[Qemu-devel] Re: [PATCH 1/2] Implement drive_del to decouple block removal from device removal

[Ryan Harper <ryanh@us.ibm.com>]

* Kevin Wolf <kwolf@redhat.com> [2010-11-12 10:43]:
> Am 12.11.2010 16:38, schrieb Ryan Harper:
> > Currently device hotplug removal code is tied to device removal via
> > ACPI.  All pci devices that are removable via device_del() require the
> > guest to respond to the request.  In some cases the guest may not
> > respond leaving the device still accessible to the guest.  The management
> > layer doesn't currently have a reliable way to revoke access to host
> > resource in the presence of an uncooperative guest.
> > 
> > This patch implements a new monitor command, drive_del, which
> > provides an explicit command to revoke access to a host block device.
> > 
> > drive_del first quiesces the block device (qemu_aio_flush;
> > bdrv_flush() and bdrv_close()).  This prevents further IO from being
> > submitted against the host device.  Finally, drive_del cleans up
> > pointers between the drive object (host resource) and the device
> > object (guest resource).
> > 
> > Signed-off-by: Ryan Harper <ryanh@us.ibm.com>
> > ---
> >  blockdev.c      |   39 +++++++++++++++++++++++++++++++++++++++
> >  blockdev.h      |    1 +
> >  hmp-commands.hx |   18 ++++++++++++++++++
> >  3 files changed, 58 insertions(+), 0 deletions(-)
> > 
> > diff --git a/blockdev.c b/blockdev.c
> > index 6cb179a..f6ac439 100644
> > --- a/blockdev.c
> > +++ b/blockdev.c
> > @@ -14,6 +14,8 @@
> >  #include "qemu-option.h"
> >  #include "qemu-config.h"
> >  #include "sysemu.h"
> > +#include "hw/qdev.h"
> > +#include "block_int.h"
> >  
> >  static QTAILQ_HEAD(drivelist, DriveInfo) drives = QTAILQ_HEAD_INITIALIZER(drives);
> >  
> > @@ -597,3 +599,40 @@ int do_change_block(Monitor *mon, const char *device,
> >      }
> >      return monitor_read_bdrv_key_start(mon, bs, NULL, NULL);
> >  }
> > +
> > +int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
> > +{
> > +    const char *id = qdict_get_str(qdict, "id");
> > +    BlockDriverState *bs;
> > +    BlockDriverState **ptr;
> > +    Property *prop;
> > +
> > +    bs = bdrv_find(id);
> > +    if (!bs) {
> > +        qerror_report(QERR_DEVICE_NOT_FOUND, id);
> > +        return -1;
> > +    }
> > +
> > +    /* quiesce block driver; prevent further io */
> > +    qemu_aio_flush();
> > +    bdrv_flush(bs);
> > +    bdrv_close(bs);
> > +
> > +    /* clean up guest state from pointing to host resource by
> > +     * finding and removing DeviceState "drive" property */
> > +    for (prop = bs->peer->info->props; prop && prop->name; prop++) {
> > +        if (prop->info->type == PROP_TYPE_DRIVE) {
> > +            ptr = qdev_get_prop_ptr(bs->peer, prop);
> > +            if ((*ptr) == bs) {
> > +                bdrv_detach(bs, bs->peer);
> > +                *ptr = NULL;
> > +                break;
> > +            }
> > +        }
> > +    }
> > +
> > +    /* clean up host side */
> > +    drive_uninit(drive_get_by_blockdev(bs));
> > +
> > +    return 0;
> > +}
> > diff --git a/blockdev.h b/blockdev.h
> > index 653affc..2a0559e 100644
> > --- a/blockdev.h
> > +++ b/blockdev.h
> > @@ -51,5 +51,6 @@ int do_eject(Monitor *mon, const QDict *qdict, QObject **ret_data);
> >  int do_block_set_passwd(Monitor *mon, const QDict *qdict, QObject **ret_data);
> >  int do_change_block(Monitor *mon, const char *device,
> >                      const char *filename, const char *fmt);
> > +int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
> >  
> >  #endif
> > diff --git a/hmp-commands.hx b/hmp-commands.hx
> > index e5585ba..d6dc18c 100644
> > --- a/hmp-commands.hx
> > +++ b/hmp-commands.hx
> > @@ -68,6 +68,24 @@ Eject a removable medium (use -f to force it).
> >  ETEXI
> >  
> >      {
> > +        .name       = "drive_del",
> > +        .args_type  = "id:s",
> > +        .params     = "device",
> > +        .help       = "remove host block device",
> > +        .user_print = monitor_user_noop,
> > +        .mhandler.cmd_new = do_drive_del,
> > +    },
> > +
> > +STEXI
> > +@item delete @var{device}
> > +@findex delete
> 
> I think this should be @item drive_del and @findex drive_del.

Yep.

> 
> Kevin

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com