Kernel Log: Coming in 3.4 (Part 2) - Filesystems, storage and drivers
by Thorsten Leemhuis
Btrfs will work faster and handle errors better, Linux 3.4 already supports chipsets that Intel won't release until next year, and Greg Kroah-Hartman is putting pressure on Zcache developers to finally improve their staging code.
A Red Hat developer has made changes to code related to handling metadata in Btrfs that can improve performance in certain situations, as Oracle developer Chris Mason explains in his main git pull request for the filesystem, which is still considered to be experimental. These changes also lay some foundations to support RAID 5 and 6, Mason writes, indicating with a winking emoticon these might be for the Linux 3.5 merge window. The way Btrfs handles errors was also improved by significant contributions from a SUSE developer who worked on the changes for SUSE Linux Enterprise (SLE) 11's second service pack; the filesystem has been officially supported in this SLE version and in Oracle's Unbreakable Enterprise Kernel 2 for a few weeks now.
The Ext4 developers have removed the journal=update and resize mount options; the noacl and noxattr_user options for deactivating ACL support will be removed in Linux 3.5, as long as no one vetoes the plan.
Changes to NFSD should improve server-side support for NFS 4.1 and fix some problems related to restarting and interaction with Ext filesystems. Meanwhile, changes to the NFS client code will provide NFS support for containers and improve the ID mapper's scalability. For the first time, kernel 3.4 supports reading the qnx6fs filesystem, which uses the QNX 6 (also known as QNX RTP) real-time operating system.
Current state of development
With the release of the fifth pre-release version of Linux 3.4 late Sunday night, Linus Torvalds says that development hasn't calmed down. In fact, there were 50 per cent more commits in rc5 than in rc4.
The next pre-release version is expected to arrive early next week. With it, the development of Linux 3.4 is slowly approaching the finish line, although it is likely that there will be another RC before the final version arrives.
The dm-thin device mapper target 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. One new feature is the dm-verity device mapper target, which checks the integrity of a read-only disk while it is being read; an LWN.net article on dm-verity explains that Google is using the approach to secure the Chrome OS and Chromium OS operating systems.
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. A driver for flash host controllers that implement the Universal Flash Storage (UFS) specification has been added to the SCSI subsystem. Libfc, which takes care of various Fibre Channel hardware tasks, now supports the Fabric Device Management Interface (FDMI) as defined in the FC-GS-4 specification.
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. Extensions have been added to the Netfilter infrastructure so that administrators can define individual timeout policies for each dataflow ("connection tracking timeout infrastructure"; 1, 2 and others).