[Xen-devel] block ring interface: nr_segments = 0 results in BLKIF_RSP_ERROR

[Chris Youb <chris_youb@xxxxxxxx>]

I am currently developing a blkfront.c for a custom OS over Xen 3.0.2-2.  Typical I/O is working, however, I ran into an error while testing a corner case.

 

On standard I/O, where  { 1 <= nr_segments < BLKIF_MAX_SEGMENTS_PER_REQUEST } blkif_int()'s bret->status returns BLKIF_RSP_OKAY.

 

Yet when { nr_segments == 0 } blkif_int's bret->status is non-zero. (Yes I realize this is an I/O call of zero-length.)

 

I checked the documentation and section "8.2.2 Block ring interface" states the following but doesn't exclude 0:

 

"nr_segments

     number of segments for scatter / gather IO described by this request"

 

1) Is it possible there is a problem w/ my front-end driver (ie does anyone else see this behaviour)?

 

2) If this is back-end related, shouldn't it just return BLKIF_RSP_OKAY?

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