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

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Subject: [Xen-devel] block ring interface: nr_segments = 0 results in BLKIF_RSP_ERROR
From: Chris Youb <chris_youb@xxxxxxxx>
Date: Thu, 24 Aug 2006 16:41:36 -0400 (EDT)
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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:
     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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