I could able derefence and used the char buffer passed from user program to the kernel module.
in kernel module i could able derefrence and used this buffer without using copy_from_user()
function. why is this function required or any guidelines to use this function.
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>>>> But I coud able to read the user space buffer without using copy_from_user() function ?
in the kernel module.
There are many ways (netlinks sockets, signals ...) of comunication between user and kernel space, but using a relaible way is more important.
>>> what problems are created when i am directly using the userspace buffer without
calling copy_from_user() function
Well, its possible that the user space process is blocked and the corrosponding pages pertaining to the userspace process are swapped out. Therefore, this would end up in a kernel panic / kernel segfault, as this could cause a page fault when a page is swapped out. However, this is preveneted if you make use copy_from/to_user().
Hope this helps!!!
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by: askbPosted on 2009-10-30 at 05:46:42ID: 25702351
>>> why is this function required or any guidelines to use this function.
copy_to_user() and copy_from_user() are basic methods to transfer of data between kernel space and users space.
For writing into user-space, the method copy_to_user() is provided. It takes three parameters. The first is the destination memory address in the process's address space. The second is the source pointer in kernel-space. Finally, the third argument is the size in bytes of the data to copy.
For reading from user-space, the method copy_from_user() is analogous to copy_to_user(). The function reads from the second parameter into the first parameter the number of bytes specified in the third parameter.
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