This field is only valid when the VIRTIO_BLK_F_BLK_SIZE feature bit is offered by the device. The blk_size field actually represents the logical block size of the device. It is always a power of two and typically ranges from 512 bytes to larger values such as 4 KB. Add description for this field to provide clarity on its constraints. Fixes: https://github.com/oasis-tcs/virtio-spec/issues/208 Reviewed-by: Daniel Verkamp <dverkamp@xxxxxxxxxxxx> Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx> Signed-off-by: Max Gurtovoy <mgurtovoy@xxxxxxxxxx> --- changes from v4: - reorder paragraphs (MST, Matias) --- device-types/blk/description.tex | 33 ++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/device-types/blk/description.tex b/device-types/blk/description.tex index 2712ada..093a139 100644 --- a/device-types/blk/description.tex +++ b/device-types/blk/description.tex @@ -135,6 +135,10 @@ \subsection{Device configuration layout}\label{sec:Device Types / Block Device / present. The availability of the others all depend on various feature bits as indicated above. +The field \field{blk_size} reports the block size of the device, expressed in +bytes. This field exists only if VIRTIO_BLK_F_BLK_SIZE is offered by the +device. + The field \field{num_queues} only exists if VIRTIO_BLK_F_MQ is set. This field specifies the number of queues. @@ -282,6 +286,13 @@ \subsection{Device Initialization}\label{sec:Device Types / Block Device / Devic \drivernormative{\subsubsection}{Device Initialization}{Device Types / Block Device / Device Initialization} +Drivers SHOULD negotiate VIRTIO_BLK_F_BLK_SIZE if the feature is offered by the +device. When negotiated, drivers SHOULD interpret the \field{blk_size} as the +logical block size. + +If the VIRTIO_BLK_F_BLK_SIZE feature is not offered by the device, then drivers +MAY assume that the logical block size is 512 bytes. + Drivers SHOULD NOT negotiate VIRTIO_BLK_F_FLUSH if they are incapable of sending VIRTIO_BLK_T_FLUSH commands. @@ -319,6 +330,10 @@ \subsection{Device Initialization}\label{sec:Device Types / Block Device / Devic \devicenormative{\subsubsection}{Device Initialization}{Device Types / Block Device / Device Initialization} +Devices SHOULD offer VIRTIO_BLK_F_BLK_SIZE. When this feature is offered, +devices MUST initialize \field{blk_size} to a power of two greater than or +equal to 512. + Devices SHOULD always offer VIRTIO_BLK_F_FLUSH, and MUST offer it if they offer VIRTIO_BLK_F_CONFIG_WCE. @@ -879,6 +894,14 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope The length of \field{data} MUST be a multiple of 512 bytes for VIRTIO_BLK_T_IN and VIRTIO_BLK_T_OUT requests. +When the VIRTIO_BLK_F_BLK_SIZE feature is offered by the device, the length of +\field{data} SHOULD be a multiple of \field{blk_size} for VIRTIO_BLK_T_IN and +VIRTIO_BLK_T_OUT requests. + +When the VIRTIO_BLK_F_BLK_SIZE feature is offered by the device, the value of +\field{sector} (multiplied by 512) SHOULD be a multiple of \field{blk_size} for +VIRTIO_BLK_T_IN and VIRTIO_BLK_T_OUT requests. + The length of \field{data} MUST be a multiple of the size of struct virtio_blk_discard_write_zeroes for VIRTIO_BLK_T_DISCARD, VIRTIO_BLK_T_SECURE_ERASE and VIRTIO_BLK_T_WRITE_ZEROES requests. @@ -966,6 +989,16 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope for a write request if the VIRTIO_BLK_F_RO feature if offered, and MUST NOT write any data. +When the VIRTIO_BLK_F_BLK_SIZE feature is offered by the device, and the +requested \field{sector} (multiplied by 512) is not an integer multiple of the +device's \field{blk_size}, the device MAY set the \field{status} to +VIRTIO_BLK_S_IOERR for both VIRTIO_BLK_T_IN and VIRTIO_BLK_T_OUT requests. + +When the VIRTIO_BLK_F_BLK_SIZE feature is offered by the device, and the +length of the requested \field{data} is not an integer multiple of the device's +\field{blk_size}, the device MAY set the \field{status} to VIRTIO_BLK_S_IOERR +for both VIRTIO_BLK_T_IN and VIRTIO_BLK_T_OUT requests. + The device MUST set the \field{status} byte to VIRTIO_BLK_S_UNSUPP for discard, secure erase and write zeroes commands if any unknown flag is set. Furthermore, the device MUST set the \field{status} byte to -- 2.18.1
