On Fri, Apr 21, 2006 at 06:11:47PM +0000, Talib Alim wrote: > >On Thu, Apr 20, 2006 at 10:42:16PM +0000, Talib Alim wrote: > >> > If I'm reading Talib's question correctly, it looks like he is > >> >treating the pointer as opaque in user space, i.e. not directly > >> >referencing the memory in user space, but he is passing the pointer back > >> >to his kernel module at some point in the future, and he wants to make > >> >sure that on this subsequent call the pointer is still valid. Without > >> >seeing his code and knowing exactly what he is trying to accomplish, I > >> >can't say for sure. Whatever the case, for saving opaque kernel > >> >pointers I would use the private_data field in the file structure, > >> >assuming this is a driver or virtual file system he is working with. > >> > > >> >Bob > >> > >> Bob, you are correct. > >> > >> When using application wants service from my device, it open character special file and get a descriptor. Now through ioctl it can make hundreds of request to my > >> device. > >> > >> Driver (i.e. my code) allocate memory for each request (through slab cache). There could be many transections for each request. (think if you open a for file you > >> can do read, write operations). > >> > >> And all I want to make sure that application (by mistake or by choice) is not passing a junk value to my code. Once, I verify that memory is OK, than I can look > >for > >> signatures to make sure that it is pointing to correct data structure. > >> > >> Talib > > > > I really don't understand what you are trying to do :) > > You want to pass the kernel pointer to the userspace application and > > then pass back the kernel pointer from the user application to the > > kernel ?? > > > > You can't do any operation from the user space on the kernel pointer, > > so why do you want to pass it to the user space application ? > > So that next time user calls my driver for service, it can identify context of request (like fd in read) Ok, I see. What you have to do is to maintain a cursor inside the driver. You init the cursor to 0 (when device is opened). You next adds the number of bytes read (at each read operation). You move the cursor with the seek function. But don't do what you said. -- tyler tyler@xxxxxxxx ___________________________________________________________________________ Faites de Yahoo! votre page d'accueil sur le web pour retrouver directement vos services préférés : vérifiez vos nouveaux mails, lancez vos recherches et suivez l'actualité en temps réel. Rendez-vous sur http://fr.yahoo.com/set -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
