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a6bd8e1303
Took some cycles to re-read the Lguest Journey end-to-end, fix some rot and tighten some phrases. Only comments change. No new jokes, but a couple of recycled old jokes. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
63 lines
2.3 KiB
C
63 lines
2.3 KiB
C
#ifndef _LINUX_LGUEST_LAUNCHER
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#define _LINUX_LGUEST_LAUNCHER
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/* Everything the "lguest" userspace program needs to know. */
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#include <linux/types.h>
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/*D:010
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* Drivers
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*
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* The Guest needs devices to do anything useful. Since we don't let it touch
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* real devices (think of the damage it could do!) we provide virtual devices.
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* We could emulate a PCI bus with various devices on it, but that is a fairly
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* complex burden for the Host and suboptimal for the Guest, so we have our own
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* simple lguest bus and we use "virtio" drivers. These drivers need a set of
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* routines from us which will actually do the virtual I/O, but they handle all
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* the net/block/console stuff themselves. This means that if we want to add
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* a new device, we simply need to write a new virtio driver and create support
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* for it in the Launcher: this code won't need to change.
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*
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* Virtio devices are also used by kvm, so we can simply reuse their optimized
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* device drivers. And one day when everyone uses virtio, my plan will be
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* complete. Bwahahahah!
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*
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* Devices are described by a simplified ID, a status byte, and some "config"
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* bytes which describe this device's configuration. This is placed by the
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* Launcher just above the top of physical memory:
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*/
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struct lguest_device_desc {
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/* The device type: console, network, disk etc. Type 0 terminates. */
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__u8 type;
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/* The number of virtqueues (first in config array) */
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__u8 num_vq;
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/* The number of bytes of feature bits. Multiply by 2: one for host
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* features and one for Guest acknowledgements. */
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__u8 feature_len;
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/* The number of bytes of the config array after virtqueues. */
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__u8 config_len;
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/* A status byte, written by the Guest. */
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__u8 status;
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__u8 config[0];
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};
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/*D:135 This is how we expect the device configuration field for a virtqueue
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* to be laid out in config space. */
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struct lguest_vqconfig {
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/* The number of entries in the virtio_ring */
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__u16 num;
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/* The interrupt we get when something happens. */
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__u16 irq;
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/* The page number of the virtio ring for this device. */
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__u32 pfn;
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};
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/*:*/
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/* Write command first word is a request. */
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enum lguest_req
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{
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LHREQ_INITIALIZE, /* + base, pfnlimit, pgdir, start */
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LHREQ_GETDMA, /* No longer used */
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LHREQ_IRQ, /* + irq */
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LHREQ_BREAK, /* + on/off flag (on blocks until someone does off) */
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};
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#endif /* _LINUX_LGUEST_LAUNCHER */
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