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It does this by obscuring each storage >> +controller from the OS, but allowing a single driver to be loaded that would >> +control each storage controller. A Volume Management Device (VMD) provides a >> +single device for a single storage driver. The VMD resides in the IIO root >> +complex and it appears to the OS as a root bus integrated endpoint. In the IIO, >> +the VMD is in a central location to manipulate access to storage devices which >> +may be attached directly to the IIO or indirectly through the PCH. Instead of >> +allowing individual storage devices to be detected by the OS and allow it to >> +load a separate driver instance for each, the VMD provides configuration >> +settings to allow specific devices and root ports on the root bus to be >> +invisible to the OS. > > This doesn't really capture how the vmd driver works here, though. The > linux driver doesn't control or hide any devices connected to it; it > just creates a host bridge to its PCI domain, then exposes everything to > the rest of the OS for other drivers to bind to individual device > instances that the pci bus driver finds. Everything functions much the > same as if VMD was disabled. I was trying more to provide an overview of how the VMD device itself works here and not the driver. The driver is fairly simple; it's how the device works that seems to confuse people :). Do you have a suggestion on what you would like to see here? Paul