85 lines
3.9 KiB
Markdown
85 lines
3.9 KiB
Markdown
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# SPDK virtio bdev module
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This directory contains an experimental SPDK virtio bdev module.
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It currently supports very basic enumeration capabilities for
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virtio-scsi devices as well as read/write operations to any
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SCSI LUNs discovered during enumeration.
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It supports two different usage models:
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* PCI - This is the standard mode of operation when used in a guest virtual
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machine, where QEMU has presented the virtio-scsi controller as a virtual
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PCI device. The virtio-scsi controller might be implemented in the host OS
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by SPDK vhost-scsi, kernel vhost-scsi, or a QEMU virtio-scsi backend.
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* User vhost - Can be used to connect to an SPDK vhost-scsi target running on
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the same host.
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Note that 1GB hugepages is pretty much required to use this driver in
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user-vhost mode. vhost protocol requires passing a file descriptor for
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each region of memory being shared with the vhost target. Since DPDK opens
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every huge page explicitly, it is fairly limited on how many file descriptors
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it can pass due to the VHOST_MEMORY_MAX_NREGIONS limit of 8.
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Use the following configuration file snippet to enumerate a virtio-scsi PCI
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device and present its LUNs as bdevs. Currently it will only work with
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a single PCI device.
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~~~{.sh}
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[Virtio]
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Dev Pci
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~~~
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Use the following configuration file snippet to enumerate an SPDK vhost-scsi
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controller and present its LUNs as bdevs. In this case, the SPDK vhost-scsi
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target has created an SPDK vhost-scsi controller which is accessible through
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the /tmp/vhost.0 domain socket.
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~~~{.sh}
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[Virtio]
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Dev User /tmp/vhost.0
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~~~
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Todo:
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* Support multiple PCI devices, including specifying the PCI device by PCI
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bus/domain/function.
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* Define SPDK virtio bdev request structure and report it as the context
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size during module initialization. This will allow the module to build
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its request and response in per-bdev_io memory.
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* Asynchronous I/O - currently the driver polls inline for all completions.
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Asynchronous I/O should be used for both enumeration (INQUIRY, READ CAPACITY,
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etc.) as well as read/write I/O.
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* Add unmap support.
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* Add I/O channel support. Includes requesting correct number of queues
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(based on core count). Fail device initialization if not enough queues
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can be allocated.
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* Add RPCs.
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* Break out the "rte_virtio" code into a separate library that is not
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linked directly to the bdev module. This would allow that part of the
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code to potentially get used and tested outside of the SPDK bdev framework.
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* Check for allocation failures in bdev_virtio.c code.
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* Change printfs to SPDK_TRACELOGs (or just remove altogether).
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* Add virtio-blk support. This will require some rework in the core
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virtio code (in the rte_virtio subdirectory) to allow for multiple
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device types.
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* Bottom out on whether we should have one virtio driver to cover both
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scsi and blk. If these should be separate, then this driver should be
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renamed to something scsi specific.
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* Add reset support.
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* Finish cleaning up "eth" references. This includes filenames like
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virtio_ethdev.c and "eth" in various API calls.
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* Improve the virtio_xmit_pkts and virtio_recv_pkts interfaces. Should not
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reference the virtio_hw tx_queues directly. Should have a more opaque API.
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* Understand and handle queue full conditions.
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* Clear interrupt flag for completions - since we are polling, we do not
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need the virtio-scsi backend to signal completion.
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* Check interrupt flag for submission. If the backend requires an interrupt,
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we need to signal it.
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* Change read/write to use READ_16/WRITE_16 to handle LBA > 4G. We can add
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a basic check and bail during enumeration if INQUIRY indicates the LUN does
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not support >= SBC-3.
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* Automated test scripts for both PCI and vhost-user scenarios.
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* Document Virtio config file section in examples. Should wait on this until
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enough of the above items are implemented to consider this module as ready
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for more general use.
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* Specify the name of the bdev in the config file (and RPC) - currently we
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just hardcode a single bdev name "Virtio0".
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