NAME

xbdback — Xen backend paravirtualized block device interface

SYNOPSIS

pseudo-device xbdback

DESCRIPTION

The xbdback interface forms the backend part of the paravirtualized drivers used by Xen domains to offer a block device interface, similar to a hard disk. xbdback interfaces are backed either by a physical device directly, or an image file mounted through vnd(4).

All xbdback interfaces follow the “xbdbackXiY” naming convention, where ‘X’ represents the guest domain identifier, and ‘Y’ an arbitrary identifier. This identifier is usually associated to the device node as seen by the guest using major(3) and minor(3) numbers. For example, identifier “769” (0x301) means major 3 and minor 1, identified as “hda1” under Linux convention. For NetBSD, the guest device name specified in the guest configuration file does not matter, and can be chosen arbitrarily.

A xbdback interface will appear as a xbd(4) block device inside a NetBSD guest domain. In the XenStore, xbd and xbdback are identified by “vbd” (virtual block device) entries.

DIAGNOSTICS

xbd backend: attach device %s (size %d) for domain %d

Gives the device used as xbdback interface for the given guest domain, and its size, in bytes.

xbd backend 0x%x for domain %d using event channel %d, protocol %s

Gives the backend identifier, guest domain ID, event channel ID, and protocol used for block level communication.

xbdback %s: can't VOP_OPEN device 0x%x: %d

When this message appears in the system message buffer with error 16 (EBUSY), the device is likely to be already mounted. It must be unmounted first, as the system will refuse to open it a second time.

SEE ALSO

vnd(4), xbd(4), xenbus(4)

HISTORY

The xbdback driver first appeared in NetBSD 4.0.

AUTHORS

The xbdback driver was written by Manuel Bouyer <bouyer@NetBSD.org>.