Merging xen/dom0/backend/blktap2 ..

Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

is an overall pita and I've had the pleasure several times now.

There's a bunch of deltas at the very bottom which look to me like
unrelated arch stuff which never made it anywhere else. Additional stuff
which was obsoleted/deprecated (e.g. the pte zapping changes) but
apparently never reverted.  Plus some xen-related hunks nobody would
dare to admit to ever have seen before (iirc we had such a thread a
while ago).

After a lengthy checkout/--patch orgy, the compound diff looks quite
simple, in contrast.

My hope is one could either either revert a whole lot in there (does
this help reliably during merges? I guess it would). Or, maybe helpful
in order order to further reduce noise, rebase that tree on some more
solid root. Dropping quite a bit of garbage here and there. Then call
that a new branch and phase out the old one.

>From what I've tried so far, git seems to be reasonably smart about
remerging such stuff again later. Then again, just reverting might help
cleaning up elsewhere.

Preferences? Are there better ways? Or rather just keep it the way it
is?

Thanks,
Daniel

    Conflicts:
        arch/x86/include/asm/io.h
        arch/x86/include/asm/paravirt.h
        arch/x86/include/asm/xen/page.h
        arch/x86/kernel/cpu/mtrr/amd.c
        arch/x86/kernel/cpu/mtrr/centaur.c
        arch/x86/kernel/cpu/mtrr/cyrix.c
        arch/x86/kernel/cpu/mtrr/generic.c
        arch/x86/kernel/cpu/mtrr/main.c
        arch/x86/kernel/process.c
        arch/x86/mm/gup.c
        arch/x86/xen/Kconfig
        arch/x86/xen/Makefile
        arch/x86/xen/enlighten.c
        arch/x86/xen/mmu.c
        arch/x86/xen/setup.c
        arch/x86/xen/xen-ops.h
        drivers/block/Kconfig
        drivers/char/hvc_xen.c
        drivers/xen/Kconfig
        drivers/xen/Makefile
        drivers/xen/biomerge.c
        drivers/xen/blkback/Makefile
        drivers/xen/blkback/blkback.c
        drivers/xen/blkback/common.h
        drivers/xen/blkback/vbd.c
        drivers/xen/blkback/xenbus.c
        drivers/xen/events.c
        drivers/xen/xenbus/xenbus_probe.c
        drivers/xen/xenbus/xenbus_probe.h
        drivers/xen/xenbus/xenbus_probe_backend.c
        drivers/xen/xenbus/xenbus_probe_frontend.c
        include/linux/mm.h
        include/xen/blkif.h
        include/xen/events.h
        include/xen/grant_table.h
        include/xen/interface/memory.h

Re: Merging xen/dom0/backend/blktap2 ..

[Ian Campbell]

On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> is an overall pita and I've had the pleasure several times now.

Merging it into what? xen/stable-2.6.32.x or some newer upstream version
based tree?

It appears that xen/stable-2.6.32.x is up to date wrt
xen/dom0/backend/blktap2...

Ian.

> There's a bunch of deltas at the very bottom which look to me like
> unrelated arch stuff which never made it anywhere else. Additional stuff
> which was obsoleted/deprecated (e.g. the pte zapping changes) but
> apparently never reverted.  Plus some xen-related hunks nobody would
> dare to admit to ever have seen before (iirc we had such a thread a
> while ago).
> 
> After a lengthy checkout/--patch orgy, the compound diff looks quite
> simple, in contrast.
> 
> My hope is one could either either revert a whole lot in there (does
> this help reliably during merges? I guess it would). Or, maybe helpful
> in order order to further reduce noise, rebase that tree on some more
> solid root. Dropping quite a bit of garbage here and there. Then call
> that a new branch and phase out the old one.
> 
> >From what I've tried so far, git seems to be reasonably smart about
> remerging such stuff again later. Then again, just reverting might help
> cleaning up elsewhere.
> 
> Preferences? Are there better ways? Or rather just keep it the way it
> is?
> 
> Thanks,
> Daniel
> 
>     Conflicts:
>         arch/x86/include/asm/io.h
>         arch/x86/include/asm/paravirt.h
>         arch/x86/include/asm/xen/page.h
>         arch/x86/kernel/cpu/mtrr/amd.c
>         arch/x86/kernel/cpu/mtrr/centaur.c
>         arch/x86/kernel/cpu/mtrr/cyrix.c
>         arch/x86/kernel/cpu/mtrr/generic.c
>         arch/x86/kernel/cpu/mtrr/main.c
>         arch/x86/kernel/process.c
>         arch/x86/mm/gup.c
>         arch/x86/xen/Kconfig
>         arch/x86/xen/Makefile
>         arch/x86/xen/enlighten.c
>         arch/x86/xen/mmu.c
>         arch/x86/xen/setup.c
>         arch/x86/xen/xen-ops.h
>         drivers/block/Kconfig
>         drivers/char/hvc_xen.c
>         drivers/xen/Kconfig
>         drivers/xen/Makefile
>         drivers/xen/biomerge.c
>         drivers/xen/blkback/Makefile
>         drivers/xen/blkback/blkback.c
>         drivers/xen/blkback/common.h
>         drivers/xen/blkback/vbd.c
>         drivers/xen/blkback/xenbus.c
>         drivers/xen/events.c
>         drivers/xen/xenbus/xenbus_probe.c
>         drivers/xen/xenbus/xenbus_probe.h
>         drivers/xen/xenbus/xenbus_probe_backend.c
>         drivers/xen/xenbus/xenbus_probe_frontend.c
>         include/linux/mm.h
>         include/xen/blkif.h
>         include/xen/events.h
>         include/xen/grant_table.h
>         include/xen/interface/memory.h
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > is an overall pita and I've had the pleasure several times now.
> 
> Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> based tree?

Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
operation, I was just suprised how much garbage is involved.

> It appears that xen/stable-2.6.32.x is up to date wrt
> xen/dom0/backend/blktap2...
> 
> Ian.
> 
> > There's a bunch of deltas at the very bottom which look to me like
> > unrelated arch stuff which never made it anywhere else. Additional stuff
> > which was obsoleted/deprecated (e.g. the pte zapping changes) but
> > apparently never reverted.  Plus some xen-related hunks nobody would
> > dare to admit to ever have seen before (iirc we had such a thread a
> > while ago).
> > 
> > After a lengthy checkout/--patch orgy, the compound diff looks quite
> > simple, in contrast.
> > 
> > My hope is one could either either revert a whole lot in there (does
> > this help reliably during merges? I guess it would). Or, maybe helpful
> > in order order to further reduce noise, rebase that tree on some more
> > solid root. Dropping quite a bit of garbage here and there. Then call
> > that a new branch and phase out the old one.
> > 
> > >From what I've tried so far, git seems to be reasonably smart about
> > remerging such stuff again later. Then again, just reverting might help
> > cleaning up elsewhere.
> > 
> > Preferences? Are there better ways? Or rather just keep it the way it
> > is?
> > 
> > Thanks,
> > Daniel
> > 
> >     Conflicts:
> >         arch/x86/include/asm/io.h
> >         arch/x86/include/asm/paravirt.h
> >         arch/x86/include/asm/xen/page.h
> >         arch/x86/kernel/cpu/mtrr/amd.c
> >         arch/x86/kernel/cpu/mtrr/centaur.c
> >         arch/x86/kernel/cpu/mtrr/cyrix.c
> >         arch/x86/kernel/cpu/mtrr/generic.c
> >         arch/x86/kernel/cpu/mtrr/main.c
> >         arch/x86/kernel/process.c
> >         arch/x86/mm/gup.c
> >         arch/x86/xen/Kconfig
> >         arch/x86/xen/Makefile
> >         arch/x86/xen/enlighten.c
> >         arch/x86/xen/mmu.c
> >         arch/x86/xen/setup.c
> >         arch/x86/xen/xen-ops.h
> >         drivers/block/Kconfig
> >         drivers/char/hvc_xen.c
> >         drivers/xen/Kconfig
> >         drivers/xen/Makefile
> >         drivers/xen/biomerge.c
> >         drivers/xen/blkback/Makefile
> >         drivers/xen/blkback/blkback.c
> >         drivers/xen/blkback/common.h
> >         drivers/xen/blkback/vbd.c
> >         drivers/xen/blkback/xenbus.c
> >         drivers/xen/events.c
> >         drivers/xen/xenbus/xenbus_probe.c
> >         drivers/xen/xenbus/xenbus_probe.h
> >         drivers/xen/xenbus/xenbus_probe_backend.c
> >         drivers/xen/xenbus/xenbus_probe_frontend.c
> >         include/linux/mm.h
> >         include/xen/blkif.h
> >         include/xen/events.h
> >         include/xen/grant_table.h
> >         include/xen/interface/memory.h
> > 
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
> 
> 

Re: Merging xen/dom0/backend/blktap2 ..

[Konrad Rzeszutek Wilk]

On Thu, Mar 10, 2011 at 02:39:47AM -0800, Daniel Stodden wrote:
> On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> > On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > > is an overall pita and I've had the pleasure several times now.
> > 
> > Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> > based tree?
> 
> Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> operation, I was just suprised how much garbage is involved.

There is another party that is interested in doing this too, so it might
be a good idea to compare ideas. Let me ping them to see where they are.

But putting aside the blktap2 driver - what about that ugly #ifdef CONFIG_XEN
piece of code that went in the generic code. Is that gone?

I would think that the first path would be to post patches that introduce
the required infrastructure. For that thought you might want to wait when
the merge window opens and Linus starts pulling Stefano's and my tree. At that point
a lot of the infrastructure backends should be in. Or if you like, you can
take a merge of my #linux-next and Stefano's #linux-next and use that as a base.

I've also up-ported blkback to 2.6.38 - look in devel/xen-blkback-v1 to
see what I needed to do use the M2P/P2M override mechanism.

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Thu, 2011-03-10 at 13:24 -0500, Konrad Rzeszutek Wilk wrote:
> On Thu, Mar 10, 2011 at 02:39:47AM -0800, Daniel Stodden wrote:
> > On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> > > On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > > > is an overall pita and I've had the pleasure several times now.
> > > 
> > > Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> > > based tree?
> > 
> > Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> > operation, I was just suprised how much garbage is involved.
> 
> There is another party that is interested in doing this too, so it might
> be a good idea to compare ideas. Let me ping them to see where they are.
> 
> But putting aside the blktap2 driver - what about that ugly #ifdef CONFIG_XEN
> piece of code that went in the generic code. Is that gone?

??

> I would think that the first path would be to post patches that introduce
> the required infrastructure. 

You mean for blktap? There isn't much infrastructure left, except a
popular zap_page_range export because it doesn't tear down VMAs, just
ptes, to complete requests.

I usually try not to not lose history, so just folding that branch (I
guess the drivers/block transition is an obvious start point) would not
be my preferred solution. But if people prefer that, that's certainly
easy to produce.

> For that thought you might want to wait when
> the merge window opens and Linus starts pulling Stefano's and my tree. At that point
> a lot of the infrastructure backends should be in. Or if you like, you can
> take a merge of my #linux-next and Stefano's #linux-next and use that as a base.
> 
> I've also up-ported blkback to 2.6.38 - look in devel/xen-blkback-v1 to
> see what I needed to do use the   override mechanism.

I found these commits all picked from your devel/next-2.6.38 tree, so
I'm presently still sticking to that. Yup, going  to check out the
override stuff too.

Thanks,
Daniel

Re: Merging xen/dom0/backend/blktap2 ..

[Konrad Rzeszutek Wilk]

On Thu, Mar 10, 2011 at 01:57:53PM -0800, Daniel Stodden wrote:
> On Thu, 2011-03-10 at 13:24 -0500, Konrad Rzeszutek Wilk wrote:
> > On Thu, Mar 10, 2011 at 02:39:47AM -0800, Daniel Stodden wrote:
> > > On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> > > > On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > > > > is an overall pita and I've had the pleasure several times now.
> > > > 
> > > > Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> > > > based tree?
> > > 
> > > Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> > > operation, I was just suprised how much garbage is involved.
> > 
> > There is another party that is interested in doing this too, so it might
> > be a good idea to compare ideas. Let me ping them to see where they are.
> > 
> > But putting aside the blktap2 driver - what about that ugly #ifdef CONFIG_XEN
> > piece of code that went in the generic code. Is that gone?
> 
> ??
e5dd9ae013a75881f9d08b1a2e06250b3ff83408

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Fri, 2011-03-11 at 14:35 -0500, Konrad Rzeszutek Wilk wrote:
> On Thu, Mar 10, 2011 at 01:57:53PM -0800, Daniel Stodden wrote:
> > On Thu, 2011-03-10 at 13:24 -0500, Konrad Rzeszutek Wilk wrote:
> > > On Thu, Mar 10, 2011 at 02:39:47AM -0800, Daniel Stodden wrote:
> > > > On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> > > > > On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > > > > > is an overall pita and I've had the pleasure several times now.
> > > > > 
> > > > > Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> > > > > based tree?
> > > > 
> > > > Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> > > > operation, I was just suprised how much garbage is involved.
> > > 
> > > There is another party that is interested in doing this too, so it might
> > > be a good idea to compare ideas. Let me ping them to see where they are.
> > > 
> > > But putting aside the blktap2 driver - what about that ugly #ifdef CONFIG_XEN
> > > piece of code that went in the generic code. Is that gone?
> > 
> > ??
> e5dd9ae013a75881f9d08b1a2e06250b3ff83408

Oh, VM_FOREIGN. Used to matter for blktap1, and iirc on arch-xen kernels
there (used to) be gntdev code around doing it too. It used to realize
gup() on foreign frames, that's what the M2P override system should have
replaced by now.

Daniel

Merging xen/dom0/backend/blktap2 ..

[Thomas Goetz]

On Mar 10, 2011, at 1:39 PM, xen-devel-request@lists.xensource.com wrote:
> 
> Message: 6
> Date: Thu, 10 Mar 2011 13:24:35 -0500
> From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Subject: Re: [Xen-devel] Merging xen/dom0/backend/blktap2  ..
> To: Daniel Stodden <daniel.stodden@citrix.com>
> Cc: Ian Campbell <Ian.Campbell@eu.citrix.com>,	Jeremy Fitzhardinge
> 	<jeremy@goop.org>,	"xen-devel@lists.xensource.com"
> 	<xen-devel@lists.xensource.com>
> Message-ID: <20110310182435.GB7729@dumpdata.com>
> Content-Type: text/plain; charset=us-ascii
> 
> On Thu, Mar 10, 2011 at 02:39:47AM -0800, Daniel Stodden wrote:
>> On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
>>> On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
>>>> is an overall pita and I've had the pleasure several times now.
>>> 
>>> Merging it into what? xen/stable-2.6.32.x or some newer upstream version
>>> based tree?
>> 
>> Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
>> operation, I was just suprised how much garbage is involved.
> 
> There is another party that is interested in doing this too, so it might
> be a good idea to compare ideas. Let me ping them to see where they are.
> 
> But putting aside the blktap2 driver - what about that ugly #ifdef CONFIG_XEN
> piece of code that went in the generic code. Is that gone?
> 
> I would think that the first path would be to post patches that introduce
> the required infrastructure. For that thought you might want to wait when
> the merge window opens and Linus starts pulling Stefano's and my tree. At that point
> a lot of the infrastructure backends should be in. Or if you like, you can
> take a merge of my #linux-next and Stefano's #linux-next and use that as a base.
> 
> I've also up-ported blkback to 2.6.38 - look in devel/xen-blkback-v1 to
> see what I needed to do use the M2P/P2M override mechanism.
> 
> 

Konrad may be referring to me. I'm working on merging blktap2 into his stable/next-2.6.38 tree. I have Dom0 loopback working and have started on the foreign pages case. I have a PV linux guest coming up reading it's partition table and filesystem, then crashing. I've done this by putting the VM_FORIEGN bit back in. I plan to replace that with something more suitable to PVOPs once it is up and working.


---
Tom Goetz
tcgoetz@gmail.com

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Mon, 2011-03-14 at 08:29 -0400, Thomas Goetz wrote:
> On Mar 10, 2011, at 1:39 PM, xen-devel-request@lists.xensource.com wrote:
> > 
> > Message: 6
> > Date: Thu, 10 Mar 2011 13:24:35 -0500
> > From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > Subject: Re: [Xen-devel] Merging xen/dom0/backend/blktap2  ..
> > To: Daniel Stodden <daniel.stodden@citrix.com>
> > Cc: Ian Campbell <Ian.Campbell@eu.citrix.com>,	Jeremy Fitzhardinge
> > 	<jeremy@goop.org>,	"xen-devel@lists.xensource.com"
> > 	<xen-devel@lists.xensource.com>
> > Message-ID: <20110310182435.GB7729@dumpdata.com>
> > Content-Type: text/plain; charset=us-ascii
> > 
> > On Thu, Mar 10, 2011 at 02:39:47AM -0800, Daniel Stodden wrote:
> >> On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> >>> On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> >>>> is an overall pita and I've had the pleasure several times now.
> >>> 
> >>> Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> >>> based tree?
> >> 
> >> Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> >> operation, I was just suprised how much garbage is involved.
> > 
> > There is another party that is interested in doing this too, so it might
> > be a good idea to compare ideas. Let me ping them to see where they are.
> > 
> > But putting aside the blktap2 driver - what about that ugly #ifdef CONFIG_XEN
> > piece of code that went in the generic code. Is that gone?
> > 
> > I would think that the first path would be to post patches that introduce
> > the required infrastructure. For that thought you might want to wait when
> > the merge window opens and Linus starts pulling Stefano's and my tree. At that point
> > a lot of the infrastructure backends should be in. Or if you like, you can
> > take a merge of my #linux-next and Stefano's #linux-next and use that as a base.
> > 
> > I've also up-ported blkback to 2.6.38 - look in devel/xen-blkback-v1 to
> > see what I needed to do use the M2P/P2M override mechanism.
> > 
> > 
> 
> Konrad may be referring to me. 

> I'm working on merging blktap2 into his stable/next-2.6.38 tree. 

I got that working fine. Presently rather looking into blkback on top of
that. Want a branch to pull from? It's not for konrad though before we
some decision has been made regarding the merging pain.

> I have Dom0 loopback working and have started on the foreign pages case. 

> I have a PV linux guest coming up reading it's partition table and filesystem, then crashing. 

> I've done this by putting the VM_FORIEGN bit back in. I plan to replace that with something more suitable to PVOPs once it is up and working.

VM_FOREIGN isn't needed. Blktap2 in its current state doesn't make use
of it.

What's your take on the conversation above? Did you try reverting the
stray stuff or think it's preferable to just rebuild that that branch?

Cheers,
Daniel

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Thu, 2011-03-10 at 05:39 -0500, Daniel Stodden wrote:
> On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> > On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > > is an overall pita and I've had the pleasure several times now.
> > 
> > Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> > based tree?
> 
> Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> operation, I was just suprised how much garbage is involved.

After looking at the series, I think reverting on that topic branch
might just risk more issues in trees which already pulled the current
branch, and gathering the right diffs from Jeremy's tree to avoid that
would probably take me longer than it's worth. More time than I can
afford.

Since Konrad already seems to do the same with blkback, I'd like to
propose a reset.

Please check out one of the following trees at
http://xenbits.xensource.com/gitweb/?p=people/dstodden/linux.git;a=summary
git://xenbits.xensource.com/people/dstodden/linux.git

blktap/next-2.6.38
blktap/next-2.6.37
blktap/next-2.6.36
blktap/next-2.6.33
blktap/next-2.6.32

I'd redo xen/dom0/backend/blktap2 and repost the diffs sent around last
week. I wouldn't mind keeping that branch in sync too, assuming it
helps.

Trees above start at v2.6.32, with the transition to
drivers/block/blktap, and moving on with Linus' tree from there on.
Versions chosen above are where forward ports were necessary,
respectively. Only fuzz left is mm/memory.c (export zap_page_range for
modules).

Does this sound acceptable?

Thanks,
Daniel

> > It appears that xen/stable-2.6.32.x is up to date wrt
> > xen/dom0/backend/blktap2...
> > 
> > Ian.
> > 
> > > There's a bunch of deltas at the very bottom which look to me like
> > > unrelated arch stuff which never made it anywhere else. Additional stuff
> > > which was obsoleted/deprecated (e.g. the pte zapping changes) but
> > > apparently never reverted.  Plus some xen-related hunks nobody would
> > > dare to admit to ever have seen before (iirc we had such a thread a
> > > while ago).
> > > 
> > > After a lengthy checkout/--patch orgy, the compound diff looks quite
> > > simple, in contrast.
> > > 
> > > My hope is one could either either revert a whole lot in there (does
> > > this help reliably during merges? I guess it would). Or, maybe helpful
> > > in order order to further reduce noise, rebase that tree on some more
> > > solid root. Dropping quite a bit of garbage here and there. Then call
> > > that a new branch and phase out the old one.
> > > 
> > > >From what I've tried so far, git seems to be reasonably smart about
> > > remerging such stuff again later. Then again, just reverting might help
> > > cleaning up elsewhere.
> > > 
> > > Preferences? Are there better ways? Or rather just keep it the way it
> > > is?
> > > 
> > > Thanks,
> > > Daniel
> > > 
> > >     Conflicts:
> > >         arch/x86/include/asm/io.h
> > >         arch/x86/include/asm/paravirt.h
> > >         arch/x86/include/asm/xen/page.h
> > >         arch/x86/kernel/cpu/mtrr/amd.c
> > >         arch/x86/kernel/cpu/mtrr/centaur.c
> > >         arch/x86/kernel/cpu/mtrr/cyrix.c
> > >         arch/x86/kernel/cpu/mtrr/generic.c
> > >         arch/x86/kernel/cpu/mtrr/main.c
> > >         arch/x86/kernel/process.c
> > >         arch/x86/mm/gup.c
> > >         arch/x86/xen/Kconfig
> > >         arch/x86/xen/Makefile
> > >         arch/x86/xen/enlighten.c
> > >         arch/x86/xen/mmu.c
> > >         arch/x86/xen/setup.c
> > >         arch/x86/xen/xen-ops.h
> > >         drivers/block/Kconfig
> > >         drivers/char/hvc_xen.c
> > >         drivers/xen/Kconfig
> > >         drivers/xen/Makefile
> > >         drivers/xen/biomerge.c
> > >         drivers/xen/blkback/Makefile
> > >         drivers/xen/blkback/blkback.c
> > >         drivers/xen/blkback/common.h
> > >         drivers/xen/blkback/vbd.c
> > >         drivers/xen/blkback/xenbus.c
> > >         drivers/xen/events.c
> > >         drivers/xen/xenbus/xenbus_probe.c
> > >         drivers/xen/xenbus/xenbus_probe.h
> > >         drivers/xen/xenbus/xenbus_probe_backend.c
> > >         drivers/xen/xenbus/xenbus_probe_frontend.c
> > >         include/linux/mm.h
> > >         include/xen/blkif.h
> > >         include/xen/events.h
> > >         include/xen/grant_table.h
> > >         include/xen/interface/memory.h
> > > 
> > > 
> > > 
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@lists.xensource.com
> > > http://lists.xensource.com/xen-devel
> > 
> > 
> 
> 

Re: Merging xen/dom0/backend/blktap2 ..

[Konrad Rzeszutek Wilk]

On Tue, Mar 15, 2011 at 05:44:06AM -0700, Daniel Stodden wrote:
> On Thu, 2011-03-10 at 05:39 -0500, Daniel Stodden wrote:
> > On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> > > On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > > > is an overall pita and I've had the pleasure several times now.
> > > 
> > > Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> > > based tree?
> > 
> > Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> > operation, I was just suprised how much garbage is involved.
> 
> After looking at the series, I think reverting on that topic branch
> might just risk more issues in trees which already pulled the current
> branch, and gathering the right diffs from Jeremy's tree to avoid that
> would probably take me longer than it's worth. More time than I can
> afford.
> 
> Since Konrad already seems to do the same with blkback, I'd like to
> propose a reset.
> 
> Please check out one of the following trees at
> http://xenbits.xensource.com/gitweb/?p=people/dstodden/linux.git;a=summary
> git://xenbits.xensource.com/people/dstodden/linux.git
> 
> blktap/next-2.6.38
> blktap/next-2.6.37
> blktap/next-2.6.36
> blktap/next-2.6.33
> blktap/next-2.6.32
> 
> I'd redo xen/dom0/backend/blktap2 and repost the diffs sent around last
> week. I wouldn't mind keeping that branch in sync too, assuming it
> helps.
> 
> Trees above start at v2.6.32, with the transition to
> drivers/block/blktap, and moving on with Linus' tree from there on.
> Versions chosen above are where forward ports were necessary,
> respectively. Only fuzz left is mm/memory.c (export zap_page_range for
> modules).

Can you make a different branch (or just send me the git commit)
for the one that touches mm/memory.c?

> 
> Does this sound acceptable?

I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
merge tree. Can you make a tree that is based off 2.6.38 (or some
branch of my 'stable/' ones). Basically trying to have something that is
easy to merge and is self-containted within one branch.

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Tue, 2011-03-15 at 15:53 -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Mar 15, 2011 at 05:44:06AM -0700, Daniel Stodden wrote:
> > On Thu, 2011-03-10 at 05:39 -0500, Daniel Stodden wrote:
> > > On Thu, 2011-03-10 at 03:31 -0500, Ian Campbell wrote:
> > > > On Thu, 2011-03-10 at 03:33 +0000, Daniel Stodden wrote:
> > > > > is an overall pita and I've had the pleasure several times now.
> > > > 
> > > > Merging it into what? xen/stable-2.6.32.x or some newer upstream version
> > > > based tree?
> > > 
> > > Newer upstream. Otherwise I wouldn't bother. It's certainly not a common
> > > operation, I was just suprised how much garbage is involved.
> > 
> > After looking at the series, I think reverting on that topic branch
> > might just risk more issues in trees which already pulled the current
> > branch, and gathering the right diffs from Jeremy's tree to avoid that
> > would probably take me longer than it's worth. More time than I can
> > afford.
> > 
> > Since Konrad already seems to do the same with blkback, I'd like to
> > propose a reset.
> > 
> > Please check out one of the following trees at
> > http://xenbits.xensource.com/gitweb/?p=people/dstodden/linux.git;a=summary
> > git://xenbits.xensource.com/people/dstodden/linux.git
> > 
> > blktap/next-2.6.38
> > blktap/next-2.6.37
> > blktap/next-2.6.36
> > blktap/next-2.6.33
> > blktap/next-2.6.32
> > 
> > I'd redo xen/dom0/backend/blktap2 and repost the diffs sent around last
> > week. I wouldn't mind keeping that branch in sync too, assuming it
> > helps.
> > 
> > Trees above start at v2.6.32, with the transition to
> > drivers/block/blktap, and moving on with Linus' tree from there on.
> > Versions chosen above are where forward ports were necessary,
> > respectively. Only fuzz left is mm/memory.c (export zap_page_range for
> > modules).
> 
> Can you make a different branch (or just send me the git commit)
> for the one that touches mm/memory.c?

That's the initial one: 7ccd87f. You could strip that but it's not going
to build as a module before that ref is gone. It might go at some point.

> > 
> > Does this sound acceptable?
> 
> I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
> merge tree. Can you make a tree that is based off 2.6.38 (or some
> branch of my 'stable/' ones). Basically trying to have something that is
> easy to merge and is self-containted within one branch.

It is rooted on 2.6.32 and incrementally moves on up to currently
v2.6.38, no stray diffs except the forward porting where needed. There's
at least one conflict resolution in Kconfig around 36 or 37, iirc. Any
later kernel will look more or less the same.

$ git list xenbits/blktap/next-2.6.38 ^v2.6.38
eb8040c Merge commit 'v2.6.38' into blktap/next-2.6.38
bf926e6 blktap: Forward port to 2.6.37
9f65e90 Merge commit 'v2.6.37' into blktap/next-2.6.37
7ef4e35 blktap: Forward port to 2.6.36
a55f064 Merge commit 'v2.6.36' into blktap/next-2.6.36
994a546 blktap: Add discard queue limits.
ea2d7e7 Merge blktap into blktap/next-2.6.33
e37d737 blktap: Add BLKTAP_OP_TRIM command option.
42276df blktap: Add BLKTAP_OP_FLUSH command option.
5d10876 blktap: Add physical sector device info.
8169b25 blktap: Drop the ring message timestamp.
34574a8 blktap: Support non-R/W requests
a765257 blktap: Fix reference to freed struct request.
7ccd87f blktap: Blktap userspace devices.

You could rebase it on v2.6.38 if you want to reproduce the merging and
mangle commits, although I'm not sure why. For the foreseeable future,
I'd like to keep 2.6.32 and anything later going, so that repo will get
incoming stuff at 2.6.32 and, where possible, I'd expect the greater
kernels to typically just fast-forward from where they are now.

If you want topic branches: I'm not planning to do those. Mainly because
it's a bad idea. If that entire thing would be about to go upstream with
limited time to land that might a different thing, but it's clearly not
there in its present state.

That acceptable?

Daniel

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Tue, 2011-03-15 at 17:04 -0400, Daniel Stodden wrote:

> > 
> > Can you make a different branch (or just send me the git commit)
> > for the one that touches mm/memory.c?
> 
> That's the initial one: 7ccd87f. You could strip that but it's not going
> to build as a module before that ref is gone. It might go at some point.

Oh. Update: I just noticed there's zap_vma_ptes now. So scratch that.
Amazing, always thought I'd eventually have to tear down vmas.

Cheers,
Daniel

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Tue, 2011-03-15 at 20:43 -0400, Daniel Stodden wrote:
> On Tue, 2011-03-15 at 17:04 -0400, Daniel Stodden wrote:
> 
> > > 
> > > Can you make a different branch (or just send me the git commit)
> > > for the one that touches mm/memory.c?
> > 
> > That's the initial one: 7ccd87f. You could strip that but it's not going
> > to build as a module before that ref is gone. It might go at some point.
> 
> Oh. Update: I just noticed there's zap_vma_ptes now. So scratch that.
> Amazing, always thought I'd eventually have to tear down vmas.

Ooops, PFNMAP only. Sorry...

Re: Merging xen/dom0/backend/blktap2 ..

[Konrad Rzeszutek Wilk]

> > Can you make a different branch (or just send me the git commit)
> > for the one that touches mm/memory.c?
> 
> That's the initial one: 7ccd87f. You could strip that but it's not going
> to build as a module before that ref is gone. It might go at some point.

For upstream we need that as a separate git commit. Otherwise we might
not get MM maintainers Ack-ing the git commit b/c they would have to review
the blktap driver too. Please do split it out in two commits.

> 
> > > 
> > > Does this sound acceptable?
> > 
> > I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
> > merge tree. Can you make a tree that is based off 2.6.38 (or some
> > branch of my 'stable/' ones). Basically trying to have something that is
> > easy to merge and is self-containted within one branch.
> 
> It is rooted on 2.6.32 and incrementally moves on up to currently
> v2.6.38, no stray diffs except the forward porting where needed. There's
> at least one conflict resolution in Kconfig around 36 or 37, iirc. Any
> later kernel will look more or less the same.
> 
> $ git list xenbits/blktap/next-2.6.38 ^v2.6.38
> eb8040c Merge commit 'v2.6.38' into blktap/next-2.6.38
> bf926e6 blktap: Forward port to 2.6.37
> 9f65e90 Merge commit 'v2.6.37' into blktap/next-2.6.37
> 7ef4e35 blktap: Forward port to 2.6.36
> a55f064 Merge commit 'v2.6.36' into blktap/next-2.6.36
> 994a546 blktap: Add discard queue limits.
> ea2d7e7 Merge blktap into blktap/next-2.6.33
> e37d737 blktap: Add BLKTAP_OP_TRIM command option.
> 42276df blktap: Add BLKTAP_OP_FLUSH command option.
> 5d10876 blktap: Add physical sector device info.
> 8169b25 blktap: Drop the ring message timestamp.
> 34574a8 blktap: Support non-R/W requests
> a765257 blktap: Fix reference to freed struct request.
> 7ccd87f blktap: Blktap userspace devices.
> 
> You could rebase it on v2.6.38 if you want to reproduce the merging and
> mangle commits, although I'm not sure why. For the foreseeable future,
> I'd like to keep 2.6.32 and anything later going, so that repo will get
> incoming stuff at 2.6.32 and, where possible, I'd expect the greater

Ah, ambitious. I tried that with xen-pcifront and had to resort
to making trees for different versions. But this could work for you.

> kernels to typically just fast-forward from where they are now.

The issue is git bisection. The dates on those commits is quite early so
I wonder if somebody did a git bisect whether they would hit those and
end up with compilation issues. Perhaps the first patch should
just introduce the driver, but not touch the Kconfig at all.

And then the last one actually enables the Kconfig. And as you
add updates, you move the patch with Kconfig to be the last one?

> 
> If you want topic branches: I'm not planning to do those. Mainly because
> it's a bad idea. If that entire thing would be about to go upstream with
> limited time to land that might a different thing, but it's clearly not
> there in its present state.

What is a "bad" about it? What do you want to do when the driver is ready
for upstream? You would have to do this topic branch at some point, wouldn't you?
What is a topic branch to you? When I think topic branch I think:
devel/xen-pciback-0.5 for example.

The reason I am asking about this is b/c of my inept git skills. Doing
"git pull daniel/blktap" and just having it fetch patches that are relevant
to blktap makes it soooo much easier to get an idea what is happening. And also
if I need to revert something - but it could be very well me not being
elite with git.

Granted if there are bug fixes for things that aren't in the topic branch
but surface up in a merge branch (example: 2.6.38 + #your tree) I usually just
rebase it on top of 2.6.38 so I can have that patch in and also give that
branch a new name (v3->v4, and so on).

> 
> That acceptable?
> 
> Daniel

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Tue, 2011-03-15 at 23:02 -0400, Konrad Rzeszutek Wilk wrote: 
> > > Can you make a different branch (or just send me the git commit)
> > > for the one that touches mm/memory.c?
> > 
> > That's the initial one: 7ccd87f. You could strip that but it's not going
> > to build as a module before that ref is gone. It might go at some point.
> 
> For upstream we need that as a separate git commit. Otherwise we might
> not get MM maintainers Ack-ing the git commit b/c they would have to review
> the blktap driver too. Please do split it out in two commits.
> 

This piece is not ready for upstream, but you'd be right.

Proposing a zap_page_range export to mm maintainers will produce a
simple "you're doing it wrong", let's not split commits just for that.

My apologies, that detail dates back to the dawn of xen-blktap1.
Userspace is used to mapping a single large VMA, and the driver flips
ptes implicitly as I/O reqs leave and return again. That's machine-wise
not much of a difference, but for normal memory there's mmap/munmap
already, so module code is usually not encouraged to invent funny new VM
area models. Hence, zap_page_range remains private.

Can it just resort to mmap/munmap? Probably, even implicitly from ioctl
context I guess.

If it hopelessly got in your way, one could back it out, the loss is
TAP=m.

> > 
> > > > 
> > > > Does this sound acceptable?
> > > 
> > > I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
> > > merge tree. Can you make a tree that is based off 2.6.38 (or some
> > > branch of my 'stable/' ones). Basically trying to have something that is
> > > easy to merge and is self-containted within one branch.
> > 
> > It is rooted on 2.6.32 and incrementally moves on up to currently
> > v2.6.38, no stray diffs except the forward porting where needed. There's
> > at least one conflict resolution in Kconfig around 36 or 37, iirc. Any
> > later kernel will look more or less the same.
> > 
> > $ git list xenbits/blktap/next-2.6.38 ^v2.6.38
> > eb8040c Merge commit 'v2.6.38' into blktap/next-2.6.38
> > bf926e6 blktap: Forward port to 2.6.37
> > 9f65e90 Merge commit 'v2.6.37' into blktap/next-2.6.37
> > 7ef4e35 blktap: Forward port to 2.6.36
> > a55f064 Merge commit 'v2.6.36' into blktap/next-2.6.36
> > 994a546 blktap: Add discard queue limits.
> > ea2d7e7 Merge blktap into blktap/next-2.6.33
> > e37d737 blktap: Add BLKTAP_OP_TRIM command option.
> > 42276df blktap: Add BLKTAP_OP_FLUSH command option.
> > 5d10876 blktap: Add physical sector device info.
> > 8169b25 blktap: Drop the ring message timestamp.
> > 34574a8 blktap: Support non-R/W requests
> > a765257 blktap: Fix reference to freed struct request.
> > 7ccd87f blktap: Blktap userspace devices.
> > 
> > You could rebase it on v2.6.38 if you want to reproduce the merging and
> > mangle commits, although I'm not sure why. For the foreseeable future,
> > I'd like to keep 2.6.32 and anything later going, so that repo will get
> > incoming stuff at 2.6.32 and, where possible, I'd expect the greater
> 
> Ah, ambitious. I tried that with xen-pcifront and had to resort
> to making trees for different versions. But this could work for you.

But it should work fine here. There's only a single source tree, which
is linux-2.6.git, and only a single component, which aims to yield the
same extensions where possible. Doesn't get much easier than that.

I'd agree that components interfacing with 4 moving xen subsystems, as
in blkback etc. is a bit of a different matter.

Still, killing history altogether can't be the answer.

> > kernels to typically just fast-forward from where they are now.
> 
> The issue is git bisection. The dates on those commits is quite early so
> I wonder if somebody did a git bisect whether they would hit those and
> end up with compilation issues. Perhaps the first patch should
> just introduce the driver, but not touch the Kconfig at all.
> 
> And then the last one actually enables the Kconfig. And as you
> add updates, you move the patch with Kconfig to be the last one?
> 
> > 
> > If you want topic branches: I'm not planning to do those. Mainly because
> > it's a bad idea. If that entire thing would be about to go upstream with
> > limited time to land that might a different thing, but it's clearly not
> > there in its present state.
> 
> What is a "bad" about it? What do you want to do when the driver is ready
> for upstream? You would have to do this topic branch at some point, wouldn't you?
> What is a topic branch to you? When I think topic branch I think:
> devel/xen-pciback-0.5 for example.

When (iff) that driver gets ready for upstream I guess it'd have to be
folded down and optionally split, pretty much exactly as you describe.

This is my third attempt to write a proper response to your concerns,
because so far I'm not super-experienced with git either.

I was going to disagree because keeping separate queues is a bit of a
workflow killer.

Then I was going to agree because commit atomicity for proper bisection
is a actually pretty good point, imho.

The thing I hate about rebasing/cherry-picking is not even the extra
work, it's that the dupes mean one loses any kind of traction wrt what's
in a particular derived tree and not. So in order to be able to compare
two such branches one has to diff sources, git-blame, and understanding
a whole lot too much about the content.

The commit atomicity issue could be solved by making sure stay in a
branch, and only get merged, not pulled through by fast-forward. That
git-merge --no-ff option looks like it was meant to ensure that.

There's another way to make stuff atomic: Amending merges with the
following port. A git-commit --amend can do that. Took me ages to find
that out, because for reasons unclear, git-rebase -i alone (as 'fixup'
changes) can't.

I tried whether that's better. Can't recommend it. Git appears to have a
really hard time turning such ports/merges back into diffs, and having
those diffs is quite useful. It's not impossible, but format-patch alone
can't, which gets a bit counterintuitive.

> The reason I am asking about this is b/c of my inept git skills. Doing
> "git pull daniel/blktap" and just having it fetch patches that are relevant
> to blktap makes it soooo much easier to get an idea what is happening.

Well, it's not like it's going to pull garbage. These are all blktap
exclusively, rooted at v2.6.38. Just not ported individually, but in
piles.

Let's assume one would go through the pain to port those one after one,
by cherry-picking and careful rebuild. With 2.6.39 one had to start over
again, porting every commit once again, and making sure it compiles to
stay consistent, again for bisection purposes. And so on, every couple
months at least.

That continues, until this thing gets either dropped or upstreamed, at
which time an O(n*m) disaster gets folded down and discarded, one way or
the other. That not very efficient.

The reality is it looks like git can't deal with it any better that what
I got there.

So I'd rather ask you open a konrad/blktap-2.6.38, tracking that branch,
and carefully merge that in, in a way not risking bisection.

If that's okay, next question would probably be if one shouldn't try do
the same with blkback >:)

Cheers,
Daniel 

Re: Merging xen/dom0/backend/blktap2 ..

[Konrad Rzeszutek Wilk]

On Sat, Mar 19, 2011 at 04:20:45PM -0700, Daniel Stodden wrote:
> On Tue, 2011-03-15 at 23:02 -0400, Konrad Rzeszutek Wilk wrote: 
> > > > Can you make a different branch (or just send me the git commit)
> > > > for the one that touches mm/memory.c?
> > > 
> > > That's the initial one: 7ccd87f. You could strip that but it's not going
> > > to build as a module before that ref is gone. It might go at some point.
> > 
> > For upstream we need that as a separate git commit. Otherwise we might
> > not get MM maintainers Ack-ing the git commit b/c they would have to review
> > the blktap driver too. Please do split it out in two commits.
> > 
> 
> This piece is not ready for upstream, but you'd be right.
> 
> Proposing a zap_page_range export to mm maintainers will produce a
> simple "you're doing it wrong", let's not split commits just for that.
> 
> My apologies, that detail dates back to the dawn of xen-blktap1.
> Userspace is used to mapping a single large VMA, and the driver flips
> ptes implicitly as I/O reqs leave and return again. That's machine-wise
> not much of a difference, but for normal memory there's mmap/munmap
> already, so module code is usually not encouraged to invent funny new VM
> area models. Hence, zap_page_range remains private.
> 
> Can it just resort to mmap/munmap? Probably, even implicitly from ioctl
> context I guess.

The gntdev solved this by clearing the PTE on unmap (using the gnttab API and
the M2P/P2M override which clears the PTE).

Would that work?
> 
> If it hopelessly got in your way, one could back it out, the loss is
> TAP=m.
> 
> > > 
> > > > > 
> > > > > Does this sound acceptable?
> > > > 
> > > > I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
> > > > merge tree. Can you make a tree that is based off 2.6.38 (or some
> > > > branch of my 'stable/' ones). Basically trying to have something that is
> > > > easy to merge and is self-containted within one branch.
> > > 
> > > It is rooted on 2.6.32 and incrementally moves on up to currently
> > > v2.6.38, no stray diffs except the forward porting where needed. There's
> > > at least one conflict resolution in Kconfig around 36 or 37, iirc. Any
> > > later kernel will look more or less the same.
> > > 
> > > $ git list xenbits/blktap/next-2.6.38 ^v2.6.38
> > > eb8040c Merge commit 'v2.6.38' into blktap/next-2.6.38
> > > bf926e6 blktap: Forward port to 2.6.37
> > > 9f65e90 Merge commit 'v2.6.37' into blktap/next-2.6.37
> > > 7ef4e35 blktap: Forward port to 2.6.36
> > > a55f064 Merge commit 'v2.6.36' into blktap/next-2.6.36
> > > 994a546 blktap: Add discard queue limits.
> > > ea2d7e7 Merge blktap into blktap/next-2.6.33
> > > e37d737 blktap: Add BLKTAP_OP_TRIM command option.
> > > 42276df blktap: Add BLKTAP_OP_FLUSH command option.
> > > 5d10876 blktap: Add physical sector device info.
> > > 8169b25 blktap: Drop the ring message timestamp.
> > > 34574a8 blktap: Support non-R/W requests
> > > a765257 blktap: Fix reference to freed struct request.
> > > 7ccd87f blktap: Blktap userspace devices.
> > > 
> > > You could rebase it on v2.6.38 if you want to reproduce the merging and
> > > mangle commits, although I'm not sure why. For the foreseeable future,
> > > I'd like to keep 2.6.32 and anything later going, so that repo will get
> > > incoming stuff at 2.6.32 and, where possible, I'd expect the greater
> > 
> > Ah, ambitious. I tried that with xen-pcifront and had to resort
> > to making trees for different versions. But this could work for you.
> 
> But it should work fine here. There's only a single source tree, which
> is linux-2.6.git, and only a single component, which aims to yield the
> same extensions where possible. Doesn't get much easier than that.
> 
> I'd agree that components interfacing with 4 moving xen subsystems, as
> in blkback etc. is a bit of a different matter.
> 
> Still, killing history altogether can't be the answer.

Seems to be the answer nowadays. David Miller asked Ian to squash the full
history in one commit, and provide a "historic" git tree where all of the
git commits reside.

> 
> > > kernels to typically just fast-forward from where they are now.
> > 
> > The issue is git bisection. The dates on those commits is quite early so
> > I wonder if somebody did a git bisect whether they would hit those and
> > end up with compilation issues. Perhaps the first patch should
> > just introduce the driver, but not touch the Kconfig at all.
> > 
> > And then the last one actually enables the Kconfig. And as you
> > add updates, you move the patch with Kconfig to be the last one?
> > 
> > > 
> > > If you want topic branches: I'm not planning to do those. Mainly because
> > > it's a bad idea. If that entire thing would be about to go upstream with
> > > limited time to land that might a different thing, but it's clearly not
> > > there in its present state.
> > 
> > What is a "bad" about it? What do you want to do when the driver is ready
> > for upstream? You would have to do this topic branch at some point, wouldn't you?
> > What is a topic branch to you? When I think topic branch I think:
> > devel/xen-pciback-0.5 for example.
> 
> When (iff) that driver gets ready for upstream I guess it'd have to be
> folded down and optionally split, pretty much exactly as you describe.
> 
> This is my third attempt to write a proper response to your concerns,
> because so far I'm not super-experienced with git either.
> 
> I was going to disagree because keeping separate queues is a bit of a
> workflow killer.
> 
> Then I was going to agree because commit atomicity for proper bisection
> is a actually pretty good point, imho.
> 
> The thing I hate about rebasing/cherry-picking is not even the extra
> work, it's that the dupes mean one loses any kind of traction wrt what's
> in a particular derived tree and not. So in order to be able to compare
> two such branches one has to diff sources, git-blame, and understanding
> a whole lot too much about the content.

Or:
git shortlog devel/xen-pciback-0.3..devel/xen-pciback-0.5  --grep="pciback"

Which gives you some good idea of what was added... that is if one
does not mess with the git commits and amend them (which I sometimes too
since they are still "devel").

> 
> The commit atomicity issue could be solved by making sure stay in a
> branch, and only get merged, not pulled through by fast-forward. That
> git-merge --no-ff option looks like it was meant to ensure that.
> 
> There's another way to make stuff atomic: Amending merges with the
> following port. A git-commit --amend can do that. Took me ages to find
> that out, because for reasons unclear, git-rebase -i alone (as 'fixup'
> changes) can't.
> 
> I tried whether that's better. Can't recommend it. Git appears to have a
> really hard time turning such ports/merges back into diffs, and having
> those diffs is quite useful. It's not impossible, but format-patch alone
> can't, which gets a bit counterintuitive.
> 
> > The reason I am asking about this is b/c of my inept git skills. Doing
> > "git pull daniel/blktap" and just having it fetch patches that are relevant
> > to blktap makes it soooo much easier to get an idea what is happening.
> 
> Well, it's not like it's going to pull garbage. These are all blktap
> exclusively, rooted at v2.6.38. Just not ported individually, but in
> piles.

OK. The desciption were a bit generic: "porting to 2.6.37" .. doesn't really
tell what you had to do, or what not. I did not look in the description, so
it might have had the details.

> 
> Let's assume one would go through the pain to port those one after one,
> by cherry-picking and careful rebuild. With 2.6.39 one had to start over
> again, porting every commit once again, and making sure it compiles to
> stay consistent, again for bisection purposes. And so on, every couple
> months at least.

That can be automated quite easily. The .git/hooks can do the make process
automatic before checking it, and failing if it is not working.

So once you set that up, it is as simple as 'git rebase -i v2.6.39'...
but I am not sure if that is needed.

The reason you might need to rebase it is if the newer tree has thrown some
API out or introduced a new one that the blktap can use. But if that is
not the case, there should be no trouble on a 2.6.40 tree to do:

git merge <devel-tree-based-on-2.6.36> .. and fix up the little merge
issues (if any).

> 
> That continues, until this thing gets either dropped or upstreamed, at
> which time an O(n*m) disaster gets folded down and discarded, one way or
> the other. That not very efficient.

The whole upstream effort is not efficient at all :-) It sometimes
is akin to trying to convience a tax auditor that they are wrong.

> 
> The reality is it looks like git can't deal with it any better that what
> I got there.
> 
> So I'd rather ask you open a konrad/blktap-2.6.38, tracking that branch,
> and carefully merge that in, in a way not risking bisection.

OK. Bisection is important - especially during those rc-X cycles where
stuff stops working and is a tangle to figure out what went wrong.

And it sounds to me that you want to defeer the idea of upstreaming
for some time, and when you are comfortable with blktap2 being in great
shape - then start the process.

When it comes to upstreaming process the fashion looks to post one
nice patch that includes the driver. Infrastructure patches should be
done as seperate patches. So at that point it probably won't matter
at all whether you have little bits of patches, or just one big one.
The maintainer (Jens Axboe) will probably just pick the big one.

> 
> If that's okay, next question would probably be if one shouldn't try do
> the same with blkback >:)

For authorship I prefer to keep branches. So say I post the blbkback
driver "as is" for review. People come back with reviews, or what not - I create
a new branch with a new patch with the review feedback. That way when
I am finally done, I've this "historic" branch that has all the names of
people who contributed to it.

There is a twist to all of this. Linus himself prefers to ingest whole
git branches. Other maintainers, like just one single patch.

Let me ping Jens Axboe and find out what he prefers. That should
give us a good idea of where to continue.

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Sun, 2011-03-20 at 16:28 -0400, Konrad Rzeszutek Wilk wrote:

> > Proposing a zap_page_range export to mm maintainers will produce a
> > simple "you're doing it wrong", let's not split commits just for that.
> > 
> > My apologies, that detail dates back to the dawn of xen-blktap1.
> > Userspace is used to mapping a single large VMA, and the driver flips
> > ptes implicitly as I/O reqs leave and return again. That's machine-wise
> > not much of a difference, but for normal memory there's mmap/munmap
> > already, so module code is usually not encouraged to invent funny new VM
> > area models. Hence, zap_page_range remains private.
> > 
> > Can it just resort to mmap/munmap? Probably, even implicitly from ioctl
> > context I guess.
> 
> The gntdev solved this by clearing the PTE on unmap (using the gnttab API and
> the M2P/P2M override which clears the PTE).
> 
> Would that work?

Well, gntdev gets a normal munmap() from userland when it's time to tear
down the VMA. That always works, it's how it's meant to be. It's more of
a challenge for funny PTE types like foreign memory, but I guess that's
solved now. The latter is not even the case here.

> > If it hopelessly got in your way, one could back it out, the loss is
> > TAP=m.
> > 
> > > > 
> > > > > > 
> > > > > > Does this sound acceptable?
> > > > > 
> > > > > I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
> > > > > merge tree. Can you make a tree that is based off 2.6.38 (or some
> > > > > branch of my 'stable/' ones). Basically trying to have something that is
> > > > > easy to merge and is self-containted within one branch.
> > > > 
> > > > It is rooted on 2.6.32 and incrementally moves on up to currently
> > > > v2.6.38, no stray diffs except the forward porting where needed. There's
> > > > at least one conflict resolution in Kconfig around 36 or 37, iirc. Any
> > > > later kernel will look more or less the same.
> > > > 
> > > > $ git list xenbits/blktap/next-2.6.38 ^v2.6.38
> > > > eb8040c Merge commit 'v2.6.38' into blktap/next-2.6.38
> > > > bf926e6 blktap: Forward port to 2.6.37
> > > > 9f65e90 Merge commit 'v2.6.37' into blktap/next-2.6.37
> > > > 7ef4e35 blktap: Forward port to 2.6.36
> > > > a55f064 Merge commit 'v2.6.36' into blktap/next-2.6.36
> > > > 994a546 blktap: Add discard queue limits.
> > > > ea2d7e7 Merge blktap into blktap/next-2.6.33
> > > > e37d737 blktap: Add BLKTAP_OP_TRIM command option.
> > > > 42276df blktap: Add BLKTAP_OP_FLUSH command option.
> > > > 5d10876 blktap: Add physical sector device info.
> > > > 8169b25 blktap: Drop the ring message timestamp.
> > > > 34574a8 blktap: Support non-R/W requests
> > > > a765257 blktap: Fix reference to freed struct request.
> > > > 7ccd87f blktap: Blktap userspace devices.
> > > > 
> > > > You could rebase it on v2.6.38 if you want to reproduce the merging and
> > > > mangle commits, although I'm not sure why. For the foreseeable future,
> > > > I'd like to keep 2.6.32 and anything later going, so that repo will get
> > > > incoming stuff at 2.6.32 and, where possible, I'd expect the greater
> > > 
> > > Ah, ambitious. I tried that with xen-pcifront and had to resort
> > > to making trees for different versions. But this could work for you.
> > 
> > But it should work fine here. There's only a single source tree, which
> > is linux-2.6.git, and only a single component, which aims to yield the
> > same extensions where possible. Doesn't get much easier than that.
> > 
> > I'd agree that components interfacing with 4 moving xen subsystems, as
> > in blkback etc. is a bit of a different matter.
> > 
> > Still, killing history altogether can't be the answer.
> 
> Seems to be the answer nowadays. David Miller asked Ian to squash the full
> history in one commit, and provide a "historic" git tree where all of the
> git commits reside.

For an upstream intro, sure. I'd probably ask for the same if I were the
maintainer. No surprise.

>From there on, even merging branches is probably fine again, provided
individual commits don't relate and there's no fix-this/forgot-that
stuff documenting how people got there. Nobody needs that in mainline.

> > 
> > > > kernels to typically just fast-forward from where they are now.
> > > 
> > > The issue is git bisection. The dates on those commits is quite early so
> > > I wonder if somebody did a git bisect whether they would hit those and
> > > end up with compilation issues. Perhaps the first patch should
> > > just introduce the driver, but not touch the Kconfig at all.
> > > 
> > > And then the last one actually enables the Kconfig. And as you
> > > add updates, you move the patch with Kconfig to be the last one?
> > > 
> > > > 
> > > > If you want topic branches: I'm not planning to do those. Mainly because
> > > > it's a bad idea. If that entire thing would be about to go upstream with
> > > > limited time to land that might a different thing, but it's clearly not
> > > > there in its present state.
> > > 
> > > What is a "bad" about it? What do you want to do when the driver is ready
> > > for upstream? You would have to do this topic branch at some point, wouldn't you?
> > > What is a topic branch to you? When I think topic branch I think:
> > > devel/xen-pciback-0.5 for example.
> > 
> > When (iff) that driver gets ready for upstream I guess it'd have to be
> > folded down and optionally split, pretty much exactly as you describe.
> > 
> > This is my third attempt to write a proper response to your concerns,
> > because so far I'm not super-experienced with git either.
> > 
> > I was going to disagree because keeping separate queues is a bit of a
> > workflow killer.
> > 
> > Then I was going to agree because commit atomicity for proper bisection
> > is a actually pretty good point, imho.
> > 
> > The thing I hate about rebasing/cherry-picking is not even the extra
> > work, it's that the dupes mean one loses any kind of traction wrt what's
> > in a particular derived tree and not. So in order to be able to compare
> > two such branches one has to diff sources, git-blame, and understanding
> > a whole lot too much about the content.
> 
> Or:
> git shortlog devel/xen-pciback-0.3..devel/xen-pciback-0.5  --grep="pciback"
> 
> Which gives you some good idea of what was added... that is if one
> does not mess with the git commits and amend them (which I sometimes too
> since they are still "devel").

I'm assuming pciback-0.5 supersedes/deprecates pciback-0.3?

> > The commit atomicity issue could be solved by making sure stay in a
> > branch, and only get merged, not pulled through by fast-forward. That
> > git-merge --no-ff option looks like it was meant to ensure that.
> > 
> > There's another way to make stuff atomic: Amending merges with the
> > following port. A git-commit --amend can do that. Took me ages to find
> > that out, because for reasons unclear, git-rebase -i alone (as 'fixup'
> > changes) can't.
> > 
> > I tried whether that's better. Can't recommend it. Git appears to have a
> > really hard time turning such ports/merges back into diffs, and having
> > those diffs is quite useful. It's not impossible, but format-patch alone
> > can't, which gets a bit counterintuitive.
> > 
> > > The reason I am asking about this is b/c of my inept git skills. Doing
> > > "git pull daniel/blktap" and just having it fetch patches that are relevant
> > > to blktap makes it soooo much easier to get an idea what is happening.
> > 
> > Well, it's not like it's going to pull garbage. These are all blktap
> > exclusively, rooted at v2.6.38. Just not ported individually, but in
> > piles.
> 
> OK. The desciption were a bit generic: "porting to 2.6.37" .. doesn't really
> tell what you had to do, or what not. I did not look in the description, so
> it might have had the details.

There are more details in the commit message. But as far as I can tell,
there's not much point in splitting them any more thoroughly.

> > Let's assume one would go through the pain to port those one after one,
> > by cherry-picking and careful rebuild. With 2.6.39 one had to start over
> > again, porting every commit once again, and making sure it compiles to
> > stay consistent, again for bisection purposes. And so on, every couple
> > months at least.
> 
> That can be automated quite easily. The .git/hooks can do the make process
> automatic before checking it, and failing if it is not working.
>
> So once you set that up, it is as simple as 'git rebase -i v2.6.39'...
> but I am not sure if that is needed.
> 
> The reason you might need to rebase it is if the newer tree has thrown some
> API out or introduced a new one that the blktap can use. But if that is
> not the case, there should be no trouble on a 2.6.40 tree to do:

I'd probably make that another patch on top.

> git merge <devel-tree-based-on-2.6.36> .. and fix up the little merge
> issues (if any).
> 
> > 
> > That continues, until this thing gets either dropped or upstreamed, at
> > which time an O(n*m) disaster gets folded down and discarded, one way or
> > the other. That not very efficient.
> 
> The whole upstream effort is not efficient at all :-) It sometimes
> is akin to trying to convience a tax auditor that they are wrong.

Well yeah. But my concern here, again, is not upstreaming. The problem
is that 2.6.38 is important, but not integral. There's 2.6.32, XCP,
XenClient and all those trees will remain under maintenance. A merge and
forward port is more efficient than rebasing.

> > The reality is it looks like git can't deal with it any better that what
> > I got there.
> > 
> > So I'd rather ask you open a konrad/blktap-2.6.38, tracking that branch,
> > and carefully merge that in, in a way not risking bisection.
> 
> OK. Bisection is important - especially during those rc-X cycles where
> stuff stops working and is a tangle to figure out what went wrong.
> 
> And it sounds to me that you want to defeer the idea of upstreaming
> for some time, and when you are comfortable with blktap2 being in great
> shape - then start the process.

There's more work, and it's far beyond mmap. I'd first have to talk to
people about some of the implications which I can't just fix in there.

The whole blkdev-in-userspace thing looks like an obviously good idea.
Like FUSE. It's been envisioned as just that. But while it works fine
under guests, upstreaming would implicitly promote it to carry host I/O.
Now, in that area, XCP carries a couple extra patches to help dom0 with
provisioning of disk images under memory congestion. You really don't
want to know about those.

> When it comes to upstreaming process the fashion looks to post one
> nice patch that includes the driver. Infrastructure patches should be
> done as seperate patches. So at that point it probably won't matter
> at all whether you have little bits of patches, or just one big one.
> The maintainer (Jens Axboe) will probably just pick the big one.
> 
> > 
> > If that's okay, next question would probably be if one shouldn't try do
> > the same with blkback >:)
> 
> For authorship I prefer to keep branches. So say I post the blbkback
> driver "as is" for review. People come back with reviews, or what not - I create
> a new branch with a new patch with the review feedback. That way when
> I am finally done, I've this "historic" branch that has all the names of
> people who contributed to it.
> 
> There is a twist to all of this. Linus himself prefers to ingest whole
> git branches. Other maintainers, like just one single patch.
> 
> Let me ping Jens Axboe and find out what he prefers. That should
> give us a good idea of where to continue.

Again, I'd be all for folding, but only when it's actually time to do
so. :}

Daniel

Re: Merging xen/dom0/backend/blktap2 ..

[Konrad Rzeszutek Wilk]

On Sun, Mar 20, 2011 at 06:05:49PM -0700, Daniel Stodden wrote:
> On Sun, 2011-03-20 at 16:28 -0400, Konrad Rzeszutek Wilk wrote:
> 
> > > Proposing a zap_page_range export to mm maintainers will produce a
> > > simple "you're doing it wrong", let's not split commits just for that.
> > > 
> > > My apologies, that detail dates back to the dawn of xen-blktap1.
> > > Userspace is used to mapping a single large VMA, and the driver flips
> > > ptes implicitly as I/O reqs leave and return again. That's machine-wise
> > > not much of a difference, but for normal memory there's mmap/munmap
> > > already, so module code is usually not encouraged to invent funny new VM
> > > area models. Hence, zap_page_range remains private.
> > > 
> > > Can it just resort to mmap/munmap? Probably, even implicitly from ioctl
> > > context I guess.
> > 
> > The gntdev solved this by clearing the PTE on unmap (using the gnttab API and
> > the M2P/P2M override which clears the PTE).
> > 
> > Would that work?
> 
> Well, gntdev gets a normal munmap() from userland when it's time to tear
> down the VMA. That always works, it's how it's meant to be. It's more of
> a challenge for funny PTE types like foreign memory, but I guess that's
> solved now. The latter is not even the case here.

Would it make more sense to have blktap in QEMU? I mean gntdev takes care
of this, and it looks as if most of the manipulation is already done in userspace?

> 
> > > If it hopelessly got in your way, one could back it out, the loss is
> > > TAP=m.
> > > 
> > > > > 
> > > > > > > 
> > > > > > > Does this sound acceptable?
> > > > > > 
> > > > > > I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
> > > > > > merge tree. Can you make a tree that is based off 2.6.38 (or some
> > > > > > branch of my 'stable/' ones). Basically trying to have something that is
> > > > > > easy to merge and is self-containted within one branch.
> > > > > 
> > > > > It is rooted on 2.6.32 and incrementally moves on up to currently
> > > > > v2.6.38, no stray diffs except the forward porting where needed. There's
> > > > > at least one conflict resolution in Kconfig around 36 or 37, iirc. Any
> > > > > later kernel will look more or less the same.
> > > > > 
> > > > > $ git list xenbits/blktap/next-2.6.38 ^v2.6.38
> > > > > eb8040c Merge commit 'v2.6.38' into blktap/next-2.6.38
> > > > > bf926e6 blktap: Forward port to 2.6.37
> > > > > 9f65e90 Merge commit 'v2.6.37' into blktap/next-2.6.37
> > > > > 7ef4e35 blktap: Forward port to 2.6.36
> > > > > a55f064 Merge commit 'v2.6.36' into blktap/next-2.6.36
> > > > > 994a546 blktap: Add discard queue limits.
> > > > > ea2d7e7 Merge blktap into blktap/next-2.6.33
> > > > > e37d737 blktap: Add BLKTAP_OP_TRIM command option.
> > > > > 42276df blktap: Add BLKTAP_OP_FLUSH command option.
> > > > > 5d10876 blktap: Add physical sector device info.
> > > > > 8169b25 blktap: Drop the ring message timestamp.
> > > > > 34574a8 blktap: Support non-R/W requests
> > > > > a765257 blktap: Fix reference to freed struct request.
> > > > > 7ccd87f blktap: Blktap userspace devices.
> > > > > 
> > > > > You could rebase it on v2.6.38 if you want to reproduce the merging and
> > > > > mangle commits, although I'm not sure why. For the foreseeable future,
> > > > > I'd like to keep 2.6.32 and anything later going, so that repo will get
> > > > > incoming stuff at 2.6.32 and, where possible, I'd expect the greater
> > > > 
> > > > Ah, ambitious. I tried that with xen-pcifront and had to resort
> > > > to making trees for different versions. But this could work for you.
> > > 
> > > But it should work fine here. There's only a single source tree, which
> > > is linux-2.6.git, and only a single component, which aims to yield the
> > > same extensions where possible. Doesn't get much easier than that.
> > > 
> > > I'd agree that components interfacing with 4 moving xen subsystems, as
> > > in blkback etc. is a bit of a different matter.
> > > 
> > > Still, killing history altogether can't be the answer.
> > 
> > Seems to be the answer nowadays. David Miller asked Ian to squash the full
> > history in one commit, and provide a "historic" git tree where all of the
> > git commits reside.
> 
> For an upstream intro, sure. I'd probably ask for the same if I were the
> maintainer. No surprise.
> 
> >From there on, even merging branches is probably fine again, provided
> individual commits don't relate and there's no fix-this/forgot-that
> stuff documenting how people got there. Nobody needs that in mainline.
> 
> > > 
> > > > > kernels to typically just fast-forward from where they are now.
> > > > 
> > > > The issue is git bisection. The dates on those commits is quite early so
> > > > I wonder if somebody did a git bisect whether they would hit those and
> > > > end up with compilation issues. Perhaps the first patch should
> > > > just introduce the driver, but not touch the Kconfig at all.
> > > > 
> > > > And then the last one actually enables the Kconfig. And as you
> > > > add updates, you move the patch with Kconfig to be the last one?
> > > > 
> > > > > 
> > > > > If you want topic branches: I'm not planning to do those. Mainly because
> > > > > it's a bad idea. If that entire thing would be about to go upstream with
> > > > > limited time to land that might a different thing, but it's clearly not
> > > > > there in its present state.
> > > > 
> > > > What is a "bad" about it? What do you want to do when the driver is ready
> > > > for upstream? You would have to do this topic branch at some point, wouldn't you?
> > > > What is a topic branch to you? When I think topic branch I think:
> > > > devel/xen-pciback-0.5 for example.
> > > 
> > > When (iff) that driver gets ready for upstream I guess it'd have to be
> > > folded down and optionally split, pretty much exactly as you describe.
> > > 
> > > This is my third attempt to write a proper response to your concerns,
> > > because so far I'm not super-experienced with git either.
> > > 
> > > I was going to disagree because keeping separate queues is a bit of a
> > > workflow killer.
> > > 
> > > Then I was going to agree because commit atomicity for proper bisection
> > > is a actually pretty good point, imho.
> > > 
> > > The thing I hate about rebasing/cherry-picking is not even the extra
> > > work, it's that the dupes mean one loses any kind of traction wrt what's
> > > in a particular derived tree and not. So in order to be able to compare
> > > two such branches one has to diff sources, git-blame, and understanding
> > > a whole lot too much about the content.
> > 
> > Or:
> > git shortlog devel/xen-pciback-0.3..devel/xen-pciback-0.5  --grep="pciback"
> > 
> > Which gives you some good idea of what was added... that is if one
> > does not mess with the git commits and amend them (which I sometimes too
> > since they are still "devel").
> 
> I'm assuming pciback-0.5 supersedes/deprecates pciback-0.3?

Yes.
> 
> > > The commit atomicity issue could be solved by making sure stay in a
> > > branch, and only get merged, not pulled through by fast-forward. That
> > > git-merge --no-ff option looks like it was meant to ensure that.
> > > 
> > > There's another way to make stuff atomic: Amending merges with the
> > > following port. A git-commit --amend can do that. Took me ages to find
> > > that out, because for reasons unclear, git-rebase -i alone (as 'fixup'
> > > changes) can't.
> > > 
> > > I tried whether that's better. Can't recommend it. Git appears to have a
> > > really hard time turning such ports/merges back into diffs, and having
> > > those diffs is quite useful. It's not impossible, but format-patch alone
> > > can't, which gets a bit counterintuitive.
> > > 
> > > > The reason I am asking about this is b/c of my inept git skills. Doing
> > > > "git pull daniel/blktap" and just having it fetch patches that are relevant
> > > > to blktap makes it soooo much easier to get an idea what is happening.
> > > 
> > > Well, it's not like it's going to pull garbage. These are all blktap
> > > exclusively, rooted at v2.6.38. Just not ported individually, but in
> > > piles.
> > 
> > OK. The desciption were a bit generic: "porting to 2.6.37" .. doesn't really
> > tell what you had to do, or what not. I did not look in the description, so
> > it might have had the details.
> 
> There are more details in the commit message. But as far as I can tell,
> there's not much point in splitting them any more thoroughly.
> 
> > > Let's assume one would go through the pain to port those one after one,
> > > by cherry-picking and careful rebuild. With 2.6.39 one had to start over
> > > again, porting every commit once again, and making sure it compiles to
> > > stay consistent, again for bisection purposes. And so on, every couple
> > > months at least.
> > 
> > That can be automated quite easily. The .git/hooks can do the make process
> > automatic before checking it, and failing if it is not working.
> >
> > So once you set that up, it is as simple as 'git rebase -i v2.6.39'...
> > but I am not sure if that is needed.
> > 
> > The reason you might need to rebase it is if the newer tree has thrown some
> > API out or introduced a new one that the blktap can use. But if that is
> > not the case, there should be no trouble on a 2.6.40 tree to do:
> 
> I'd probably make that another patch on top.
> 
> > git merge <devel-tree-based-on-2.6.36> .. and fix up the little merge
> > issues (if any).
> > 
> > > 
> > > That continues, until this thing gets either dropped or upstreamed, at
> > > which time an O(n*m) disaster gets folded down and discarded, one way or
> > > the other. That not very efficient.
> > 
> > The whole upstream effort is not efficient at all :-) It sometimes
> > is akin to trying to convience a tax auditor that they are wrong.
> 
> Well yeah. But my concern here, again, is not upstreaming. The problem
> is that 2.6.38 is important, but not integral. There's 2.6.32, XCP,
> XenClient and all those trees will remain under maintenance. A merge and
> forward port is more efficient than rebasing.

Aah, ok. So more of keeping sanity with all of those products and having the
same type of patches in all of those trees.

> 
> > > The reality is it looks like git can't deal with it any better that what
> > > I got there.
> > > 
> > > So I'd rather ask you open a konrad/blktap-2.6.38, tracking that branch,
> > > and carefully merge that in, in a way not risking bisection.
> > 
> > OK. Bisection is important - especially during those rc-X cycles where
> > stuff stops working and is a tangle to figure out what went wrong.
> > 
> > And it sounds to me that you want to defeer the idea of upstreaming
> > for some time, and when you are comfortable with blktap2 being in great
> > shape - then start the process.
> 
> There's more work, and it's far beyond mmap. I'd first have to talk to
> people about some of the implications which I can't just fix in there.
> 
> The whole blkdev-in-userspace thing looks like an obviously good idea.
> Like FUSE. It's been envisioned as just that. But while it works fine
> under guests, upstreaming would implicitly promote it to carry host I/O.

What do you mean by 'host' here? The guest or dom0?

> Now, in that area, XCP carries a couple extra patches to help dom0 with
> provisioning of disk images under memory congestion. You really don't
> want to know about those.

Sounds quite enterprise worthy type of feature.
> 
> > When it comes to upstreaming process the fashion looks to post one
> > nice patch that includes the driver. Infrastructure patches should be
> > done as seperate patches. So at that point it probably won't matter
> > at all whether you have little bits of patches, or just one big one.
> > The maintainer (Jens Axboe) will probably just pick the big one.
> > 
> > > 
> > > If that's okay, next question would probably be if one shouldn't try do
> > > the same with blkback >:)
> > 
> > For authorship I prefer to keep branches. So say I post the blbkback
> > driver "as is" for review. People come back with reviews, or what not - I create
> > a new branch with a new patch with the review feedback. That way when
> > I am finally done, I've this "historic" branch that has all the names of
> > people who contributed to it.
> > 
> > There is a twist to all of this. Linus himself prefers to ingest whole
> > git branches. Other maintainers, like just one single patch.
> > 
> > Let me ping Jens Axboe and find out what he prefers. That should
> > give us a good idea of where to continue.
> 
> Again, I'd be all for folding, but only when it's actually time to do
> so. :}

Right. I think that is something we will have to address later on. As I understand
you are looking at this from "how to keep all my patches synced across all those
branches".

And then later on jump to implement blktap in QEMU. But my worry is that it wont
happen. Not because of lazines - but rather priority shift. There are going to be bugs,
request for new features, testing, stabilizing. This will all take time that will
be taken away from upstreaming "blktap-ish".

Maybe we should just drop the idea of upstreaming this? At which point I shouldn't
carry it in my devel branch (which is for patches we want to upstream) but instead
create a branch that would be used for those folks who want all patches that
went upstream + some goodies that aren't going to be upstreamed?

Re: Merging xen/dom0/backend/blktap2 ..

[Daniel Stodden]

On Tue, 2011-03-22 at 12:59 -0400, Konrad Rzeszutek Wilk wrote:

> > >
> > > The gntdev solved this by clearing the PTE on unmap (using the gnttab API and
> > > the M2P/P2M override which clears the PTE).
> > >
> > > Would that work?
> >
> > Well, gntdev gets a normal munmap() from userland when it's time to tear
> > down the VMA. That always works, it's how it's meant to be. It's more of
> > a challenge for funny PTE types like foreign memory, but I guess that's
> > solved now. The latter is not even the case here.
> 
> Would it make more sense to have blktap in QEMU? I mean gntdev takes care
> of this, and it looks as if most of the manipulation is already done in userspace?

Not at this point, and not in the foreseeable future. But it would make
sense to have blktap running guest I/O against gntdev, yes.

I used to have a prototype for the datapath, but there were quite some
gntdev changes and those must have bitrotted quite terribly since the
beginning of the year. I hope to get to look into it again in Q2.

> > > > If it hopelessly got in your way, one could back it out, the loss is
> > > > TAP=m.
> > > >
> > > > > >
> > > > > > > >
> > > > > > > > Does this sound acceptable?
> > > > > > >
> > > > > > > I looked briefly at blktap/next-2.6.38 and it looks like an ongoing
> > > > > > > merge tree. Can you make a tree that is based off 2.6.38 (or some
> > > > > > > branch of my 'stable/' ones). Basically trying to have something that is
> > > > > > > easy to merge and is self-containted within one branch.
> > > > > >
> > > > > > It is rooted on 2.6.32 and incrementally moves on up to currently
> > > > > > v2.6.38, no stray diffs except the forward porting where needed. There's
> > > > > > at least one conflict resolution in Kconfig around 36 or 37, iirc. Any
> > > > > > later kernel will look more or less the same.
> > > > > >
> > > > > > $ git list xenbits/blktap/next-2.6.38 ^v2.6.38
> > > > > > eb8040c Merge commit 'v2.6.38' into blktap/next-2.6.38
> > > > > > bf926e6 blktap: Forward port to 2.6.37
> > > > > > 9f65e90 Merge commit 'v2.6.37' into blktap/next-2.6.37
> > > > > > 7ef4e35 blktap: Forward port to 2.6.36
> > > > > > a55f064 Merge commit 'v2.6.36' into blktap/next-2.6.36
> > > > > > 994a546 blktap: Add discard queue limits.
> > > > > > ea2d7e7 Merge blktap into blktap/next-2.6.33
> > > > > > e37d737 blktap: Add BLKTAP_OP_TRIM command option.
> > > > > > 42276df blktap: Add BLKTAP_OP_FLUSH command option.
> > > > > > 5d10876 blktap: Add physical sector device info.
> > > > > > 8169b25 blktap: Drop the ring message timestamp.
> > > > > > 34574a8 blktap: Support non-R/W requests
> > > > > > a765257 blktap: Fix reference to freed struct request.
> > > > > > 7ccd87f blktap: Blktap userspace devices.
> > > > > >
> > > > > > You could rebase it on v2.6.38 if you want to reproduce the merging and
> > > > > > mangle commits, although I'm not sure why. For the foreseeable future,
> > > > > > I'd like to keep 2.6.32 and anything later going, so that repo will get
> > > > > > incoming stuff at 2.6.32 and, where possible, I'd expect the greater
> > > > >
> > > > > Ah, ambitious. I tried that with xen-pcifront and had to resort
> > > > > to making trees for different versions. But this could work for you.
> > > >
> > > > But it should work fine here. There's only a single source tree, which
> > > > is linux-2.6.git, and only a single component, which aims to yield the
> > > > same extensions where possible. Doesn't get much easier than that.
> > > >
> > > > I'd agree that components interfacing with 4 moving xen subsystems, as
> > > > in blkback etc. is a bit of a different matter.
> > > >
> > > > Still, killing history altogether can't be the answer.
> > >
> > > Seems to be the answer nowadays. David Miller asked Ian to squash the full
> > > history in one commit, and provide a "historic" git tree where all of the
> > > git commits reside.
> >
> > For an upstream intro, sure. I'd probably ask for the same if I were the
> > maintainer. No surprise.
> >
> > >From there on, even merging branches is probably fine again, provided
> > individual commits don't relate and there's no fix-this/forgot-that
> > stuff documenting how people got there. Nobody needs that in mainline.
> >
> > > >
> > > > > > kernels to typically just fast-forward from where they are now.
> > > > >
> > > > > The issue is git bisection. The dates on those commits is quite early so
> > > > > I wonder if somebody did a git bisect whether they would hit those and
> > > > > end up with compilation issues. Perhaps the first patch should
> > > > > just introduce the driver, but not touch the Kconfig at all.
> > > > >
> > > > > And then the last one actually enables the Kconfig. And as you
> > > > > add updates, you move the patch with Kconfig to be the last one?
> > > > >
> > > > > >
> > > > > > If you want topic branches: I'm not planning to do those. Mainly because
> > > > > > it's a bad idea. If that entire thing would be about to go upstream with
> > > > > > limited time to land that might a different thing, but it's clearly not
> > > > > > there in its present state.
> > > > >
> > > > > What is a "bad" about it? What do you want to do when the driver is ready
> > > > > for upstream? You would have to do this topic branch at some point, wouldn't you?
> > > > > What is a topic branch to you? When I think topic branch I think:
> > > > > devel/xen-pciback-0.5 for example.
> > > >
> > > > When (iff) that driver gets ready for upstream I guess it'd have to be
> > > > folded down and optionally split, pretty much exactly as you describe.
> > > >
> > > > This is my third attempt to write a proper response to your concerns,
> > > > because so far I'm not super-experienced with git either.
> > > >
> > > > I was going to disagree because keeping separate queues is a bit of a
> > > > workflow killer.
> > > >
> > > > Then I was going to agree because commit atomicity for proper bisection
> > > > is a actually pretty good point, imho.
> > > >
> > > > The thing I hate about rebasing/cherry-picking is not even the extra
> > > > work, it's that the dupes mean one loses any kind of traction wrt what's
> > > > in a particular derived tree and not. So in order to be able to compare
> > > > two such branches one has to diff sources, git-blame, and understanding
> > > > a whole lot too much about the content.
> > >
> > > Or:
> > > git shortlog devel/xen-pciback-0.3..devel/xen-pciback-0.5  --grep="pciback"
> > >
> > > Which gives you some good idea of what was added... that is if one
> > > does not mess with the git commits and amend them (which I sometimes too
> > > since they are still "devel").
> >
> > I'm assuming pciback-0.5 supersedes/deprecates pciback-0.3?
> 
> Yes.

Well, that probably works okay, but it's not the kind of thing I'm
after. I'm trying to maintain a couple branches crossing kernel
releases. Merging is flawed, but it's all in git which tracks commits
across branches.

> > > > The commit atomicity issue could be solved by making sure stay in a
> > > > branch, and only get merged, not pulled through by fast-forward. That
> > > > git-merge --no-ff option looks like it was meant to ensure that.
> > > >
> > > > There's another way to make stuff atomic: Amending merges with the
> > > > following port. A git-commit --amend can do that. Took me ages to find
> > > > that out, because for reasons unclear, git-rebase -i alone (as 'fixup'
> > > > changes) can't.
> > > >
> > > > I tried whether that's better. Can't recommend it. Git appears to have a
> > > > really hard time turning such ports/merges back into diffs, and having
> > > > those diffs is quite useful. It's not impossible, but format-patch alone
> > > > can't, which gets a bit counterintuitive.
> > > >
> > > > > The reason I am asking about this is b/c of my inept git skills. Doing
> > > > > "git pull daniel/blktap" and just having it fetch patches that are relevant
> > > > > to blktap makes it soooo much easier to get an idea what is happening.
> > > >
> > > > Well, it's not like it's going to pull garbage. These are all blktap
> > > > exclusively, rooted at v2.6.38. Just not ported individually, but in
> > > > piles.
> > >
> > > OK. The desciption were a bit generic: "porting to 2.6.37" .. doesn't really
> > > tell what you had to do, or what not. I did not look in the description, so
> > > it might have had the details.

> > Well yeah. But my concern here, again, is not upstreaming. The problem
> > is that 2.6.38 is important, but not integral. There's 2.6.32, XCP,
> > XenClient and all those trees will remain under maintenance. A merge and
> > forward port is more efficient than rebasing.
> 
> Aah, ok. So more of keeping sanity with all of those products and having the
> same type of patches in all of those trees.

Exactly. So the idea was to feed all patches into next-2.6.32 and from
there carry them on to 2.6.38. Later branches start as soon as there are
block layer changes which justify starting a new one.

If konrad/2.6.38 commits patches before I got to pick them up, I'd still
cherry-pick them back, as far as applicable, and push them up to
next-2.6.38 again. That's causing dupes on your side, but they should
merge fine. The opportunity should be rare.

The only reasonable alternative to pulling in merged branches, if merged
trees definitely don't work for you, is a for-konrad tree folding down
every merge into a single update. That's really simple to do, so if
that's preferred the question would be whether you want me to prepare
those.

Porting piles of patches individually isn't efficient nor justified.
Most people will just want a stable tree to pull from with all updates,
fix more issues, mail diffs, and move on. And upstreaming modules would
fold down even more aggressively, so the effort of porting individually
is quite moot.

> >
> > > > The reality is it looks like git can't deal with it any better that what
> > > > I got there.
> > > >
> > > > So I'd rather ask you open a konrad/blktap-2.6.38, tracking that branch,
> > > > and carefully merge that in, in a way not risking bisection.
> > >
> > > OK. Bisection is important - especially during those rc-X cycles where
> > > stuff stops working and is a tangle to figure out what went wrong.
> > >
> > > And it sounds to me that you want to defeer the idea of upstreaming
> > > for some time, and when you are comfortable with blktap2 being in great
> > > shape - then start the process.
> >
> > There's more work, and it's far beyond mmap. I'd first have to talk to
> > people about some of the implications which I can't just fix in there.
> >
> > The whole blkdev-in-userspace thing looks like an obviously good idea.
> > Like FUSE. It's been envisioned as just that. But while it works fine
> > under guests, upstreaming would implicitly promote it to carry host I/O.
> 
> What do you mean by 'host' here? The guest or dom0?

Any kernel running blktap, and wishing to run I/O not on behalf of
guests but it's own applications. That's the general use case for what
blktap suggests it does. But there dependency cycles which must be
avoided, or broken.

> > Now, in that area, XCP carries a couple extra patches to help dom0 with
> > provisioning of disk images under memory congestion. You really don't
> > want to know about those.
> 
> Sounds quite enterprise worthy type of feature.

Well, it typically depends on how you e.g. bootstrap VMs. Firing up the
VM and launching the installer is always fine. Getting yourself under
serious memory pressure, then having an RPC coming in which takes a
master image and blows it through the dom0 pagecache into a VHD is
different.

> > > When it comes to upstreaming process the fashion looks to post one
> > > nice patch that includes the driver. Infrastructure patches should be
> > > done as seperate patches. So at that point it probably won't matter
> > > at all whether you have little bits of patches, or just one big one.
> > > The maintainer (Jens Axboe) will probably just pick the big one.
> > >
> > > >
> > > > If that's okay, next question would probably be if one shouldn't try do
> > > > the same with blkback >:)
> > >
> > > For authorship I prefer to keep branches. So say I post the blbkback
> > > driver "as is" for review. People come back with reviews, or what not - I create
> > > a new branch with a new patch with the review feedback. That way when
> > > I am finally done, I've this "historic" branch that has all the names of
> > > people who contributed to it.
> > >
> > > There is a twist to all of this. Linus himself prefers to ingest whole
> > > git branches. Other maintainers, like just one single patch.
> > >
> > > Let me ping Jens Axboe and find out what he prefers. That should
> > > give us a good idea of where to continue.
> >
> > Again, I'd be all for folding, but only when it's actually time to do
> > so. :}
> 
> Right. I think that is something we will have to address later on. As I understand
> you are looking at this from "how to keep all my patches synced across all those
> branches".
> 
> And then later on jump to implement blktap in QEMU. But my worry is that it wont
> happen. Not because of lazines - but rather priority shift. There are going to be bugs,
> request for new features, testing, stabilizing. This will all take time that will
> be taken away from upstreaming "blktap-ish".
> 
> Maybe we should just drop the idea of upstreaming this? At which point I shouldn't
> carry it in my devel branch (which is for patches we want to upstream) but instead
> create a branch that would be used for those folks who want all patches that
> went upstream + some goodies that aren't going to be upstreamed?

We can drop the idea for a while, yes. I'm not sure if that justifies
just dropping it out of the tree. That's ultimately up to your
judgement, but the code footprint across the component branches is
already next to zero. Blktap isn't in xen/ or core stuff anymore. Export
zap_page_range being the single exception, but that residual isn't very
prone to crosstalk.

Thanks,
Daniel