the idea of closing the
merge window rather earlier than expected, Linus did, in the end, keep it
open until September 16. He repeated past grumbles about
maintainers who send their pull requests at the very end of the merge
window, though; increasingly, it seems that wise maintainers should behave
as if the merge window were a single week in length. Pull requests that
are sent too late run a high risk of being deferred until the next
In the end, 9,479 non-merge changesets were pulled into the mainline
repository for the 3.12 merge window; about 1,000 of those came in after
the writing of last week's summary.
Few of the changes merged in the final days of the merge window were hugely
exciting, but there have been a number of new features and improvements.
Some of the more significant, user-visible changes include:
- Unlike its predecessor, the 3.12 kernel will not be known as "Linux
for Workgroups." Instead, for reasons that are not entirely clear,
the new code name was "Suicidal Squirrel" for a few days; it then was
changed to "One giant leap for frogkind."
- It is now possible to provide block device partition tables on the
kernel command line; see Documentation/block/cmdline-partition.txt
- The memory management subsystem has gained the ability to migrate huge
pages between NUMA nodes.
- The Btrfs filesystem has the beginning of support for offline
deduplication of data blocks. A new ioctl() command
(BTRFS_IOC_FILE_EXTENT_SAME) can be used by a user-space
program to inform the kernel of extents in two different files that
contain the same data. The kernel will, after checking that the
data is indeed the same, cause the two files to share a single copy of
- The HFS+ filesystem now supports POSIX access control lists.
- The reliable out-of-memory killer
patches have been merged. This work should make OOM handling more
robust, but it could possibly confuse user-space applications by
returning "out of memory" errors in situations where such errors were
not seen before.
- The evdev input layer has gained a new EVIOCREVOKE
ioctl() command that revokes all access to a given file
descriptor. It can be used to ensure that no evil processes lurk on
an input device across sessions. See this
patch for an example of how this functionality can be used.
- New hardware support includes:
MOXA ART real-time clocks,
Freescale i.MX SoC temperature sensors,
Allwinner A10/A13 watchdog devices,
Freescale PAMU I/O memory management units,
TI LP8501 LED controllers,
Cavium OCTEON GPIO controllers, and
Mediatek/Ralink RT3883 PCI controllers,
Intel i40e Ethernet interfaces.
Changes visible to kernel developers include:
- The seqlock locking primitive has gained a new "locking reader" type.
Normally, seqlocks allow for data structures to be changed while being
accessed by readers; the readers are supposed to detect the change (by
checking the sequence number) and retry if need be. Some types of
readers cannot tolerate changes to the structure, though; in current
kernels, they take an expensive write lock instead. The "locking
reader" lock will block writers and other locking readers, but allow
normal readers through. Note that locking readers could share
access with each other;
the fact that this sharing does not happen now is an implementation
limitation. The functions for working with this type of
void read_seqlock_excl(seqlock_t *sl);
void read_sequnlock_excl(seqlock_t *sl);
There are also the usual variants for blocking hardware and software
interrupts; the full set can be found in
- The new shrinker API has been merged.
Most code using this API needed to be changed; the result should be
better performance and a better-defined, more robust API. The new
"LRU list" mechanism that was a part of that patch set has also been
- The per-CPU IDA ID allocator patch set
has been merged.
Now begins the stabilization phase for the 3.12 kernel. If the usual
pattern holds, the final release can be expected on or shortly after
Halloween; whether it turns out to be a "trick" or a "treat" depends on how
well the testing goes between now and then.
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