2.6.38 merge window part 2

As of the 2.6.38-rc1 release, some 7616 non-merge changesets had been pulled into the mainline kernel. A number of significant changes have been merged since last week's summary; the most interesting changes visible to users are:

• The transparent huge pages feature has been merged. THP attempts to maximize the use of huge pages in the system (boosting performance) without requiring application changes or administrator overhead.

• A new tool called turbostat has been added; it can be used to obtain various types of performance statistics from Intel processors. Also added is x86_energy_perf_policy, which can be used to tweak the performance/power usage tradeoff on Intel CPUs.

• The taskstats API has been changed to use different alignments for returned values; this may break applications which were dependent on the old arrangement.

• The kernel can now synchronize its internal time to an external pulse-per-second (PPS) signal with a high degree of accuracy. The kernel has also gained the ability to generate (and accept) PPS signals on a parallel port, assuming one can still find a computer with such a port.

• The x86 architecture can now boot XZ-compressed kernels.

• Basic support for multitouch panels has been added to the human input devices (HID) layer.

• The kernel now has support for the RFC4106 AES-GCM cryptographic algorithm.

• The fallocate() system call can now be used to punch holes in the middle of files. Currently this feature is supported by XFS and OCFS2.

• The XFS filesystem supports the FITRIM ioctl(), allowing discard operations to be initiated from user space. "This is not intended to be run during normal workloads, as the freepsace btree walks can cause large performance degradation."

• The LIO SCSI target core has been merged.

• The block I/O bandwidth controller can now be used with hierarchical control groups.

• The block layer has a new "events handling" mechanism. What that means is that detection of device events (the insertion of an optical disc, for example) can be done in the drivers, eliminating the need to poll devices from user space.

• The device mapper dm-crypt target has a new "multikey" mode whereby different blocks can be encrypted with different keys. The crypt target is also now able to access encrypted partitions created with the out-of-tree loop-AES package.

• The device mapper has gained the ability to manage RAID 4/5/6 volumes using the MD RAID drivers.

• The clone() system call no longer honors the long-deprecated CLONE_STOPPED flag.

• The btrfs filesystem has gained support for read-only snapshots and LZO compression.

• New drivers:
  • Systems and processors: ALPHAPROJECT AP-SH4A-3A and AP-SH4AD-0A reference boards, Acme Systems srl FOX G20 boards, GeoSIG GS_IA18_S boards, and Atheros AR71XX/AR724X/AR931X SoCs.

  • Audio: HP t5325 audio devices, Realtek alc562x codecs, Wolfson Micro WM8770 and WM8995 codecs, Wolfson Micro WM8958 multi-band compressors, and Wolfson Micro WM8737 analog-to-digital converters.

  • Input: Austria Microsystem AS5011 joysticks.

  • Miscellaneous: NXP Semiconductors PN544 near-field communication chips, Oki Semiconductor ML7213 IOH GPIO controllers, Freescale MC13892 PMIC regulators, Freescale MCF548x watchdog timers, TI TPS6524X Power regulators, AMD/ATI SP5100 TCO timer/watchdog chipsets, Atheros AR71XX/AR724X/AR913X hardware watchdogs, nVidia TCO timer/watchdog devices, Intel EG20T platform controller hubs, and Maxim MAX17042/8997/8966 fuel gauges.

Changes visible to kernel developers include:

• ktest.pl, a script which can automate the process of building, testing, and bisecting kernels, has been added to the tools directory.

• The "%pK" format specifier can be used to print the value of potentially sensitive kernel pointers, especially in places like /proc files. The behavior of this specifier depends on the value of /proc/sys/kernel/kptr_restrict; a value of zero means that kernel pointers will be printed as usual, one causes pointers to be printed as zero for users without CAP_SYSLOG, and two hides the pointers for all users.

• cdev_index() has been removed; since there are no in-kernel users, nobody is likely to notice.

• The new function kref_test_and_get() will take a reference only if the current reference count is not zero.

• Some new dentry operations have been added to support automounters within the VFS.

• The fallocate() filesystem callback has been moved from struct inode_operations to struct file_operations.

With the 2.6.38 feature set complete, the process of stabilizing all of this new code can continue; expect a final 2.6.38 release sometime in late March.

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