From: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Date: Tue, 8 Dec 2009 17:58:11 +0000 (-0200)
Subject: Control size of buffer.
X-Git-Url: http://git.cascardo.info/?p=cascardo%2Fkernel%2Fsamples%2F02.char%2F.git;a=commitdiff_plain;h=0f97392e9082dbf08807986bad7e1a20e781a807;ds=sidebyside

Control size of buffer.
---

diff --git a/helloc.c b/helloc.c
index f43a767..9f983a2 100644
--- a/helloc.c
+++ b/helloc.c
@@ -31,6 +31,14 @@ static int helloc_open(struct inode *ino, struct file *filp)
 		return -ENODEV;
 	msg = hello_message[iminor(ino)];
 	filp->private_data = msg;
+	if (filp->f_flags & O_TRUNC) {
+		memset(msg->text, 0, msg->len);
+		msg->len = 0;
+		printk(KERN_INFO "File opened with truncate flags\n");
+	}
+	if (filp->f_flags & O_APPEND) {
+		filp->f_pos = msg->len;
+	}
 	return 0;
 }
 
@@ -67,18 +75,27 @@ static ssize_t helloc_write(struct file *filp, const char __user *buf,
 	int r;
 	struct message *msg = filp->private_data;
 	/* do not read pass through the size of the message */
-	if (*pos >= msg->len)
+	if (*pos >= BUFFER_SIZE)
 	/* return end of file */
 		return 0;
 	/* if len is bigger than the rest of the message, clamp it */
-	if (len > msg->len - *pos)
-		len = msg->len - *pos;
+	if (len > BUFFER_SIZE - *pos)
+		len = BUFFER_SIZE - *pos;
+
 	/* copy message to user space and return error if it fails */
 	r = copy_from_user(msg->text + *pos, buf, len);
-	if (r)
+	if (r) {
+		if (*pos + len > msg->len)
+			memset(msg->text + msg->len, 0, *pos + len - msg->len);
 		return -EFAULT;
+	}
 	/* update the file position */
 	*pos += len;
+	if (msg->len < *pos) {
+		printk(KERN_DEBUG "Updating size from %d to %lld\n", msg->len, *pos);
+		msg->len = *pos;
+	}
+
 	return len;
 }