Re: sg driver and Fedora Core 2

[Jeff Garzik <jgarzik@pobox.com>]

Alan Cox wrote:
> On Sat, May 29, 2004 at 01:27:58PM -0400, Jeff Garzik wrote:
> 
>>Really what needs to happen is a generic userland tap attaches to a 
>>chrdev, issues an ioctl(2) to attach to a request_queue, and then does 
>>read(2)/write(2)/mmap(2) to communicate with the request_queue.
> 
> 
> Is there a reason that couldn't be part of the block layer sysfs in 2.7.x 
> 
> 
>>:)
>>Call it /dev/bsg, or somesuch.
> 
> 
> Except that I wonder if it should be in sysfs I agree entirely. 

I'll let others haggle over the device name and location <grin>  sysfs 
or whereever is fine with me.  I just care about the chrdev's behavior :)


>>  OTOH, the SG_IO ioctl does eliminate the userland app needing to 
>>worry about _any_ target/addressing information, since that is implicit 
>>in the dentry pointing to the blkdev's inode.
> 
> 
> It makes it very hard to scan scsi busses, which is what the flash burner
> app does, and what xsane does (although sane survives ok because there
> are no kernel scanner device drivers)


This is precisely the problem with the only-SG_IO approach as well:

AFAICS, you lose the ability to scan the bus, just as you gain the 
ability to not have to care about scanning the bus.  Getting back on 
topic, I agree with you that the Fedora change [if it is as you 
describe] is not a good one.  And breakage in a stable kernel version is 
also quite annoying.

	Jeff