Re: sizeof(ptr) or sizeof(*ptr)?

[Matthew Dharm <mdharm-kernel@one-eyed-alien.net>]

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On Sun, Feb 27, 2005 at 08:25:04PM +0000, pmarques@grupopie.com wrote:
> I decided to tweak sparse to give warnings on sizeof(pointer), so that I could
> check for other cases like this. The tweak was a very crude hack that I'm not
> proud of, and I am still trying to make it more reliable.
> 
> So far I found 2 interesting cases (in 2.6.11-rc5). I'm not sure they are bugs,
> but they sure look suspicious.
> 
> 1: drivers/usb/storage/usb.c:788
> 
> 	/*
> 	 * Since this is a new device, we need to register a SCSI
> 	 * host definition with the higher SCSI layers.
> 	 */
> 	us->host = scsi_host_alloc(&usb_stor_host_template, sizeof(us));
> 	if (!us->host) {
> 		printk(KERN_WARNING USB_STORAGE
> 			"Unable to allocate the scsi host\n");
> 		return -EBUSY;
> 	}
> 
> "us" is a "struct us_data *". It seems pretty weird that we're allocating
> something the size of a pointer, and then waste a pointer to keep the address
> where it is allocated. So maybe this should be:
> 
> 	us->host = scsi_host_alloc(&usb_stor_host_template, sizeof(*us));

This is actually correct as-is.  We're allocating a host, and asking for
the sizeof(pointer) in the 'extra storage' section.  We then store the
pointer (not what it points to) in the extra storage section a few lines down.

Matt

-- 
Matthew Dharm                              Home: mdharm-usb@one-eyed-alien.net 
Maintainer, Linux USB Mass Storage Driver

S:  Another stupid question?
G:  There's no such thing as a stupid question, only stupid people.
					-- Stef and Greg
User Friendly, 7/15/1998

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