- copy_to_user vs sprintf
- Posted by Hagit on January 28th, 2004
I just cant get it!
I wrote a module that created its own entry in the /proc file system.
My module implemented read and write functions. When the user call
read(fd, &buff, 1) I am trying to copy to the user buff the character
B. When I use the
copy_to_user() function, the user doesnt get my B, but when I use the
sprintf() function the user gets the B. I cant understand it. what is
wrong???
The relevant calls are described below:
char raed_info = 'B';
copy_to_user(page, &read_info, sizeof(read_info));
sprintf(page,"%c",read_info);
Thanks
Hagit
- Posted by Victor Nazarov on January 28th, 2004
Hagit wrote:
I assume this to be `read_info'
in the read(fd, &buff, 1) call you must supply only one char to user,
but sprintf writes 2 ('B', '\0') so it's not right way.
Why don't you use memcpy (page, &read_info, sizeof (read_info)). I think
this should work.
copy_to_user seems to be not Standart C Library function neither POSIX
one. What is the code?
Vir
- Posted by Dances With Crows on January 28th, 2004
On Wed, 28 Jan 2004 16:34:14 +0300, Victor Nazarov staggered into the
Black Sun and said:
Yeah, if it was mispelled in the actual code, Hagit would've gotten a
snytax error.
FWIW, I had a look in /usr/src/linux/drivers/char/rtc.c , where they use
sprintf() instead of copy_to_user() when the user reads the /proc entry.
In that particular module, copy_to_user is only used once, in the
rtc_ioctl function.
copy_to_user is a Linux-kernel specific function that copies data from
kernel space to user space. It's used all over the place and is defined
in /usr/src/linux/include/asm-i386/uaccess.h for the x86, at least.
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