On Mon, Oct 12, 2015 at 02:27:21PM +0200, Peter Lieven wrote: > 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(-)
Any reason why write and discard requests aren't covered in this series? If this is a good idea for CD-ROM it should be a good idea for all PCI IDE devices. Having a specialized code path is often a sign that it hasn't been tested enough. Can we get confident enough to enable this everywhere?