Hi mohit, On Sun, Sep 26, 2010 at 7:38 AM, mohit verma <mohit89mlnc@xxxxxxxxx> wrote: > guysssss, > > will u please highlight some corner points of copy_to/from_user program (the > motive of this thread )? What I recall from copy_to/from_user when I looked at how it was implemented on the ARM several years ago (and this might have been with the 2.4 version of the kernel - I don't recall), is that it registers with the linux exception framework (which is non-trivial IIRC) so that if it tries to access a region of memory which isn't mapped then it causes a special type of exception rather than a normal pagefault. It also deals with the different address spaces. On the ARM, it turns out that nothing really special is required. You can use memcpy and get the same results as copy_to/from_user when the pointers and sizes are valid. However, if an invalid pointer gets passed to memcpy, it will cause a fault, whereas copy_to/from_user intercepts the fault with the exception handler -- Dave Hylands Shuswap, BC, Canada http://www.DaveHylands.com/ -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
