On Mon, Oct 11, 2004 at 14:22:56 +0530, Pavan Kumar wrote: > copy_to_user/copy_from_user takes care of address not in memory (page Yes. Note: That means, that copy_to/from_user MAY SLEEP and thus must not be called with spinlocks held. > fault), For x86 atleast u can do blind memcpy ( it not > recommended/portable though ). On i386, copy_to/from_user uses the FS register. You definitely can't access kernel memory with that segment, but it's likely that you can address user-space with kernel segment. Anyway, you can't do blind memcpy because you can't be sure it's mapped, if nothing else. > Pl. correct me if i am wrong. > > On Mon, 11 Oct 2004 09:41:30 +0200, Jan Hudec <bulb@xxxxxx> wrote: > > On Mon, Oct 11, 2004 at 09:55:37 +0530, mohanlal jangir wrote: > > > I have a character device and some of its functions are being called by > > > ioctl. In a function, I do copy_to_user and copy_from_user to get the user > > > space data in kernel memory. My question is, if this function doesn't sleep, > > > can I avoid calls to copy_to_user and copy_from_user? > > > > No, you can't. The user-space memory is not directly addressable from > > kernel. > > > > ------------------------------------------------------------------------------- > > Jan 'Bulb' Hudec <bulb@xxxxxx> > > > > > > > ------------------------------------------------------------------------------- Jan 'Bulb' Hudec <bulb@xxxxxx>
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