FYI - netlink (and sysfs, and I believe debugfs) do not exist with
vmware drivers... Additionally, with netlink, many of the distros no
longer include libnl by default in their install images. Even
interfaces that you think exist on vmware, may have very different
semantical behavior (almost all of the transport stuff either doesn't
exist or is only partially implemented).
One big caveat I'd give you: It's not so much the interface being used,
but rather, what are you doing over the interface. One of the goals of
the community is to present a consistent management paradigm for like
things. Thus, if what you are doing is generic, you should do it in a
generic manner so that all drivers for like hardware can utilize it.
This was the motivation for the protocol transports. Interestingly, even
the transports use different interfaces for different things. It all
depends on what it is.
Lastly, some things are considered bad practice from a kernel safety
point of view. Example: driver-specific ioctls passing around user-space
buffer pointers. In these cases, it doesn't matter what interface you
pick, they'll be rejected.
-- james s
Mukker, Atul wrote:
Thanks Brian. Netlink seems to be appropriate for our purpose as well, almost too good :-)
That make me think, what's the catch? The SCSI drivers are not heavy usage of this interface for one.
Are the other caveats associated with it?
Best regards,
Atul Mukker
-----Original Message-----
From: Brian King [mailto:brking@xxxxxxxxxxxxxxxxxx]
Sent: Friday, July 17, 2009 11:36 AM
To: Mukker, Atul
Cc: linux-scsi@xxxxxxxxxxxxxxx
Subject: Re: Recommended HBA management interfaces
Mukker, Atul wrote:
Hi All,
We would like expert comments on the following questions regarding
management of HBA from applications.
Traditionally, our drivers create a character device node, whose
file_operations are then used by the management applications to
transfer HBA specific commands. In addition to being quirky, this
interface has a few limitations which we would like to remove, most
important being able to seamlessly handle asynchronous events with
data transfer.
1. What is (are) the other standard/recommended interfaces which
applications can use to transfer HBA specific commands and data.
Depends on what the commands look like. With ipr, the commands that
the management application need to send to the HBA look sufficiently
like SCSI that I was able to report an sg device node for the adapter
and use SG_IO to send these commands.
sysfs, debugfs, and configfs are options as well.
2. How should an LLD implement interfaces to transmit asynchronous
information to the management applications? The requirement is to be
able to transmit data buffer as well as notifications for events.
I've had good success with netlink. In my use I only send a notification
to userspace and let the application send some commands to figure out
what happened, but netlink does allow to send data as well. It makes it
very
easy to have multiple concurrent readers of the data, which I've found
very
useful.
3. The interface should be able to work even if no SCSI devices are
exported to the kernel.
netlink allows this.
4. Should work seamlessly across vmware and xen kernels.
netlink should work here too.
-Brian
--
Brian King
Linux on Power Virtualization
IBM Linux Technology Center
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