El Fri, Feb 27, 2009 at 07:38:59PM +0530 Sabin ha dit:
> I saw the following code:
> static int uart_read_proc(char *page, char **start, off_t off,
> int count, int *eof, void *data)
> {
> struct tty_driver *ttydrv = data;
> struct uart_driver *drv = ttydrv->driver_state;
> int i, len = 0, l;
> off_t begin = 0;
>
> len += sprintf(page, "serinfo:1.0 driver%s%s revision:%s\n",
> "", "", "");
>
> I dont understand why sprintf is used and not copy_to_user?
> When we write a module/driver we treat both read and write buffer as
> coming from userspace and hence use put_user/get_user or
> copy_from_user/copy_to_user.
> Anybody has any idea why proc read is handled differently?
good observation!
the read_proc function of an proc entry is called from
proc_file_read(), which passes it a non-userspace
buffer. proc_file_read() is in charge of copying the data from this
buffer to the buffer provided by userspace:
http://lxr.linux.no/linux+v2.6.28/fs/proc/generic.c#L41
write_proc on the other receives a user space buffer from
proc_file_write() and is therefore required to use copy_from_user() or
get_user():
http://lxr.linux.no/linux+v2.6.28/fs/proc/generic.c#L187
--
Matthias Kaehlcke
Embedded Linux Engineer
Barcelona
Usually when people are sad, they don't do anything. They just cry over
their condition. But when they get angry, they bring about a change
(Malcolm X)
.''`.
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