hi , Thank you for your reply, can i ask some more question?
Inside the system call , the kernel often copy the data by calling copy_from_user() rather than just using strcpy(), is it because the memory mapping in kenel space is different from user space? for example , now user program want to pass a pointer *a to kernel space , is it true that *a seems means address 0xb000 to user space but actually it is at 0xc000 at kernel space?
Thx a lot, TOM
Jan-Benedict Glaw wrote:
On Wed, 2005-04-13 12:21:41 +0800, Tomko <[EMAIL PROTECTED]>
wrote in message <[EMAIL PROTECTED]>:
While i am reading the source code of the linux system call , i find that the system call need to call copy_from_user() to copy the data from user space to kernel space before using it . Why not use it directly as the system call has got the address ? Furthermore , how to distinguish between user space and kernel space ?
Think about the memory access. The page that contains the data could be swapped out, so the kernel isn't allowed to just access it, because it's not there.
MfG, JBG
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