Significant improvements coming in Linux 3.5
Linus Torvalds published the first Linux 3.5 release candidate on Saturday night, although the official release email wasn't sent until Sunday afternoon. As usual, the first RC of the new kernel version signals the end of the merge window phase at the beginning of the development cycle, during which nearly all of the major changes are made. Aside from a few stragglers, the function set Linux 3.5-rc1 offers should be almost identical to the one in the 3.5 kernel, which is expected to be released in late July or early August.
In the approximately two weeks since Linux 3.4 was released, the kernel developers have integrated features such as uprobes (userspace probes). These can be used by Systemtap and the kernel's own perf tracing tool to analyse the runtime behaviour of userspace programs. Other important additions to Linux 3.5 include some patches to internal logging functions, championed by Udev maintainer Kay Sievers, which should improve the structured analysis of event logs.
Simple Kernel-based Mode Setting (KMS) drivers for the graphics chips from the ASpeed Technologies 2000 series and the Matrox G200 series were added to the Direct Rendering Manager (DRM); a KMS driver for the Cirrus chip that is emulated by Qemu was also merged. The drivers allow screen resolution to be configured but do not use any of the graphics chips' acceleration functions.This, however, is not a big loss where the first two chips are concerned, as they mostly tend to be used in servers. The Radeon DRM driver should provide modern graphics chips with better HDMI audio support and tease a little more performance out of the Evergreen GPUs that are mainly used for graphics hardware in the Radeon HD 5000 series. Further foundations were also laid to better support hybrid graphics setups, where a more powerful graphics chip is only turned on when it is needed.
Kernel 3.5 can now also use FireWire or the USB Attached SCSI Protocol (UASP) to serve as a SCSI target that can be accessed by other systems ("SCSI host" in the SCSI nomenclature); many systems produced by Apple have had this kind of "FireWire target disk mode" for a while now. Linux 3.5 will also be able to function as a SCSI target using QLogic fibre channel HBAs from the 2400, 2500 and 2600 series.
Writeback handling was optimised in the Btrfs filesystem, although support for RAID 5 and 6 was not added to the filesystem due to known corruption problems in the current code. The Ext4 filesystem can now add checksums to its metadata to help recognise data tampering. The network subsystem now includes the CODEL active queue management packet scheduler which is designed to help work against the "bufferbloat" problem. The new TCP connection repair feature should prevent problems with network data traffic after containers have been moved to another host. Meanwhile, the kernel now uses the seccomp filters mechanism, which filters function commands, and user namespace enhancements to secure containers better. Over the coming weeks, the Kernel Log series at The H Open will discuss these additions and various other new features in Linux 3.5 in more detail.