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Re: [libvirt] doc: write separate module for hostdev passthrough and in-use tracking



On 25/03/13 14:51, Chunyan Liu wrote:
2013/3/22 Osier Yang <jyang redhat com>:
On 2013年03月22日 17:36, Chunyan Liu wrote:
Hi, List,

As the mail I've sent a week before:
https://www.redhat.com/archives/libvir-list/2013-March/msg00730.html
I'm willing to push this work forward so that the passthrough APIs
could be reused by qemu driver and libxl driver (which doesn't support
pci passthrough yet and tries to add this function recently), or other
drivers.

But since this work affacts a lot, I'm not sure if I can control it in
a correct way. I write a draft to describe what I'm considering how to
do, as in the following and in attachment. Hope to get your review,
comment and guidence to improve the work before start coding. Any
feedback will be very appreciated!

Thanks!
Chunyan

------------------------
DRAFT:

Write separate module for hostdev passthrough

Cool. we lacked this for a time.


1. Purposes:

     * Move hostdev passthrough APIs from qemu_hostdev.ch to separate
module so
       that they could be reused by other hypervisors too

     * Maintain global in-use state of hostdevs

This is more important than the code-reuse.



2. Module design (draft):

     * New module name: hostdev_driver

     * New module files: hostdev_driver.ch hostdev_conf.ch

     * New Definitions:

          ## [src/driver.h]

          typedef struct _virHostdevDriver virHostdevDriver;

          typedef virHostdevDriver *virHostdevDriverPtr;

          struct _virHosedevDriver {
              const char *name;
              virDrvOpen                  open;
              virDrvClose                 close;

              virDrvPrepareHostdevs        prepareHostdevs;
              virDrvPreparePciHostdevs        preparePciHostdevs;
              virDrvprepareUsbHostdevs        prepareUsbHostdevs;

In case of you want to expose prepareHostdevs, no need to expose
preparePciHostdevs and prepareUsbHostdevs?
Thanks very much for your comments.

Exposing these two APIs is considering that some driver may supports
one but not another, so that it could call specific API. But we can
use support flag in prepareHostdevs to control that, in this way not
need these two APIs

              virDrvReattachHostdevs        reattachHostdevs;
              virDrvReattachPciHostdevs        reattachPciHostdevs;
              virDrvReattachUsbHostdevs       reattachUsbHostdevs;

Likewise.


              virDrvGetActivePciHostdevList       getActivePciHostdevList;
              virDrvGetActiveUsbHostdevList       getActiveUsbHostdevList;
              virDrvGetDomainActivePciHostdevList
getDomainActivePciHostdevList;
              virDrvGetDomainActiveUsbHostdevList
getDomainActiveUsbHostdevList;

These APIs are useful for upper layer management too. I have once
wanted to create similiar APIs, but only tended for qemu driver
at that time.

But except these 4 get APIs, others are only useful for other drivers
(internally), useless for upper layer management.
That's true.

Do we really want a
driver instead of just an internal share module? Like src/nodeinfo.[ch],
and with it we still can expose APIs like the 4 get APIs.
Do you mean add src/hostdev.[ch] and do all work there? Think a while,
I think it can achieve too.

Yes.

Then do we need to differentiate 4 get
APIs and other APIs?

Not sure about you meaning here. But you can take the existing APIs like
virNodeSetMemoryParameters as examples.  The API is implemented
in src/nodeinfo.[ch], but each driver can use it.



             };

          ## [src/hostdev/hostdev_conf.h]

          typedef struct _virHostdevDriverState virHostdevDriverState;

          typedef virHostdevDriverState *virHostdevDriverStatePtr;

          struct _virHostdevDriverState {
              virMutex lock;
              virPCIDeviceListPtr activePciHostdevs;
              virPCIDeviceListPtr inactivePciHostdevs;
              virUSBDeviceListPtr activeUsbHostdevs;
          };

          ## [src/hostdev/hostdev_driver.c]

          static virHostdevDriver hostdevDriver = {
              .name = "hostdev",
              .open = hostdevDriverOpen,
              .close = hostdevDriverClose,
              .prepareHostdevs = virPrepareHostdevs,
              .preparePciHostdevs = virPreparePciHostdevs,
              .prepareUsbHostdevs = virPrepareUsbHostdevs
              .reattachHostdevs = virReattachHostdevs,
              .reattachPciHostdevs = virReattachPciHostdevs,
              .reattachUsbHostdevs = virReattachUsbHostdevs,
              .getActivePciHostdevList = virGetActivePciHostdevList,
              .getActiveUsbHostdevList = virGetActiveUsbHostdevList,
              .getDomainActivePciHostdevList =
virGetDomainActivePciHostdevList,
              .getDomainActiveUsbHostdevList =
virGetDomainActiveUsbHostdevList,
          };

          static virStateDriver hostdevStateDriver = {
              .name = "hostdev",
              .initialize = hostdevDriverStartup,
              .cleanup = hostdevDriverCleanup,
              .reload = hostdevDriverReload,
          };

     * Changed Definitions:

          struct _virPCIDevice {
              ......

              --- const char    *used_by;  /* The domain which uses the
device */
              +++ virDomainObjPtr used_by;  /* include domname and conn
info */

Why need the "conn info"? Isn't a driver name enough here?
Driver name is OK. Just need to fill unique info about the device is
used by which driver which domain. So I try to store virDomainObjPtr
to the used_by area, from this pointer, we can get driver name and
domain name. Do you think that's OK?

Yeah, I think virDomainObjPtr is just overkill, you have to maintain
the object's lifecycle.



              ......
          };

          struct _virUSBDevice {
              ......
              --- const char    *used_by;  /* name of the domain using this
dev */
              +++ virDomainObjPtr used_by;  /* include domname and conn
info */
          };

     * APIs:

          typedef int
          (*virDrvPrepareHostdevs)(virHostdevDriverPtr driver,
                                   virDomainObjPtr vm,
                                   unsigned int flags);
             /*
             - workflow:
               call PrepareHostdevPciDevices and PrepareHostdevUsbDevices
               to do specific work.

             - reference:
               int qemuPrepareHostDevices(virQEMUDriverPtr driver,
                             virDomainDefPtr def,
                             bool coldBoot);

             - new parameter:
               - flags:
                 - could set "coldBoot" for usb usage
                 - could set hypervisor tag since for qemu it will use
                   pci-stub, for libxl, it will use pciback.
             */

          typedef int
          (*virDrvPreparePciHostdevs)(virHostdevDriverPtr driver,
                                   virDomainObjPtr vm,
                                   virDomainHostdevDefPtr *hostdevs,
                                   int nhostdevs,
                                   unsigned int flags);
             /*
             - workflow:
               1. check things (e.g. assignability to non-managed device)
               2. detach managed device and reset work
               3. set usedby to 'vm', update activePciHostdevs and
                  inactivePciHostdevs

             - reference:
               int qemuPrepareHostdevPCIDevices(virQEMUDriverPtr driver,
                                   const char *name,
                                   const unsigned char *uuid,
                                   virDomainHostdevDefPtr *hostdevs,
                                   int nhostdevs);
              */

          typedef int
          (*virDrvprepareUsbHostdevs)((virHostdevDriverPtr driver,
                                   virDomainObjPtr vm,
                                   virUSBDeviceListPtr list);
             /*
             - workflow:
               check usb device, set usedby to 'vm', update
activeUsbHostdevs

             - reference:
               int qemuPrepareHostdevUSBDevices(virQEMUDriverPtr driver,
                                   const char *name,
                                   virUSBDeviceListPtr list);
             */

          typedef void
          (*virDrvReattachHostdevs)(virHostdevDriverPtr driver,
                                     virDomainObjPtr vm);
             /*
             - workflow:
                call reattachPciHostDevices and reattachUsbHostDevices to
                do specific work.

             - reference:
                void qemuDomainReAttachHostDevices(virQEMUDriverPtr driver,
                                     virDomainDefPtr def)
             */

          typedef void
          (*virDrvReattachPciHostdevs) (virHostdevDriverPtr driver,
                                        virDomainObjPtr vm,
                                        virDomainHostdevDefPtr *hostdevs,
                                        int nhostdevs);
             /*
             - workflow:
                unbind and bind to original driver, free
                usedby, activePciHostdevs and inactivePciHostdevs.

             - reference:
                void
qemuDomainReAttachHostdevDevices(virQEMUDriverPtrdriver,
                                        const char *name,
                                        virDomainHostdevDefPtr *hostdevs,
                                        int nhostdevs)
             */

          typedef void
          (*virDrvReattachUsbHostdevs) (virHostdevDriverPtr driver,
                                   virDomainObjPtr vm,
                                   virDomainHostdevDefPtr *hostdevs,
                                   int nhostdevs);
             /*
             - workflow:
                free usedby, activePciHostdevs and inactivePciHostdevs.

             - reference:
                static void
                qemuDomainReAttachHostUsbDevices(virQEMUDriverPtr driver,
                                   const char *name,
                                   virDomainHostdevDefPtr *hostdevs,
                                   int nhostdevs)
             */

          typedef virPCIDeviceListPtr
          (*virDrvGetActivePciHostdevList) (virHostdevDriverPtr driver);
             /*
             - could be used to check if a pci hostdev is already in-use.
             */

          typedef virUSBDeviceListPtr
          (*virDrvGetActiveUsbHostdevList) (virHostdevDriverPtr driver);
             /*
             - could be used to check if a usb hostdev is already in-use.
             */

          typedef virPCIDeviceListPtr
          (*virDrvGetDomainActivePciHostdevList) (virHostdevDriverPtr
driver);
             /*
             - could be used to reattach all in-use pci hostdevs by a
               domain (e.g. when a domain shutdown)
             */

          typedef virUSBDeviceListPtr
          (*virDrvGetDomainActiveUsbHostdevList) (virHostdevDriverPtr
driver);
             /*
             - could be used to reattach all in-use usb hostdevs by a
               domain
             */

So it needs to expose the virPCI{USB}DeviceList to public. Not sure how
useful it will be to expose the struct, instead of the ID of the
devices.
The case I was considering here is: when reattaching hostdevs in vm
shutoff, 'managed' or 'non-managed' info is also needed. But in this
case, it is internally used, we can also handle that in
virDrvReattachHostdevs.
Could "managed=yes/no" info be used somewhere else? If not, then seems
ID is enough.

"managed=yes/no" is only used by attaching/detaching, nodedev-dettach
and nodedev-reattach.


These APIs could be used for node device driver. To filter the active/
inactive devices.


3. Use the module

      * Register hostdev driver
          - define 'virHostdevDriverTab' and 'virHostdevDriverTabCount'
          - add hostdev driver register work in libvirtd.c
daemonInitialize()

      * add hostdev driver areas to _virConnect
          struct _virConnect {
              .......
              virNWFilterDriverPtr nwfilterDriver;
          +++ virHostdevDriverPtr hostdevDriver;

              .......
              void *            nwfilterPrivateData;
          +++ void *            hostdevPrivateData;
              .......
          }


      * add conn->hostdevDriver parser in libvirt.c: do_open()
        Then hypervisor drivers can get use of hostdev driver APIs.

      * moments that could be affacted:
          - domain start/shutoff
          - attach/detach hostdev to domain

And libvirt restarting.

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