On 10/1/05, raja <vnagaraju@xxxxxxxxxxxx> wrote: > yaa,thank you, > I agree with you but,here we are specifying the value for quantum to be > set with. > I thing here instead of _IO we have to use _IOW() and we have to specify > the lat parameter as int? > Am i right? > Wht is wrong with me? I think you're confusing what means data transfer between kernel and userspace. #define SCULL_IOCSQUANTUM _IOW(SCULL_IOC_MAGIC, 1, int) #define SCULL_IOCTQUANTUM _IO(SCULL_IOC_MAGIC, 3) do the same thing, but IOCS gets the value to set through a pointer, id est, using data transfer. IOCT gets the value directly from the argument value, it doesn't use that data transfer. There is a write to the former. There's not a write to the latter. I thinks this confusing wouldn't lead you to create a buggy module since the macros just use it to create a unique number, and this unique number will be create whatever macro you choose. But creating ioctl mistakes-free modules makes these things worthy to pay attention. If someone see any mistakes from me, please notify me. Regards, Riba > > > thanks in advance > raja > > > > On Sat, 2005-10-01 at 00:29 -0300, Ribamar Santarosa de Sousa wrote: > > On 9/30/05, raja <vnagaraju@xxxxxxxxxxxx> wrote: > > > Hi, > > > I am writing a character device driver similar to that in the book LDD3 > > > by rubini.While undersatnding the code I have got some doubt regarding > > > the ioctl implemtntation. > > > In scull.h file it is defined SCULL_IOCTQUANTUM as > > > #define SCULL_IOCTQUANTUM _IO(SCULL_IOC_MAGIC, 3) > > > here while defining there is no arguments for this call. > > > But while implementing that in the ioctl call > > > > > > case SCULL_IOCTQUANTUM: /* Tell: arg is the value */ > > > if (! capable (CAP_SYS_ADMIN)) > > > return -EPERM; > > > scull_quantum = arg; > > > break; > > > > > > but here arg is assigned to scull_quantum.is it the correct?I > > > > Why not? : - ) Using the logic, do you think it need or doesn't need > > the arg? Of course it need, or it'd have no functionality! > > > > See: for the line > > #define SCULL_IOCTQUANTUM _IO(SCULL_IOC_MAGIC, 3) > > the macro (do you understand well what is a macro?) _IO (defined in > > <asm/ioctl.h> ) will operate the parameters SCULL_IOC_MAGIC and 3 to > > create -- in compilation time, not in run time -- a unique ioctl > > number N. This number N is, so, associated to SCULL_IOCTQUANTUM, as > > it was 'SCULL_IOCTQUANTUM = N'. Maybe I didn't understand you, but, > > SCULL_IOCTQUANTUM is not a call (neither a macro); it's only a single > > value that is assinged to a functionality in the ioctl system call for > > the scull module. > > > > So, when a user-space application ioctls the device: > > > > #include <scull.h> > > ioctl (dev, SCULL_IOCTQUANTUM, some_number); > > > > it's done: > > scull_quantum = some_number > > > > > > > > > And wht is the use of capable (CAP_SYS_ADMIN)? > > > > It's a better way to manipulate permissions by the linux. Imagine a > > case where users must have read/write access to device, but they > > mustn't change control parameters of a device. Read the section > > "Capabilities and Restricted Operations", page 144 ldd 3rd edition. > > > > Regards, > > Riba > > > > -- > > Kernelnewbies: Help each other learn about the Linux kernel. > > Archive: http://mail.nl.linux.org/kernelnewbies/ > > FAQ: http://kernelnewbies.org/faq/ > > > > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
