Mike Christie wrote:
For the tasks you want to do for the fc class is performance critical?
No, it should not be.
If not, you could do what the iscsi class (for the netdev people this is
drivers/scsi/scsi_transport_iscsi.c) does and just suffer a couple
copies. For iscsi we do this in userspace to send down a login pdu:
/*
* xmitbuf is a buffer that is large enough for the iscsi_event,
* iscsi pdu (hdr_size) and iscsi pdu data (data_size)
*/
Well, the real difference is that the payload of the "message" is actually
the payload of the SCSI command or ELS/CT Request. Thus, the payload may
range in size from a few hundred bytes to several kbytes (> 1 page) to
Mbyte's in size. Rather than buffer all of this, and push it over the socket,
thus the extra copies - it would best to have the LLDD simply DMA the
payload like on a typical SCSI command. Additionally, there will be
response data that can be several kbytes in length.
... I think there may be issues with packing structs or 32 bit
userspace and 64 bit kernels and other fun things like this so the iscsi
pdu and iscsi event have to be defined correctly and I guess we are back
to some of the problems with ioctls :(
Agreed. In this use of netlink, there's not a lot of wins for netlink over
ioctls. It all comes down to 2 things: a) proper portable message definition;
and b) what do you do with that non-portable user space buffer pointer ?
-- james s
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