From 03f3d956103dd6149a3c62ab67ec323386e32862 Mon Sep 17 00:00:00 2001
From: stamrakar <stamrakar@Ubuntu.myguest.virtualbox.org>
Date: Mon, 4 Nov 2024 16:54:57 -0700
Subject: [PATCH] Supporting llseek() and unlocked_ioctl()

---
 aesd-char-driver/main.c | 104 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 103 insertions(+), 1 deletion(-)

diff --git a/aesd-char-driver/main.c b/aesd-char-driver/main.c
index 6bbb86b..1413277 100644
--- a/aesd-char-driver/main.c
+++ b/aesd-char-driver/main.c
@@ -28,7 +28,7 @@
 #include <linux/uaccess.h>
 #include <linux/fs.h> // file_operations
 
-
+#include "aesd_ioctl.h"
 #include "aesdchar.h"
 
 
@@ -71,6 +71,106 @@ int aesd_release(struct inode *inode, struct file *filp)
     return 0;
 }
 
+/**
+ * "The llseek method is used to change the current read/write position
+ * in a file, and the new position is returne as a (positive) return value.
+ * The loff_t parameter is a "long offset" and is at least 64 bits wide 
+ * even on 32-bit platforms. Errors are signaled by a negative return value.
+ * If this function pointer is NULL, seek calls will modify the position
+ * counter in the file structure in potentially unpredictable ways."
+ * Linux Device Drivers Chapter 3, J. Corbet, A Rubini, G. Kroah-Hartman
+ */
+loff_t aesd_llseek(struct file *filp, loff_t offset, int whence)
+{
+    ssize_t retval;
+    loff_t fsl;
+    loff_t circbuffsize=0;
+    struct aesd_dev *dev = NULL;
+    struct aesd_buffer_entry *entry = NULL;
+    uint8_t stread;
+    if (filp == NULL)
+    {
+        retval = -EINVAL;
+        PDEBUG("file pointer filp NULL, returning %zu", retval);
+        goto errout;
+    }
+
+    dev = filp->private_data;
+
+    if (mutex_lock_interruptible(&dev->bufferlock))
+    {
+        retval = -ERESTARTSYS;
+        PDEBUG("mutex lock interruptible, returning %zu", retval);
+        goto errout;
+    }
+
+    AESD_CIRCULAR_BUFFER_FOREACH(entry, &(aesd_device.circular), stread)
+    {
+        if(entry->buffptr != NULL)
+            circbuffsize += entry->size;
+    }
+
+    //need to get the total size of all content of the circular buffer
+    fsl = fixed_size_llseek(filp, offset, whence, circbuffsize);
+    if (fsl == -EINVAL)
+    {
+        retval = fsl;
+        PDEBUG("fixed_size_llseek() returned -EINVAL. %zu", retval);
+        goto unlockout;
+    }
+    retval = fsl;
+    //filp->f_pos += fsl;
+    return retval;
+
+    unlockout:
+    mutex_unlock(&dev->bufferlock);
+    errout:
+    return retval;
+}
+
+
+/**
+ * Adjust the file offset (f_pos) parameter of @param filp based on the location specified by
+ * @param write_cmd (the zero referenced command to locate) and @param write_cmd_offset
+ * (the zero referenced offset into the command) 
+ * @return 0 if successful, negative if error occurred:
+ *      -ERESTARTSYS if mutex could not be obtained
+ *      -EINVAL if write command or write_cmd_offset was out of range.
+ */
+static long aesd_adjust_file_offset(struct file *filp, unsigned int write_cmd, unsigned int write_cmd_offset)
+{
+
+}
+
+int aesd_unlocked_ioctl(struct inode *node, struct file *filp, unsigned int vala, unsigned long valb)
+{
+    ssize_t retval; 
+    if (filp == NULL)
+    {
+        retval = -EINVAL;
+        PDEBUG("file pointer filp NULL, returning %zu", retval);
+        goto errout;
+    }
+    
+    case AESDCHAR_IOCSEEKTO
+    {
+        struct aesd_seekto seekto;
+        if (copy_from_user(&seekto, (const void __user *)arg, sizeof(seekto)) != 0) {
+            retval = EFAULT;
+        } else {
+            retval = aesd_adjust_file_offset(filp, seekto.write_cmd, seekto.write_cmd_offset);
+        }
+        break;
+    }
+
+    default:
+        break;
+
+
+    errout:
+    return retval;
+}
+
 ssize_t aesd_read(struct file *filp, char __user *buf, size_t count,
                 loff_t *f_pos)
 {
@@ -243,6 +343,8 @@ struct file_operations aesd_fops = {
     .write =    aesd_write,
     .open =     aesd_open,
     .release =  aesd_release,
+    .llseek =   aesd_llseek,
+    .unlocked_ioctl = aesd_unlocked_ioctl,
 };
 
 static int aesd_setup_cdev(struct aesd_dev *dev)