Am 26.11.2019 um 19:19 hat Tony Asleson geschrieben: > On 11/21/19 4:30 AM, Stefan Hajnoczi wrote: > > blkdebug can inject EIO when a specific LBA is accessed. Is that > > enough for what you want to do? Then you can reuse and maybe extend > > blkdebug. > > Not exactly. For SCSI, I would like to be able to return different > types of device errors on reads eg. 03/1101, 03/1600 and writes. The > SCSI sense data needs to include the first block in error for the > transfer. It would be good to also have the ability to include things > like SCSI check conditions with recoverable errors too. > > I've been experimenting with blkdebug, to learn more and to see how it > would need to be extended. One thing that I was trying to understand is > how an EIO from blkdebug gets translated into a bus/device specific > error. At the moment I'm not sure. I've been trying to figure out the > layering. I think that blkdebug sits between the device specific model > and the underlying block representation on disk. Thus it injects error > return values when accessing the underlying data, but that could be > incorrect. If it is correct I should see some code that translates the > EIO to something transport/device specific.
The point where the device calls into the generic block layer is where the functions that start with blk_ are called (blk_aio_pwritev() and blk_aio_preadv() are probably the most interesting ones). The callback path in scsi-disk is not that easy to follow, but in the end, error returns should result in scsi_handle_rw_error() being called where error codes are translated into SCSI sense codes. > Although I don't understand how returning an ENOSPC from read_aio in > blkdebug would get translated for a SCSI disk as it doesn't make sense > to me (one of the examples in the documentation). Actually I don't > know how getting ENOSPC on a read could happen? That scenario doesn't make a lot of sense to me either, but blkdebug can just inject any error code, even nonsensical ones. > During my blkdebug experimentation, I've been using lsi53c895a with > scsi-disk and thus far I've not been able to generate a read error back > to the guest kernel. I've managed to abort qemu with an assert and hang > qemu without being able to get an error back to the guest kernel. I > wrote up one of them: https://bugs.launchpad.net/qemu/+bug/1853898 . > Specifying a specific sector hasn't worked for me yet. I'm still trying > to figure out how to enable tracing/debugging etc. to see what I'm going > incorrectly. Note that depending on the rerror/werror options, QEMU may not deliver errors to the guest, but stop VMs instead. If the monitor is still responsive, it's likely that you just got a stopped VM rather than a hanging QEMU. The default is that the VM is stopped for ENOSPC and other errors are delivered to the guest. Kevin
