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A recent proposed feature addition to the virtio block driver revealed some flaws in the API: in particular, we assume that feature negotiation is complete once a driver's probe function returns. There is nothing in the API to require this, however, and even I didn't notice when it was violated. So instead, we require the driver to specify what features it supports in a table, we can then move the feature negotiation into the virtio core. The intersection of device and driver features are presented in a new 'features' bitmap in the struct virtio_device. Note that this highlights the difference between Linux unsigned-long bitmaps where each unsigned long is in native endian, and a straight-forward little-endian array of bytes. Drivers can still remove feature bits in their probe routine if they really have to. API changes: - dev->config->feature() no longer gets and acks a feature. - drivers should advertise their features in the 'feature_table' field - use virtio_has_feature() for extra sanity when checking feature bits Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> |
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| .. | ||
| x86 | ||
| core.c | ||
| hypercalls.c | ||
| interrupts_and_traps.c | ||
| Kconfig | ||
| lg.h | ||
| lguest_device.c | ||
| lguest_user.c | ||
| Makefile | ||
| page_tables.c | ||
| README | ||
| segments.c | ||
Welcome, friend reader, to lguest. Lguest is an adventure, with you, the reader, as Hero. I can't think of many 5000-line projects which offer both such capability and glimpses of future potential; it is an exciting time to be delving into the source! But be warned; this is an arduous journey of several hours or more! And as we know, all true Heroes are driven by a Noble Goal. Thus I offer a Beer (or equivalent) to anyone I meet who has completed this documentation. So get comfortable and keep your wits about you (both quick and humorous). Along your way to the Noble Goal, you will also gain masterly insight into lguest, and hypervisors and x86 virtualization in general. Our Quest is in seven parts: (best read with C highlighting turned on) I) Preparation - In which our potential hero is flown quickly over the landscape for a taste of its scope. Suitable for the armchair coders and other such persons of faint constitution. II) Guest - Where we encounter the first tantalising wisps of code, and come to understand the details of the life of a Guest kernel. III) Drivers - Whereby the Guest finds its voice and become useful, and our understanding of the Guest is completed. IV) Launcher - Where we trace back to the creation of the Guest, and thus begin our understanding of the Host. V) Host - Where we master the Host code, through a long and tortuous journey. Indeed, it is here that our hero is tested in the Bit of Despair. VI) Switcher - Where our understanding of the intertwined nature of Guests and Hosts is completed. VII) Mastery - Where our fully fledged hero grapples with the Great Question: "What next?" make Preparation! Rusty Russell.