scsi_debug: dev_size_mb <= 0 fix

Hi,

While working on getting 10000 scsi_debug disks working simultaneously, I came across a problem with the driver. According to the webpage,

``All simulated dummy devices share the same RAM. If a value of 0 or less is given then dev_size_mb is forced to 1 so 1 MB of RAM is used.''

However, when I sent in dev_size_mb=0, the module would return an "Out of memory" error. I discovered that there was no check for a zero/negative value for dev_size_mb and thus a vmalloc(0) resulted, which apparently results in a NULL pointer and the driver thinks there is no memory available.

I believe the patch below fixes this.

Applys-to: 2.6.7

Description: Adds check for non-positive value of scsi_debug_dev_size_mb, as per the description on the scsi_debug web page. If the parameter is given as 0 or less, then the size of the reserved RAM is defaulted to 1MB. Compile-tested and run-tested.

@@ -1491,6 +1491,10 @@ static int __init scsi_debug_init(void)
 	int host_to_add;
 	int k;
 
+	/* if dev_size_mb is passed as <= 0, then it is forced to 1. */
+	if (scsi_debug_dev_size_mb <= 0)
+		scsi_debug_dev_size_mb = 1;
+
 	sdebug_store_size = (unsigned long)scsi_debug_dev_size_mb * 1048576;
 	sdebug_capacity = sdebug_store_size / SECT_SIZE;