75 lines
3.4 KiB
Plaintext
75 lines
3.4 KiB
Plaintext
This directory contains an USB Mass Storage Bulk-Only driver. It uses
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the Usb session interface to access the USB device and provides Genode's
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Block service to its client.
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Behavior
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--------
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This driver only supports USB Mass Storage Bulk-Only devices that use the
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SCSI Block Commands set (direct-access). Devices using different command
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sets, e.g, SD/HC devices or some external disc drives will not work properly
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if at all. The following configuration snippets demonstrates how to use the
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driver:
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!<start name="usb_block_drv">
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! <resource name="RAM" quantum="4M"/>
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! <provides> <service name="Block"/> </provides>
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! <config label="usb_stick" report="yes" writeable="yes" interface="0" lun="0" reset_device="no" verbose_scsi="no"/>
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! <route>
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! <service name="Usb"> <child name="usb_drv"/> </service>
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! <any-service> <parent/> <any-child/> </any-service>
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! </route>
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!</start>
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The drivers 'config' node features a few attributes. First, there is the 'label'
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attribute. This attribute specifies the label used when opening the Usb session
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connection. A matching policy has to be configured at the USB host controller
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driver:
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!<start name="usb_drv">
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! <resource name="RAM" quantum="12M"/>
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! <provides><service name="Usb"/></provides>
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! <config uhci="yes" ehci="yes" xhci="yes">
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! <raw>
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! <policy label="usb_block_drv -> usb_stick" vendor_id="0x13fe" product_id="0x5200"/>
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! </raw>
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! </config>
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!</start>
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For static configurations the 'label' value may be chosen freely or may even
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be ommitted entirely. On the other hand it is best for dynamic configurations
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to choose a unique label, e.g. 'usb-<bus>-<dev>', at run-time (this most likely
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involves other components that generate configurations for the 'usb_block_drv'
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as well as the 'usb_drv').
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The second attribute is 'report'. If its value is 'yes' the driver
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will generate a 'devices' report that contains meta information about the
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USB device it is accessing and hence the Block session it is provding, e.g.:
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!<devices>
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! <device vendor="QEMU" product="QEMU USB HARDDRIVE" block_size="512" block_count="8192" writeable="no"/>
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!</devices>
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The report contains a 'device' node that includes the device's vendor name and
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the product description as well as its block size and the number of blocks.
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Although the parent node is called 'devices' the driver is only able to access
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one and the same device and the report will therefore always contain one device
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only.
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In addition to other attributes that can be used to configure sepecific aspects
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of the driver. The 'writeable' attribute denotes the permission of the Block
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session client to write to the USB device. Independent thereof the driver will
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query the device and will set the Block session operations accordingly. The
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'interface' specifies the USB interface the driver should use. If the device
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provides multiple SCSI devices the 'lun' attribute is used to select the right
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one. When 'reset_device' is enabled, a 'bulk-only mass storage reset' command
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is sent to the device at the beginning of the initialization step. This command
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caused problems on at least one device, so it is omitted by default. The
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'verbose_scsi' attribute can be useful for debugging.
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The configuration of the USB block driver cannot be changed at run-time. The
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driver is either used in a static system configuration where it is configured
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once or in case of a dynamic system configuration a new driver instance with
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a proper configuration is created on demand.
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