of bound */
     struct hello_ll *cptr = NULL; /* node where right chunk is */
     int chunk_pos = 0;
-    PDEBUG("read() called\n");
+    PRDEBUG("read() called\n");
 
     if (down_interruptible(&dev->sem))
         return -ERESTARTSYS;
@@ -220,7 +224,7 @@ static ssize_t hello_read(struct file *filp, char __user *buff, size_t count, lo
         count = dev->chunk_sz - chunk_pos;
 
     /* write to userspace memory by reading only up to the end of chunk */
-    if (copy_to_user(buff, cptr->chunk + (*f_pos % dev->chunk_sz), count))
+    if (copy_to_user(buff, cptr->chunk + chunk_pos, count))
     {
         ret = -EFAULT;
         goto out;
@@ -240,12 +244,12 @@ static ssize_t hello_write(struct file *filp, const char __user *buff, size_t co
     ssize_t ret = -ENOMEM;
     struct hello_ll *cptr = NULL; /* node where right chunk is */
     int chunk_pos = 0;
-    PDEBUG("write() called\n");
+    PRDEBUG("write() called, user buffer is at: %p, f_pos: %lli, c: %lu\n", buff, *f_pos, count);
 
     if (down_interruptible(&dev->sem))
         return -ERESTARTSYS;
 
-    chunk_pos = *f_pos / dev->chunk_sz;
+    chunk_pos = *f_pos % dev->chunk_sz;
 
     cptr = hello_follow(dev, *f_pos / dev->chunk_sz);
     if (!cptr)
@@ -342,7 +346,7 @@ static int __init hello_init(void)
         ret = alloc_chrdev_region(&devnum, 0 /* first minor */, 1, "helloc");
         hello_major = MAJOR(devnum);
         hello_minor = MINOR(devnum);
-        printk(KERN_INFO "[hello] major: %d, minor: %d\n", hello_major, hello_minor);
+        PDEBUG("[hello] major: %d, minor: %d\n", hello_major, hello_minor);
     }
     if (ret < 0) {
         printk(KERN_WARNING "[hello] can't get the major %d number\n", hello_major);
diff --git a/main.h b/main.h
index cb751d0..e2727db 100644
--- a/main.h
+++ b/main.h
@@ -9,8 +9,12 @@
  */
 #ifdef HELLO_DEBUG
   #define PDEBUG(fmt, args...) printk( KERN_DEBUG "[hello] " fmt, ##args)
+  #define PRDEBUG(fmt, args...) if (printk_ratelimit()) \
+                                    printk( KERN_DEBUG "[hello] " fmt, ##args)
 #else
-  #define PDEBUG(fmt, args...) /* not debugging: nothing */
+  /* not debugging: nothing */
+  #define PDEBUG(fmt, args...)
+  #define PRDEBUG(fmt, args...)
 #endif
 
 #ifndef HELLO_MAJOR