Re: [RFC] Netlink and user-space buffer pointers

[Andrew Vasquez]

On Thu, 20 Apr 2006, James Smart wrote:

> Note: We've transitioned off topic. If what this means is "there isn't a 
> good
> way except by ioctls (which still isn't easily portable) or system calls",
> then that's ok. Then at least we know the limits and can look at other
> implementation alternatives.

this topic has been brought-up many times in the past, most recently:

	http://thread.gmane.org/gmane.linux.drivers.openib/19525/focus=19525
	http://thread.gmane.org/gmane.linux.kernel/387375/focus=387455

where is was suggested to pathscale folks to use some blend of sysfs,
netlink sockets and debugfs:

	http://kerneltrap.org/node/4394

> >>Mike Christie wrote:
> >Instead of netlink for scsi commands and transport requests....
> >
> >For scsi commands could we just use sg io, or is there something special
> >about the command you want to send? If you can use sg io for scsi
> >commands, maybe for transport level requests (in my example iscsi pdu)
> >we could modify something like sg/bsg/block layer scsi_ioctl.c to send
> >down transport requests to the classes and encapsulate them in some new
> >struct transport_requests or use the existing struct request but do that
> >thing people keep taling about using the request/request_queue for
> >message passing.
> 
> Well - there's 2 parts to this answer:
> 
> First : IOCTL's are considered dangerous/bad practice and therefore it would
>   be nice to find a replacement mechanism that eliminates them. If that
>   mechanism has some of the cool features that netlink does, even better.
>   Using sg io, in the manner you indicate, wouldn't remove the ioctl use.
>   Note: I have OEMs/users that are very confused about the community's 
>   statement
>   about ioctls. They've heard they are bad, should never be allowed, will no
>   be longer supported, but yet they are at the heart of DM and sg io and 
>   other
>   subsystems. Other than a "grandfathered" explanation, they don't 
>   understand
>   why the rules bend for one piece of code but not for another. To them, all
>   the features are just as critical regardless of whose providing them.

I believe it to be the same for most hardware-vendor's customers...

> Second: transport level i/o could be done like you suggest, and we've
>   prototyped some of this as well. However, there's something very wrong
>   about putting "block device" wrappers and settings around something that
>   is not a block device.

Eeww...  no wrappers.  Your netlink prototypes certainly get FC-
transport further along, but would also be nice if there could be some
subsystem consensus on *the* interface.

I honestly don't know which interface is *best*, but from a HBA
vendors perspective managing per-request locally allocated memory is
undesirable.

Thanks,
av
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