The last-minute merge wishlist
Linus is spending the week cruising through the Caribbean; when he returns,
just a few days will remain before the Halloween feature freeze date.
There has been a lively discussion of the patches which will be waiting for
him when he gets back. Rob Landley has compiled a list of 2.5 merge candidates
based on those
discussions. The list is a good summary of what's still waiting in the
wings, but it assumes the reader understands what the various
patches are. So here's an annotated version:
- The new kernel configuration system. The new configuration
code has been generally well received; even the Qt-based graphical
configuration tool hasn't drawn a lot of complaints. Merging seems
likely, perhaps without the graphical tools, which, Linus thinks,
might be better off outside the kernel. (Covered here October 10).
- Extended attributes and ACLs for ext2 and ext3. Ted Ts'o has
taken on the work of fixing up and submitting this patch set. There
has been some concern, based on Red Hat's having evidently pulled the
ACL patches from their 8.0 kernel during the beta stage. But it would
be surprising if this patch did not get in in some form; access
control lists are a fairly basic requirement for a lot of users. Some
Linux filesystems (JFS, XFS) already support ACLs.
- Linux Trace Toolkit. LTT is a general tool for the tracing of
events in a Linux system, in both user and kernel space. It's not
clear whether this one will get in; not everybody is convinced that
this patch needs to be in the mainline kernel. (Covered briefly on April 18).
- LVM2 and/or EVMS. The 2.5 kernel currently lacks a working
logical volume manager, but there is little consensus on which of
these two developments should fill that gap. It is possible (though
unlikely) that the next stable kernel could ship without any volume
manager at all. (Covered here last
- Shared page tables. This patch, originally by Daniel Phillips,
has since been picked up by Dave McCracken and fixed up for
inclusion. Shared page tables have a couple of benefits: they reduce
the time taken by the fork() system call (since page tables
and rmap structures need not be copied), and they reduce page table
overhead for systems (i.e. databases) using very large shared
segments. The patch has been slow to stabilize, and may appear too
risky for inclusion at this late date, but one never knows. (Covered
back in January).
- Large page support is another way of reducing overhead for
very large shared segments. A large page patch went into the kernel a
little while back (covered August 10), but it is difficult for
applications to use and does not work with shared segments, which is
where people really want this capability. A number of patches
currently exist in Andrew Morton's "-mm" tree which address these
- Dynamic probes/KProbes. This patch allows the placement of
debugger-style breakpoints at arbitrary locations within the kernel.
There is some pressure to get this one merged, but Linus has not taken
it so far.
- High-resolution timers. This longstanding patch by George
Anzinger implements the POSIX
timers specification. There are some concerns about how this
patch is implemented, and recently an
alternative version of the patch has surfaced. There is demand
for this capability; with luck some version of the patch will get in.
- Linux Kernel Crash Dumps. This is another patch which has been
around for a long time; it allows the creation of a full dump of the
kernel's state when it crashes. The purpose, of course, is to enable
vendors to debug crashes remotely. (First LWN mention: November 18, 1999).
- Console layer rewrite. This is mostly a massive cleanup
project which is getting a lot of the ancient cruft out of the console
layer while adding some new features. Parts of this work have just been finished recently.
- kexec. This relatively new patch adds a kexec()
system call that allows booting another kernel directly from Linux.
With this patch, one can reboot (possibly into another operating
system) without having to go through the whole BIOS startup routine
again. This patch is quite new and has some open issues; it may be a
better candidate for the next development series.
- USAGI IPv6. The USAGI project has been working in improved
IPv6 support for some time, and has released a comprehensive set of
patches. The word from David Miller,
however, is that the networking developers want to take a different
direction for IPv6 support (and CryptoAPI and IPSec as well).
"We will be incorporating lots of ideas and small code pieces
from USAGI's work, but most of the core engine will be a new
implementation." They intend to have this work complete and
ready for merging by Linus's return. That will be a big pile of new
code, however, that few people have seen.
- uClinux. This is the classic patch for running Linux on
systems with no memory management unit. It has recently been ported
forward to 2.5 and proposed for submission; Alan Cox has merged it
into his tree. New architectures are usually not that hard to get in,
and there has not been much opposition to this one.
- sys_epoll. This is the new incarnation of the
/dev/epoll patch, which seeks to make a faster, more scalable
poll() interface. The patch has been reworked into system
call form now, and might just get past Linus this time.
- New CD burning patch. This brand-new patch from Jens Axboe
(finally) allows the use of DMA operations when burning CDs. It also
turns burning into a zero-copy operation. The result should be
faster, more reliable CD writing. (Patch posted on October 23).
- In-kernel module loader. Rusty Russell's in-kernel module
loader patch is advertised as being safer and more capable than the
old, user-space implementation while simultaneously requiring less
kernel code. (Covered here September 26).
- Boot/module parameter rework. This patch made Rob's list,
but there has been little work in this area recently. Many of the
ideas from this work have been folded into the device model code.
(Covered here in June as part of the
Kernel Summit writeup).
- Hotplug CPU. This is another Rusty Russell patch which has
been around for a while. It seems to work, but has few users - most
of us don't pull processors out of running systems. Its application,
of course, is for high-availability systems and such.
- The unlimited groups patch. This is a recent patch which would
allow the kernel to support very large numbers of groups - the
developers have tested it with 10,000 at a time.
- Initramfs. This patch allows a disk image to be appended
directly to the kernel executable; it would then contain much of the
bootstrap code that is now found in the kernel itself. This patch
reduces the size of the kernel itself while making it far easier for
users to customize the early bootstrap process; it could be especially
useful for embedded systems. Much of this code has been ready for
some time; it has mostly been a matter of getting the user-space side
of things into shape. (Covered here August, 2001 and January, 2002).
- ReiserFS 4. This is a completely new version of the Reiser
filesystem; almost nobody has seen it, but it is supposed to show up
shortly in condition for merging.
- A larger dev_t. Supporting larger numbers of devices was high
on the list of things to do before the 2.5 series even started, but
the enlargement of the dev_t type still has not happened.
This one is on Alexander Viro's plate; he has been pushing through
other changes (in the block layer, mostly) that are prerequisites to
the dev_t change. (Covered here December, 2001).
That, of course, is a rather lengthy list. Much of this stuff is clearly
not going to get in to the 2.5 kernel - at least, not if the feature freeze
holds as intended. At this point, it's mostly a matter of waiting until
Linus returns and seeing what he decides to do.
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