Re: cross-bounday memory communication b/w user app and the Kernel.How?
Re: cross-bounday memory communication b/w user app and the Kernel.How?
- Subject: Re: cross-bounday memory communication b/w user app and the Kernel.How?
- From: Michael Smith <email@hidden>
- Date: Thu, 1 Jun 2006 23:15:59 -0700
On Jun 1, 2006, at 9:06 PM, rohit dhamija wrote:
Thanks a lot for your comments !! Your suggestions are very good
and valuable.
B/w i have one query ,
Create the IOMemoryDescriptors directly against the user-space
addresses and do your I/O with those.
At this point i have memory of type IOMemoryDescriptor*. But Now I
need to copy some information in this memory. So is it fine to copy
using memcopy :to copy information in descr (of type
IOMemoryDescriptor* ) ??
There is nothing to copy.
like
IOMemoryDescriptor * outDescriptor = NULL;
// Get the data into kernel space
outDescriptor = IOMemoryDescriptor::withAddress(
(vm_address_t)pComm->command_payload,
sizeof(command_structure),
kIODirectionOut,
fClientTask);
now I need to copy some data into
so is it fine to do:
memcpy((void*)&outDescriptor, mydataBuffer, sizeof(MYDATABUFFER));
IF not, then how to copy/fill info in the descriptor ?
You don't. The descriptor refers to the buffer that already exists
in the user-space process' address space. You don't need to copy
anything.
I want to ask "don't they teach you anything in school these days?"
but perhaps that's a bit harsh. I would suggest that if you plan on
doing much more work on device drivers that you should spend a little
time reading up on the history and design of operating systems.
There are a lot of fundamental things that it would really help you
to know.
Might I suggest:
http://www.osxbook.com/
http://www.amazon.com/gp/product/0201549794/qid=1149228811/sr=1-7/
ref=sr_1_7/104-5530617-5549562?s=books&v=glance&n=283155
http://www.amazon.com/gp/product/0130313580/sr=8-1/qid=1149228772/
ref=pd_bbs_1/104-5530617-5549562?_encoding=UTF8
http://www.amazon.com/gp/product/0131429388/qid=1149228811/sr=1-6/
ref=sr_1_6/104-5530617-5549562?s=books&v=glance&n=283155
http://www.amazon.com/gp/product/0130981389/qid=1149228870/sr=2-1/
ref=pd_bbs_b_2_1/104-5530617-5549562?s=books&v=glance&n=283155
http://www.amazon.com/gp/product/013021034X/qid=1149228906/sr=1-2/
ref=sr_1_2/104-5530617-5549562?s=books&v=glance&n=283155
I'm sure that you can get these books for considerably less
elsewhere, it was just convenient to use Amazon to look them up. I'm
also sure that other folks on this list will have their own
suggestions; the above clearly shows my *nix background.
= Mike
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