"I do think 'next' as it is has a few issues that either need to be fixed (unlikely - it's not the point of next) or just need to be aired as issues and understood," noted Linus Torvalds about the linux-next development tree, originally designed as a way to get subsystem maintainers more involved in managing merge conflicts. Linus continued, "I don't think anybody wants it to go away. The question in my mind is more along the way of how/whether it should be changed. There was some bickering about patches that weren't there, and some about how _partial_ series were there but then the finishing touches broke things."
He listed his two primary concerns as, "I don't think it does 'quality control', and I think that's pretty fundamental," and, "I don't think the 'next' thing works as well for the occasional developer that just has a few patches pending as it works for subsystem maintainers that are used to it." Linus continued, "I don't think either of the above issues is a 'problem' - I just think they should be acknowledged. I think 'next' is a good way for the big subsystem developers to be able to see problems early, but I really hope that nobody will _ever_ see next as a 'that's the way into Linus' tree', because for the above two reasons I do not think it can really work that way." Andrew Morton noted, "a lot of the bugs which hit your tree would have been quickly found in linux-next too," then added, "but it's all shuffling deckchairs, really. Are we actually merging better code as a reasult of all of this? Are we being more careful and reviewing better and testing better? Don't think so."
"It's two weeks (and one day), and the merge window is over," began Linus Torvalds, announcing the 2.6.27-rc1 kernel. He continued, "finally. I don't know why, but this one really did feel pretty dang busy. And the size of the -rc1 patch bears that out - at 12MB, it's about 50% bigger than 26-rc1 (but not that much bigger than 24/25-rc1, so it's not like it's anything unheard of)." He reflected, "the pure size of the -rc's _is_ making me a bit nervous, though. Sure, it means that we are good at merging it all, but I have to say that I sometimes wonder if we don't merge too much in one go, and even our current (fairly short) release cycle is actually too big." As for the actual changes, Linus explained:
"Much of -rc1 was in linux-next, but certainly not everything. We'll see how that whole thing ends up evolving - it certainly didn't solve all problems, and there was some bickering about things that weren't there (and some things that mostly were ;), but maybe it helped. There's a ton of new stuff in there, but at least personally the interesting things are the BKL pushdown and perhaps the introduction of the lockless get_user_pages_fast(). The build system also got updated to allow moving the architecture include files ('include/asm-xyz') into the architecture subdirectories ('arch/xyz/include/asm'), and sparc seems to have taken advantage of that already."
Other changes Linus highlighted included merging the UBI filesystem, as well as, "tracing, firmware loading, continued x86 arch merging, and moving more code to generic support (unified generic IPI handling, coherent dma memory allocation, show_mem etc). Bootmem rewrites. [And] some support for further scalability (ie 4k cpu cores)."
"Oh great, not yet-another-kernel-tree, just what the world needs..." began Greg KH, continuing, "yes, this is an announcement of a new kernel tree, linux-staging." He explained:
"In a long and meandering thread with some of the other kernel developers a week or so ago, it came up that there is no single place for companies and developers to put their code for testing while it gets cleaned up for submission into the kernel tree. All of the different subsystems have trees, but they generally only want code that is about to go into this release, or the next one. For stuff that is farther off, there is no place to go. So, here's the tree for it."
In a readme created for the new tree, Greg adds, "the linux-staging tree was created to hold drivers and filesystems and other semi-major additions to the Linux kernel that are not ready to be merged at this point in time." He also requested that the new tree be included in Linux -next, leading Theodore Ts'o to ask, "does this mean that the nature of linux-next is changing? I thought the whole point of linux-next was only to have what would be pushed to Linus in the near future, so we could check for patch compatibility issues." Greg explained that he was hoping for an exception for his new -staging tree as it only includes whole new drivers and filesystems, not changes to existng features, "there is stuff that users can use to get hardware to work that currently is not supported on kernel.org kernels at all." As an example he noted, "there are 2 big network drivers in there that support a wide range of devices that some people would like to see working :)"
Discussing the latest breakage of the linux-next tree, Stephen Rothwell noted that the problem went unnoticed due to the arm tree not currently being included, "this is why I would have liked you to participate in the linux-next tree ...". Arm maintainer Russell King questioned the usefulness, saying, "linux-next will not give me anything which -mm isn't giving me. As I said in the discussion, linux-next value is _very_ small for me. Sorry but true." Several stepped in to offer some reasons that the linux-next tree is useful.
Andrew Morton noted, "putting arm into linux-next means that Stephen (and git) handle the merges rather than having me (and not-git) do it. Which helps me. I expect that linux-next will get a lot more cross-compilation testing than -mm. Which helps you." Greg KH added, "getting your stuff into linux-next would provide a public place for others to base off of, making it easier for them to send patches to you ensuring that they apply properly. Which in the end, will help others be able to contribute easier, and help you by getting patches you do not need to rebase yourself." Stephen Rothwell summarized the advantages for a maintainer:
"5 times a week your tree gets merged with lots of other code destined for Linus' next release. From this you get to find out about things in other trees that clash with yours. This tree gets built on several architectures for several configs (including arm). So you find out if other trees will break yours. I am happy to build more (basically all) the arm configs as I have offered before."
"Now that we are (presumably) approaching the next merge window, can I ask what use (if any) will you be making of the linux-next tree? Alternatively, is there any information you want from it?" Stephen Rothwell asked regarding the tree he started maintaining last month for tracking upcoming stable merges.
Andrew Morton replied, "afacit it's already working. The level of merge and build errors in the subsystem trees this time around is a tiny fraction of what it was at the same stage in 2.6.24-rcX." He went on to note, "there are 60 or 80 "susbsytem" trees hosted in -mm at present," adding:
"I need to find a way to a) get matureish parts of those trees into linux-next and to b) base the rest of -mm off linux-next. I haven't started thinking about that yet. There seem to be some trees which aren't yet in linux-next, some of them significant."
"Andrew [Morton] was looking for someone to run a linux-next tree that just contained the subsystem git and quilt trees for 2.6.x+1 and I (in a moment of madness) volunteered. So, this is to announce the creating of such a tree," began Stephen Rothwell, resulting in a lengthy thread discussing the current Linux kernel development process. In a follow up email announcing the first linux-next release, Stephen went on to explain, "it has two branches - master and stable. Stable is currently just Linus' tree and will never rebase. Master will rebase on an almost daily basis (maybe slower at the start)." He then detailed the master branch:
"The tree consists of subsystem git and quilt trees. Currently, the quilt trees are integrated by importing them into appropriately based git branches and then merging those branches. This has the advantage that any conflict resolution will onlt have to happen once at the merge point rather than, possibly, several times during the series. However, I am considering just applying the quilt trees on top of the current tree to get a result more like Linus' tree - we will see. The git trees are obviously just merged."
One of the goals of the new tree is to get subsystem maintainers more involved in managing merge conflicts by quickly notifying all involved when things break, and automatically dropping the offenders until build problems are fixed. Andrew plans to base his -mm kernel on the new linux-next tree, providing a stabler test branch for code before it's merged into Linus' mainline kernel tree.