lkml.org 
[lkml]   [2005]   [Apr]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Why system call need to copy the date from the userspace before using it
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 <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
>
>
>

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-04-13 12:48    [W:0.043 / U:2.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site