iscsi: add iscsi_create support

This patch adds support for bdrv_create. This allows e.g.
to use qemu-img to convert from any supported device to
an iscsi backed storage as destination.

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
iscsi: partly avoid iovec linearization in iscsi_aio_writev

libiscsi expects all write16 data in a linear buffer. If the
iovec only contains one buffer we can skip the linearization
step as well as the additional malloc/free and pass the
buffer directly.

Reported-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
iscsi: add support for iSCSI NOPs [v2]

This patch will send NOP-Out PDUs every 5 seconds to the iSCSI target.
If a consecutive number of NOP-In replies fail a reconnect is initiated.
iSCSI NOPs help to ensure that the connection to the target is still operational.
This should not, but in reality may be the case even if the TCP connection is still
alive if there are bugs in either the target or the initiator implementation.

v2:
 - track the NOPs inside libiscsi so libiscsi can reset the counter
   in case it initiates a reconnect.

Signed-off-by: Peter Lieven <pl@kamp.de>
scsi: fix segfault with 0-byte disk

When a 0-sized disk is found, READ CAPACITY will return a
LUN NOT READY error.  However, because it returns -1 instead
of zero, the HBA will call scsi_req_continue.  This will
typically cause a segmentation fault or an assertion failure.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
lsi: use qbus_reset_all to reset SCSI bus

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>