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Old 06-22-2009, 03:39 AM   #1
LQ Newbie
Registered: Jan 2009
Posts: 1

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Angry i am using write() function to send string to my driver . it returns EFAULT.

hi ,
i am using write() function to send strings from a 2d array to driver using a repeated loop. it succeeds in its operation .but out of 100 tests at least 1 time it is unable to send the strings to driver & at that time perror in user application returns "Bad address" error.

here is the application code chunk:
int sel_menuitem(char (*item)[20],unsigned char max_items,unsigned char onscrn_max_item,unsigned char crsr_xloc
,unsigned char item_xloc,unsigned char item_yloc,unsigned char item_size,unsigned char hold,unsigned char prev_stat) {

int i;
int status;
unsigned char sel_complete=0;
int ret = -1;
char retry = 0;
unsigned long temp = 0;

for(i=0;i<max_items;i++) {

temp = strlen(item+i)|(item_xloc<<8)|((item_yloc+i)<<16);
status = write(lcd_fd, (item+i), temp);
printf("item1 %s<%d>\n",(item+i),strlen((item+i)));
if(status < 0)
perror("Write ");


function receives 2d array of cracters . temp is the variable which contains string length ,x location of string to display,y location of string to display.

here is the driver write method:
static int lcd_write(struct file* fd_LCD, const char __user* UserBuff,size_t count,loff_t* off) {

char *Driver_Buff;
unsigned char Xpos;
unsigned char Ypos;
int ret;
printk(KERN_ERR ".1d<%d>\n",strlen(UserBuff));
if(strlen(UserBuff) != 0) {


string_len = 20;
/* whether offset is beyond one line */
string_len = 21-Xpos;

printk(KERN_ERR ".2d<%d>\n",string_len);

Driver_Buff = (char*)kmalloc(string_len,GFP_KERNEL);
memset(Driver_Buff, 0, sizeof(Driver_Buff));

/* if highlight is not enabled for the data */
if(Line_Highlight!=1) {
ret = copy_from_user(Driver_Buff,UserBuff,string_len);
printk(KERN_ERR "while read1<%d><%s>\n",ret,Driver_Buff);
if(ret) {
printk(KERN_ERR "0>!-EFAULT!\n");
return -EFAULT;
// printk(KERN_ERR "driver:received item,count %s <%d>\n",Driver_Buff,string_len);

count contains string length,x location,y location . i am extracting the information & try to write to my lcd

any helps are appreciated...


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