Fix fops write buf printk bug, improve fops file name further

kernel_module/fops.c

@@ -83,11 +83,11 @@ static ssize_t fop_write(struct file *file, const char __user *buf, size_t len,
 				ret = -EFAULT;
 			} else {
 				ret = len;
+				printk(KERN_INFO "buf = %.*s\n", (int)len, data + *off);
 				*off += ret;
 			}
 		}
 	}
-	printk(KERN_INFO "buf = %.*s\n", (int)len, data + *off);
 	printk(KERN_INFO "ret = %lld\n", (long long)ret);
 	return ret;
 }
@@ -144,7 +144,7 @@ int init_module(void)
 		printk(KERN_ALERT "debugfs_create_dir failed");
 		return -1;
 	}
-    file = debugfs_create_file("fops", 0666, dir, NULL, &fops);
+    file = debugfs_create_file("f", 0666, dir, NULL, &fops);
 	if (!file) {
 		printk(KERN_ALERT "debugfs_create_file failed");
 		return -1;

rootfs_overlay/fops.sh

@@ -5,7 +5,7 @@ insmod /fops.ko
 cd /sys/kernel/debug/lkmc_fops
 
 ## Basic read.
-cat fops
+cat f
 # => abcd
 # dmesg => open
 # dmesg => read
@@ -14,14 +14,14 @@ cat fops
 
 ## Basic write
 
-printf '01' >fops
+printf '01' >f
 # dmesg => open
 # dmesg => write
 # dmesg => len = 1
 # dmesg => buf = a
 # dmesg => close
 
-cat fops
+cat f
 # => 01cd
 # dmesg => open
 # dmesg => read
@@ -29,15 +29,15 @@ cat fops
 # dmesg => close
 
 ## ENOSPC
-printf '1234' >fops
-printf '12345' >fops
+printf '1234' >f
+printf '12345' >f
 echo "$?"
 # => 8
-cat fops
+cat f
 # => 1234
 
 ## seek
-printf '1234' >fops
-printf 'z' | dd bs=1 of=fops seek=2
-cat fops
+printf '1234' >f
+printf 'z' | dd bs=1 of=f seek=2
+cat f
 # => 12z4

rootfs_overlay/kgdb-mod.sh

@@ -3,7 +3,7 @@ insmod /fops.ko
 cd /sys/kernel/debug/lkmc_fops
 i=0
 while true; do
-  printf "$i" >fops
+  printf "$i" >f
   i=$(($i+1))
 done &
 /kgdb.sh