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SubjectRe: RFC: ipath ioctls and their replacements
On Wed, Jan 18, 2006 at 04:43:31PM -0800, Bryan O'Sullivan wrote:
> Opening the /dev/ipath special file assigns an appropriate free
> unit (chip) and port (context on a chip) to a user process.

Shouldn't you just open the proper chip device and port device itself?
That drops one ioctl.

> Think of it as similar to /dev/ptmx for ttys, except there isn't
> a devpts-like filesystem behind it. Once a process has
> opened /dev/ipath, it needs to find out which unit and port it
> has opened, so that it can access other attributes in /sys. To
> do this, we provide a GETPORT ioctl.

> USERINIT and BASEINFO work with mmap to set up direct access to
> the hardware for user processes. We intend to turn these into a
> single ioctl, USERINIT. This copies a substantial amount of
> information to and from userspace.

Why not just use mmap? What's the special needs?

> RCVCTRL enables/disables receipt of packets.

sysfs file.

> SET_PKEY sets a partition key, essentially telling hardware
> which packets are interesting to userspace.

sysfs file.

> UPDM_TID and FREE_TID are used for RDMA context management.

sysfs files.

> WAIT waits for incoming packets, and can clearly be replaced by
> file_ops->poll.

Use poll.

> GETCOUNTERS, GETUNITCOUNTERS and GETSTATS can all be replaced by
> files in sysfs.

good.

> For subnet management:
>
> GETLID, SET_LID, SET_MTU, SET_GUID, SET_MLID, GET_MLID,
> GET_DEVSTATUS, GET_PORTINFO and GET_NODEINFO can all be replaced
> by files in sysfs.
>
> SET_LINKSTATE changes the link state.
>
> SEND_SMA_PKT and RCV_SMA_PKT send and receive subnet management
> packets. I *think* they could be replaced by read and write
> methods on a new special file, although the semantics aren't a
> super-clean match.

Use netlink for subnet stuff.

> For diagnostics:
>
> DIAGENTER and DIAGLEAVE put the driver into and out of diag
> mode. These could be replaced by open/close of a special file.

Use debugfs.

> DIAGREAD and DIAGWRITE perform direct accesses to the device's
> PCI memory space. I think these could be replaced by read and
> write, but they are again subject to the make-coworker-barf
> problem.

Use debugfs.

> HTREAD and HTREAD perform direct accesses to the device's PCI
> config space. Same disagreement problem as DIAGREAD and
> DIAGWRITE.

Use the pci sysfs config files, don't duplicate existing functionality.

> SEND_DIAG_PKT can be replaced with whatever sends and receives
> subnet management packets, as above.

netlink or debugfs.

Hope this helps,

greg k-h
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