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Virtualisation

In 3.4, PCI 2.3 devices that share an interrupt line with other PCI devices on the host can be passed to KVM guests. Changes to the Xen code (1, 2 and others) enable recent versions of the Xen Hypervisor to adjust the processor speed or send the CPU into a short-term sleep state when using Linux 3.4 on the Dom0.

The SCSI subsystem now includes the virtio-scsi driver which, together with the identically named support in Qemu, is suitable for providing a device emulation that controls the data traffic between host and guest without much overhead. According to its developer, the driver is more flexible, offers better scalability and is easier to use than virtio-blk – a driver which, according to the developer, offers a similar functionality but lacks features for certain use cases.

Storage

Changes to code related to handling metadata in Btrfs can improve the performance in certain situations. The way that the still-experimental filesystem handles errors has also been improved significantly.

The MD software RAID code can now resize RAID 10 arrays in such a way that, for example, extra space in component devices can be used after the underlying disks have been exchanged for larger ones. The dm-thin device mapper target used for thin provisioning can now handle discard. It can also export a write-protected image multiple times and store the data written there in another location – this "read-only external snapshot origin" is useful for virtualisation, allowing an image of an operating system installation to be used as a common basis for multiple guest systems.

Drivers

As usual, there are a number of improvements to the drivers and infrastructure for DVB hardware, including support for the KWorld PC150-U ATSC hybrid tuner card, as well as for the AzureWave 6007 and related USB 2.0 DVB-T/C hardware. A new Realtek RTL2831U driver for DVB-T hardware has also been added.

The Brcmfmac Broadcom WLAN driver now works with the Bcm43235/6/8 USB chips, while the rt2x00 Ralink driver, starting with 3.4, supports the RT5372 WLAN chipset. The rtl8187 driver, responsible for the Realtek chip with the same name, now provides ad hoc support. A driver has been added to the Linux 3.4 kernel for Synaptics touchpads connected via USB. Samsung notebooks saw several big changes in their drivers, including one that allows them to turn on keyboard backlighting for some devices.

The Hyper-V Storage driver has moved from the staging tree to the SCSI subsystem; it was the last driver for Microsoft's virtualisation interface to leave the area designated for drivers that don't meet the kernel developers' demands for quality, which means that the Microsoft drivers may soon also start showing up in distributions that have few or no staging drivers. Microsoft presented these drivers, developed in-house, in July 2009 but didn't pay much attention to improving the code at first.

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