[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] blkif: add indirect descriptors interface to public headers
> -----Original Message----- > From: Ian Campbell > Sent: 12 November 2013 14:29 > To: Konrad Rzeszutek Wilk > Cc: Paul Durrant; xen-devel@xxxxxxxxxxxxxxxxxxxx; Keir (Xen.org); Jan Beulich; > Roger Pau Monne > Subject: Re: [Xen-devel] [PATCH] blkif: add indirect descriptors interface to > public headers > > On Tue, 2013-11-12 at 09:22 -0500, Konrad Rzeszutek Wilk wrote: > > > > > +struct blkif_request_indirect { > > > > + uint8_t operation; /* BLKIF_OP_INDIRECT > > > > */ > > > > + uint8_t indirect_op; /* BLKIF_OP_{READ/WRITE} > > > > */ > > > > + uint16_t nr_segments; /* number of segments > > > > */ > > > > > > This is going to be a problem. What alignment boundary are you > > expecting the next field to start on? AFAIK 32-bit gcc will 4-byte > > align it, 32-bit MSVC will 8-byte align it. > > > > > > > Oh no. I thought that the Linux one had this set correctly, ah it did: > > > > > > struct blkif_request_indirect { > > [...] > > } __attribute__((__packed__)); > > That attribute packed isn't allowed in the public interface headers. > > Since compilers do differ in their packing, and guests may be using > various pragmas, it might be useful to write down that for x86 these > headers are to be treated as using the <WHATEVER> ABI (gcc? Some Intel > standard?). > Can we go for types aligned on their size then rather than gcc brokenness. Paul > For ARM we reference the specific standard[0]. It is up to the guest OS > to make sure that it's version of the headers lay things out following > that standard (NB Linux blkif.h is currently buggy on ARM in this > regard, Julien has the details). > > Ian. > > [0] > http://xenbits.xen.org/docs/unstable/hypercall/arm/include,public,arch- > arm.h.html#incontents_arm_abi _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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