diff options
| -rw-r--r-- | content.tex | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/content.tex b/content.tex index 9cc958d..b558654 100644 --- a/content.tex +++ b/content.tex @@ -3822,7 +3822,7 @@ Facilities of a Virtio Device / Virtqueues / Message Framing}. The virtio block device is a simple virtual block device (ie. disk). Read and write requests (and other exotic requests) are -placed in the queue, and serviced (probably out of order) by the +placed in one of its queues, and serviced (probably out of order) by the device except where noted. \subsection{Device ID}\label{sec:Device Types / Block Device / Device ID} @@ -3830,9 +3830,14 @@ device except where noted. \subsection{Virtqueues}\label{sec:Device Types / Block Device / Virtqueues} \begin{description} -\item[0] requestq +\item[0] requestq1 +\item[\ldots] +\item[N] requestqN \end{description} + N=1 if VIRTIO_BLK_F_MQ is not negotiated, otherwise N is set by + \field{num_queues}. + \subsection{Feature bits}\label{sec:Device Types / Block Device / Feature bits} \begin{description} @@ -3857,6 +3862,8 @@ device except where noted. \item[VIRTIO_BLK_F_CONFIG_WCE (11)] Device can toggle its cache between writeback and writethrough modes. +\item[VIRTIO_BLK_F_MQ (12)] Device supports multiqueue. + \item[VIRTIO_BLK_F_DISCARD (13)] Device can support discard command, maximum discard sectors size in \field{max_discard_sectors} and maximum discard segment number in \field{max_discard_seg}. @@ -3885,6 +3892,9 @@ The \field{capacity} of the device (expressed in 512-byte sectors) is always present. The availability of the others all depend on various feature bits as indicated above. +The field \field{num_queues} only exists if VIRTIO_BLK_F_MQ is set. This field specifies +the number of queues. + The parameters in the configuration space of the device \field{max_discard_sectors} \field{discard_sector_alignment} are expressed in 512-byte units if the VIRTIO_BLK_F_DISCARD feature bit is negotiated. The \field{max_write_zeroes_sectors} @@ -3913,7 +3923,8 @@ struct virtio_blk_config { le32 opt_io_size; } topology; u8 writeback; - u8 unused0[3]; + u8 unused0; + u16 num_queues; le32 max_discard_sectors; le32 max_discard_seg; le32 discard_sector_alignment; @@ -3973,6 +3984,10 @@ according to the native endian of the guest rather than \field{max_write_zeroes_sectors} and \field{max_write_zeroes_seg} can be read to determine the maximum write zeroes sectors and maximum number of write zeroes segments for the block driver to use. + +\item If the VIRTIO_BLK_F_MQ feature is negotiated, \field{num_queues} field + can be read to determine the number of queues. + \end{enumerate} \drivernormative{\subsubsection}{Device Initialization}{Device Types / Block Device / Device Initialization} @@ -4024,7 +4039,7 @@ legacy interface: \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Operation} -The driver queues requests to the virtqueue, and they are used by +The driver queues requests to the virtqueues, and they are used by the device (not necessarily in order). Each request is of form: \begin{lstlisting} |