[Qemu-devel] [PATCH V2 0/4] ide: avoid main-loop hang on CDROM/NFS failure

[Peter Lieven]

This series aims at avoiding a hanging main-loop if a vserver has a
CDROM image mounted from a NFS share and that NFS share goes down.
Typical situation is that users mount an CDROM ISO to install something
and then forget to eject that CDROM afterwards.
As a consequence this mounted CD is able to bring down the
whole vserver if the backend NFS share is unreachable. This is bad
especially if the CDROM itself is not needed anymore at this point.

This series aims at fixing 2 blocking I/O operations that would
hang if the NFS server is unavailable:
 - ATAPI PIO read requests used sync calls to blk_read, convert
   them to an async variant where possible.
 - If a busmaster DMA request is cancelled all requests are drained.
   Convert the drain to an async request canceling.

v1->v2: - fix offset for 2352 byte sector size [Kevin]
        - use a sync request if we continue an elementary transfer.
          As John pointed out we enter a race condition between next
          IDE command and async transfer otherwise. This is sill not
          optimal, but it fixes the NFS down problems for all cases where
          the NFS server goes down while there is no PIO CD activity.
          Of course, it could still happen during a PIO transfer, but I
          expect this to be the unlikelier case.
          I spent some effort trying to read more sectors at once and
          avoiding continuation of elementary transfers, but with
          whatever I came up it was destroying migration between different
          Qemu versions. I have a quite hackish patch that works and
          should survive migration, but I am not happy with it. So I
          would like to start with this version as it is a big improvement
          already.
        - Dropped Patch 5 because it is upstream meanwhile.

Peter Lieven (4):
  ide/atapi: make PIO read requests async
  ide/atapi: blk_aio_readv may return NULL
  ide: add support for cancelable read requests
  ide/atapi: enable cancelable requests

 hw/ide/atapi.c    | 99 +++++++++++++++++++++++++++++++++++++++++++++++++------
 hw/ide/core.c     | 55 +++++++++++++++++++++++++++++++
 hw/ide/internal.h | 16 +++++++++
 hw/ide/pci.c      | 42 +++++++++++++++--------
 4 files changed, 188 insertions(+), 24 deletions(-)

-- 
1.9.1