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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