[Qemu-devel] Re: [PATCH 0/5] Fix migration with NFS & iscsi/Fiber channel

[Juan Quintela]

Juan Quintela <address@hidden> wrote:
> Hi

Nack myself :-(

After discussions with hch on irc, he "convinced" me that only way to
fix the problem is forcing O_DIRECT if migration is going to happen.

So, changing patchset to check that cache=none is used in all read/write
devices.

Later, Juan.

> This patch set creates infrastructure to invalidate buffers on
> migration target machine.  The best way to see the problems is:
>
> # create a new qcow2 image
> qemu-img create -f qcow2 foo.img
> # start the destination host
> qemu .... path=foo.img....
> # start the source host with one installation
> qemu .... path=foo.img....
> # migrate after lots of disk writes
>
> Destination will have "read" the beggining of the blocks of the file
> (where the headers are).  There are two bugs here:
> a- we need to re-read the image after migration, to have the new values
>    (reopening fixes it)
> b- we need to be sure that we read the new blocks that are on the server,
>    not the buffered ones locally from the start of the run.
>    NFS: flush on source and close + open on target invalidates the cache
>    Block devices: on linux, BLKFLSBUF invalidates all the buffers for that
>    device.  This fixes iSCSI & FiberChannel.
>
> I tested iSCSI & NFS.  NFS patch have been on RHEL5 kvm forever (I just
> forget to send the patch upstream).  Our NFS gurus & cluster gurus told
> that this is enough for linux to ensure consistence.
>
> Once there, I fixed a couple of minor bugs (the first 3 patches):
> - migration should exit with error 1 as everything else.
> - memory leak on drive_uninit.
> - fix cleanup on error on drive_init()
>
> Later, Juan.
>
> Juan Quintela (5):
>   migration: exit with error code
>   blockdev: don't leak id on removal
>   blockdev: release resources in the error case
>   Reopen files after migration
>   drive_open: Add invalidate option for block devices
>
>  block.h           |    2 ++
>  block/raw-posix.c |   24 ++++++++++++++++++++++++
>  blockdev.c        |   53 
> +++++++++++++++++++++++++++++++++++++++++++++--------
>  blockdev.h        |    6 ++++++
>  migration.c       |    8 +++++++-
>  vl.c              |    2 +-
>  6 files changed, 85 insertions(+), 10 deletions(-)