site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=L+xkKeRCAGzMkSQzPRzaIMpy2hXiK9Qb8BeYA9MDGTKOSmmYXaTSJxZFzSjRRQdkVD4ObhTKj1Ek6DKroEgSGEW5TPEuudlShnhIuVeuAQBEYT09aNHkOog0j/ROJ9I2C1A4/V9Wcgqm/llaLBu/9ZUrwBUI0PHVGf6jvIZe6ho= Hi Michael, I shall try to explain my doubt again: I need to send various command packets to the device and get the corresponding response packet. My command consists of [a]. command identifier i.e. command_id [b] command payload: This command payload differs from command to command. The maximum size of command payload is: "unsigned char Commandpayload[257];" My output response packet again varies from command to command. The maximum size of response packet can be "unsigned char ResponseData[256];" So, one way is to make the shared structure (the structure to communicate with user kernel space) can be: typedef struct _mypacket{ int command_id; union { unsigned char Commandpayload[257]; unsigned char ResponseData[256] } MY_PACKET, *PMY_PACKET; But this type of structure will consume the maximum memory. So In order to avoid it, can we have pointers instead of static memory allocation ? The command packet the structure will be struct command_packet{ int command_id unsigned char* cmd_payload; int size_of_command; } Similary for response_packet. Is this possible ? Rohit On Jun 2, 2006, at 12:28 AM, rohit dhamija wrote:

Thanks for your suggestion, but i need to tell you two things :

1. I am sure that you did not get my question right. That's entirely possible. Regarding my query,

...

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 know that the descriptor refers to the buffer only. But say for example I wish to set this data to all zero's. I'm not sure why you would want to do this. If you want a buffer full of zeroes, you would create an IOBufferMemoryDescriptor, since that will have private memory associated with it, already mapped into your address space. In your example, you want to send the command buffer that the user has supplied, so you need a descriptor that refers to it. So in this case: (a) will I give address of the structure OR (b) address of IOMemoryDescriptor,, as the first parameter to memset ? Neither. The IOMemoryDescriptor is a class instance, and the structure pointer in your example just points to a couple of pointers. You can't use the pointers inside the structure, because they are not valid in your address space. Why do you want to change the contents of the command buffer? In the typical interface model, the caller is not going to expect you to do anything to it. Mapping it so that you can write into it will be expensive, too. Similarly what if I want to copy the data AGAIN in my driver side ? Do I need to send the address of structure to the memcpy ? Or do i need to pass address of IOMemoryDescriptor as the first parameter to memcpy. You don't want to copy the data at all, unless you are going to modify it before you send it out. I hope I am able to clarify my query. Please comment. Not really. I don't yet understand why you are obsessed with copying this data... = Mike

-- Rohit Dhamija(M) 9818446545 _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... On 6/2/06, Michael Smith <drivers@mu.org> wrote: This email sent to site_archiver@lists.apple.com