Re: Why system call need to copy the date from the userspace before using it

Jan-Benedict Glaw
2005-04-13T10:30:53Z

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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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