2.6.34 Merge window, part 2

• Signal-handling semantics have been changed so that "synchronous" signals (SIGSEGV, for example) are delivered prior to asynchronous signals like SIGUSR1. This fixes a problem where synchronous signal handlers could be invoked with the wrong context, something that apparently came up occasionally in WINE. Users are unlikely to notice the change, but it is a slight semantics change that developers may want to be aware of.

• A new Nouveau driver with an incompatible interface has been merged; as of this writing, it will break all user-space code which worked with the older API. See this article for more information on the Nouveau changes. Nouveau also no longer needs external firmware for NV50-based cards.

• The direct rendering layer now supports "VGA switcheroo" on systems which provide more than one graphical processor. For most needs, a simple, low-power GPU can be used, but the system can switch to the more power-hungry GPU when its features are needed.

• The umount() system call supports a new UMOUNT_NOFOLLOW flag which prevents the following of symbolic links. Without this flag, local users who can perform unprivileged mounts can use a symbolic link to unmount arbitrary filesystems.

• The exofs filesystem (for object storage devices) has gained support for groups and for RAID0 striping.

• The LogFS filesystem for solid-state storage devices has been merged.

• New drivers:
  • Media: Wolfson Microelectronics WM8994 codecs, and Broadcom Crystal HD video decoders (staging).

  • Miscellaneous: Freescale MPC512x built-in DMA engines, Andigilog aSC7621 monitoring chips, Analog Devices ADT7411 monitoring chips, Maxim MAX7300 GPIO expanders, HP Processor Clocking Control interfaces, DT3155 Digitizers (staging), Intel SCH GPIO controllers, Intel Langwell APB Timers, ST-Ericsson Nomadik/Ux500 I2C controllers, Maxim Semiconductor MAX8925 power management ICs, Max63xx watchdog timers, Technologic TX-72xx watchdog timers, and Hilscher NetX based fieldbus cards.

Changes visible to kernel developers include:

• There has been a subtle change to the early boot code, wherein the kernel will open the console device prior to switching to the root filesystem. That eliminates problems where booting fails on a system with an empty /dev directory because the console device cannot be found, and eliminates the need to use devtmpfs in such situations.

• The kprobes jump optimization patch has been merged.

• The write_inode() method in struct super_operations is now passed a pointer to the relevant writeback_control structure.

• Two new helper functions - sysfs_create_files() and sysfs_remove_files() - ease the process of creating a whole array of attribute files.

• The show() and store() methods of struct class_attribute have seen a prototype change: the associated struct class_attribute pointer is now passed in. A similar change has been made to struct sysdev_class_attribute.

• The sem lock found in struct device should no longer be accessed directly; instead, use device_lock() and device_unlock().

At "only" 6000 changesets, 2.6.34 looks like a relatively calm development cycle; both 2.6.32 and 2.6.33 had over 8000 changesets by the time the -rc1 release came out. It may be that there is less work to be done, but it may also be that some trees got caught out in the cold by Linus's decision to close the merge window early. Linus suggested that he might yet consider a few pull requests, so we might still see some new features added to this kernel; stay tuned.