scsi-generic: correct error management

scsi-generic: correct error management

this patch allows to fully use a tape device connected to qemu through
the scsi-generic interface.

Previous patch introduced tape SCSI commands management, this one
improve error case management:

- the SCSI controller command completion must be called with the status
value, not the sense value. In the case of scsi-generic, the SCSI status
is given by the field status of sg_io_hdr_t (the value is left shifted
by one regarding status codes defined in /usr/include/scsi/scsi.h)

- when a read is aborted due to a mark/EOF/EOD/EOM, the len reported to
controller can be 0. LSI controller emulation doesn't know how to manage
this. A workaround found is to call the completion routine with
SCSI_REASON_DONE just after calling it with SCSI_REASON_DATA with len=0.

This patch also manages correctly the block size of the tape device.

This patch has been tested with a real tape device "HP C5683A", linux
guest (debian etch) and tools like "mt", "tar" and "btape".

Windows guest is not better supported than before...

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5497 c046a42c-6fe2-441c-8c8c-71466251a162