Messages in this thread | | | Date | Wed, 13 Apr 2005 12:29:16 +0200 | From | Jan-Benedict Glaw <> | Subject | Re: Why system call need to copy the date from the userspace before using it |
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On Wed, 2005-04-13 12:21:41 +0800, Tomko <tomko@haha.com> wrote in message <425C9E55.6010607@haha.com>: > 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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