Re: [Xen-devel] [PATCH RFC 2/5] blkif: document new blkback path xenstore node

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jun 02, 2015 at 05:22:04PM +0200, Roger Pau Monné wrote:
> El 01/06/15 a les 15.24, Wei Liu ha escrit:
> > On Fri, May 22, 2015 at 11:18:55AM +0200, Roger Pau Monne wrote:
> >> FreeBSD blkback uses the path xenstore node in order to fetch the path to
> >> the underlying backing storage (either a block device or raw image). This
> >> node is set by the hotplug scripts.
> >>
> >> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >> Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> >> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> >> Cc: Tim Deegan <tim@xxxxxxx>
> >> ---
> >>  xen/include/public/io/blkif.h | 12 ++++++++++--
> >>  1 file changed, 10 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/xen/include/public/io/blkif.h b/xen/include/public/io/blkif.h
> >> index 6baf7fb..b1e2245 100644
> >> --- a/xen/include/public/io/blkif.h
> >> +++ b/xen/include/public/io/blkif.h
> >> @@ -89,8 +89,15 @@
> >>   *      Values:         string
> >>   *
> >>   *      A free formatted string providing sufficient information for the
> >> - *      backend driver to open the backing device.  (e.g. the path to the
> >> - *      file or block device representing the backing store.)
> >> + *      hotplug script to attach the device and provide a suitable
> >> + *      handler (ie: a block device) for blkback to use.
> >> + *
> >> + * path
> >> + *      Values:         string
> >> + *      Notes: 11
> >> + *
> >> + *      A free formatted string that contains the path to the backing 
> >> device
> >> + *      for this blkback instance.
> > 
> > Why can't FreeBSD use the same "physical-device" node as Linux and
> > NetBSD do? AIUI from reading this doc "physical-device" node already
> > covers both "file" and "block device", i.e. it's a superset of the
> > proposed "path" node here.
> 
> Not sure why, but "physical-device" is not documented at all in blkif.h.
> 

Er...

> I don't mind using the "physical-device" node, it's just that both Linux
> and NetBSD use it to store the block device major and minor numbers, and
> FreeBSD instead needs to store an absolute path (to either a block or
> regular file). If people think it's fine to have different formats for
> "physical-device" depending on the underlying OS I don't mind using it
> on FreeBSD also.
> 

I think you can just document it and claim it your own pet node. :-)

I don't have much say in this field. I'm fine with anything that's
clearly documented.

Wei.

> Roger.

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