[libvirt] [PATCH v2 06/12] qemu: Generate cmd line at startup

[Peter Krempa]

On Fri, Mar 02, 2018 at 08:22:32 -0500, John Ferlan wrote:
> 
> 
> On 02/21/2018 01:11 PM, Michal Privoznik wrote:
> > This is the easier part. All we need to do here is put -object
> > pr-manger-helper,id=$alias,path=$socketPath and then just
> > reference the object in -drive file.pr-manger=$alias.
> 
> s/manger/manager/
> 
> My fingers usually the same way though as manger
> 
> > 
> > Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> > ---
> >  src/qemu/qemu_command.c                            | 40 ++++++++++++++++++++++
> >  .../disk-virtio-scsi-reservations-not-managed.args | 28 +++++++++++++++
> >  .../disk-virtio-scsi-reservations.args             | 29 ++++++++++++++++
> >  tests/qemuxml2argvtest.c                           |  8 +++++
> >  4 files changed, 105 insertions(+)
> >  create mode 100644 tests/qemuxml2argvdata/disk-virtio-scsi-reservations-not-managed.args
> >  create mode 100644 tests/qemuxml2argvdata/disk-virtio-scsi-reservations.args
> > 
> > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> > index fa0aa5d5c..069d60d35 100644
> > --- a/src/qemu/qemu_command.c
> > +++ b/src/qemu/qemu_command.c
> > @@ -1514,6 +1514,20 @@ qemuDiskSourceGetProps(virStorageSourcePtr src)
> >  }
> >  
> >  
> > +static void
> > +qemuBuildDriveSourcePR(virBufferPtr buf,
> > +                       virStorageSourcePtr src)
> > +{
> > +    qemuDomainStorageSourcePrivatePtr srcPriv = QEMU_DOMAIN_STORAGE_SOURCE_PRIVATE(src);
> > +    qemuDomainDiskPRDPtr prd = srcPriv->prd;
> > +
> > +    if (!prd || !prd->alias)
> > +        return;
> > +
> > +    virBufferAsprintf(buf, ",file.pr-manager=%s", prd->alias);
> > +}
> > +
> > +
> >  static int
> >  qemuBuildDriveSourceStr(virDomainDiskDefPtr disk,
> >                          virQEMUCapsPtr qemuCaps,
> > @@ -1590,6 +1604,8 @@ qemuBuildDriveSourceStr(virDomainDiskDefPtr disk,
> >  
> >          if (disk->src->debug)
> >              virBufferAsprintf(buf, ",file.debug=%d", disk->src->debugLevel);
> > +
> > +        qemuBuildDriveSourcePR(buf, disk->src);
> >      } else {
> >          if (!(source = virQEMUBuildDriveCommandlineFromJSON(srcprops)))
> >              goto cleanup;
> > @@ -9789,6 +9805,28 @@ qemuBuildPanicCommandLine(virCommandPtr cmd,
> >  }
> >  
> >  
> > +static void
> > +qemuBuildMasterPRCommandLine(virCommandPtr cmd,
> > +                             const virDomainDef *def)
> > +{
> > +    size_t i;
> > +
> > +    for (i = 0; i < def->ndisks; i++) {
> > +        const virDomainDiskDef *disk = def->disks[i];
> > +        qemuDomainStorageSourcePrivatePtr srcPriv = QEMU_DOMAIN_STORAGE_SOURCE_PRIVATE(disk->src);
> > +        qemuDomainDiskPRDPtr prd = srcPriv->prd;
> > +        virBuffer buf = VIR_BUFFER_INITIALIZER;
> > +
> > +        if (!prd || !prd->alias)
> > +            continue;
> > +
> > +        virBufferAsprintf(&buf, "pr-manager-helper,id=%s,path=%s", prd->alias, prd->path);
> > +        virCommandAddArg(cmd, "-object");
> > +        virCommandAddArgBuffer(cmd, &buf);
> 
> What happens when there's more than one disk using the managed mode
> where you have a "static" alias and path, wouldn't there be multiple
> lines with:
> 
> -object
> pr-manager-helper,id=pr-helper0,path=/tmp/lib/domain--1-QEMUGuest1/pr-helper0.sock
> 
> ?  And how is QEMU going to react to that?
> 
> IOW: Shouldn't this code know it's already created an object for that
> case and not generate another one?
> 
> The other one :
> 
> -object pr-manager-helper,id=pr-helper-sdb,path=/path/to/qemu-pr-helper.sock
> 
> I get, but I'm still not thrilled with "sdb" as opposed to the
> disk->info.alias of "scsi0-0-0-0" more commonly used. IIRC, there's no
> guarantee that what libvirt calls "sdb" ends up being "sdb" on the
> guest. My vague recollection of the algorithm that "automagically"
> generates the address based on sda, sdb, sdc, etc. So "sdb" IIRC would
> related to an address that would create an alias using "0-0-1"; whereas,
> "sda" would create that "0-0-0" value.
> 
> The fact that you've defined the <address> and <target> originally
> avoids the virDomainDiskDefAssignAddress algorithm. Also see the
> virDiskNameToBusDeviceIndex as well as the virDomainHostdevAssignAddress
> (and code around that) in order to see the awfulness of which I write.
> The real fun begins when you have <disk>'s and <hostdev>'s.
> 
> BTW: Seeing this and thinking about the command line jiggles a memory
> thread related to virStorageSourceParseBacking* and related tests where
> the code can handle various JSON outputs where it's not clear to me
> whether you'll need to add tests for the "file.pr-manager" processing. I
> think you might, but Peter understands more of that than I do.

No, this should not be handled in JSON at all. Referencing an alias in
JSON is wrong since it is tied to the one single run of the VM where
that would be created and could be something completely different in any
other run of the VM
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