From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fam Zheng Subject: Re: [PATCH 2/2] virtio_scsi: Implement fc_host Date: Tue, 17 Jan 2017 22:05:00 +0800 Message-ID: <20170117140500.GA19638@lemon> References: <20170116160430.11815-1-famz@redhat.com> <20170116160430.11815-3-famz@redhat.com> <95f96b48-aa75-0094-a634-db9c13035336@redhat.com> <20170116172656.GB11780@lemon> <4049e6cf-b398-4ebd-3248-77c333e65331@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <4049e6cf-b398-4ebd-3248-77c333e65331@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Paolo Bonzini Cc: "James E.J. Bottomley" , linux-scsi@vger.kernel.org, "Martin K. Petersen" , "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, stefanha@redhat.com List-Id: virtualization@lists.linuxfoundation.org On Tue, 01/17 14:17, Paolo Bonzini wrote: > > > On 16/01/2017 18:26, Fam Zheng wrote: > >> Is the endianness correct for big-endian host here? > > > > I think so. The fc_host sysfs uses u64 to represent port_name and node_name, > > this patch does the same, so using virtio_* helpers for these fields should > > handle the endianness correctly. > > I was suspicious about it because they are defined as "u8 x[8]" in the > virtio_scsi_config struct. So you would need to read with > virtio_cread_bytes and pass the result to wwn_to_u64. > > For example, if you have 0x500123456789abcd this would be > > 0x50 0x01 0x23 0x45 0x67 0x89 0xab 0cd > > in virtio_scsi_config, and then virtio_cread64 would read it as a > little-endian u64, 0xcdab896745230150. Maybe your QEMU patch is also > writing things as little-endian 64-bit integers, rather than 8-element > arrays of bytes? Yes, they all used 64-bit integers in a "less surprising" endian. I think there is an endianness conecpt to WWN, as in 0x500123456789abcd; and there is an native endianness to virtio, which is little-endian. If we use a "u8 x[8]" type in the spec and want the WWN's MSB, namely the 0x50 stuff, to be the first byte, is it worth to explicitly document that to avoid confusion? Fam