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Subject: Re: [virtio-comment] Block Device VIRTIO_BLK_F_RO clarification needed.
On Mon, Jan 20, 2020 at 11:45:05AM +0000, Damir Shaikhutdinov wrote: > Hello! > > While reading section 5.2 of the spec, I found that VIRTIO_BLK_F_RO feature could use > some additional clarification regarding handling requests when it was offered. > > This RO feature is described as "Device is read only" (Section 5.2.3). There are some explicit requirements for this feature, but they only describe a "write request". > > 5.2.5 p3 says "If the VIRTIO_BLK_F_RO feature is set by the device, any write requests will fail." > > 5.2.6 says "The type of the request is either a read (VIRTIO_BLK_T_IN), a write (VIRTIO_BLK_T_OUT) ...", so "write request" mentioned in 5.2.5 p3 is VIRTIO_BLK_T_OUT. > > 5.2.6.2 says "A device MUST set the status byte to VIRTIO_BLK_S_IOERR for a write request if the VIRTIO_BLK_F_RO > feature if offered, and MUST NOT write any data." > > What is missing here is a requirement for features and other types of requests in case of VIRTIO_BLK_F_RO: > > * config.writeback field (guarded by VIRTIO_BLK_F_CONFIG_WCE feature) > * VIRTIO_BLK_T_ FLUSH (guarded by VIRTIO_BLK_F_FLUSH feature) > * VIRTIO_BLK_T_DISCARD (guarded by VIRTIO_BLK_F_DISCARD feature) > * VIRTIO_BLK_T_WRITE_ZEROES (guarded by VIRTIO_BLK_F_WRITE_ZEROES feature) > > Configuration field, requests and features described above make no sense in presence of VIRTIO_BLK_F_RO. > > This can be clarified in several ways, for example: > > 1. Device should not offer CONFIG_WCE, FLUSH, DISCARD and WRITE_ZEROES features if it offers RO feature (partially contradicts 5.2.5.2 "Device SHOULD always offer VIRTIO_BLK_F_FLUSH") > 2. Device must set the status byte to IOERR for FLUSH, DISCARD and WRITE_ZEROES requests if it offers RO feature. > > > What do you think about that? I guess flush can even be allowed, it's harmless if nothing is written, right? I agree DISCARD and WRITE_ZEROES must fail. And set VIRTIO_BLK_S_IOERR I guess? It's too late to disallow configurations such as a combination of VIRTIO_BLK_F_CONFIG_WCE and VIRTIO_BLK_F_RO, devices out there might be setting this combination. > With best regards, > Damir Shaikhutdinov > > Please mind our privacy notice<https://www.opensynergy.com/datenschutzerklaerung/privacy-notice-for-business-partners-pursuant-to-article-13-of-the-general-data-protection-regulation-gdpr/> pursuant to Art. 13 GDPR. // Unsere Hinweise zum Datenschutz gem. Art. 13 DSGVO finden Sie hier.<https://www.opensynergy.com/de/datenschutzerklaerung/datenschutzhinweise-fuer-geschaeftspartner-gem-art-13-dsgvo/> > > This publicly archived list offers a means to provide input to the > OASIS Virtual I/O Device (VIRTIO) TC. > > In order to verify user consent to the Feedback License terms and > to minimize spam in the list archive, subscription is required > before posting. > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > List help: virtio-comment-help@lists.oasis-open.org > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > Committee: https://www.oasis-open.org/committees/virtio/ > Join OASIS: https://www.oasis-open.org/join/
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