this variable is a helper to tell libiscsi to not reset the nops_in_flight
on receival of a NOP-Out if the oldest element in the waitpdu queue is
not changed since the last NOP-Out.
The idea is that we can detect a command that the target silently dropped
by this mechanism and run into a NOP timeout forcing a reconnect.
This environment variable is not suitable if a command is send that is taking more than
the allowed timeout for a NOP-Out as a reply to a initiator generated NOP-In
(or several NOP-Outs if more than 1 in flight is allowed).
Signed-off-by: Peter Lieven <pl@kamp.de>
originally NOPs where used to detect failures in the transport
layer. This is e.g. implemented in qemu since a few years now.
Recently I found a few vServers with hanging I/O where
the NOP mechanism could not detect the error.
The reason is most likely due to a bug in the target,
however if NOPs increase the CmdSN this could help
to detect such failures. If there are requests hanging
and the OS stops I/O before CmdSN > MaxCmdSN we can currently
send NOPs forever and they might still be answered. If
a NOP increases the CmdSN we will enter a point where CmdSN
is greater than MaxCmdSN. This is, of course, not the ideal check,
but it might detect some types of errors. Ideally we would
send out a Test-Unit-Ready command with attr=ordered, but
that requires a new API and/or modification of the tool
that uses libiscsi. This here comes with no modification for
the userspace.
Signed-off-by: Peter Lieven <pl@kamp.de>
Remove iscsi_allocate_pdu() which is just a wrapper.
Rename iscsi_allocate_pdu_with_itt_flags() to iscsi_allocate_pdu()
and update all callers.
This only removes a wrapper function and contains no logic changes.
Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
This patch adds the abilitiy to libiscsi to count the number
of consecutive outstanding NOPs.
With this ability its fairly easy to implement a keepalive
check with NOPs in your application.
Periodically (e.g. every 5 secs) create a NOP-Out with:
iscsi_nop_out_async(iscsi, NULL, NULL, 0, NULL);
At that time check the number of consecutive missing NOP-Ins
with
iscsi_get_nops_in_flight(iscsi) > N.
Where N is the number of missing NOP-Ins you will allow.
Please note that it is legitime for the Target to ignore
a NOP if the load is very high as those packet are mark
as IMMEDIATE.
Signed-off-by: Peter Lieven <pl@kamp.de>
Just like DATA_OUT we should just discard NOPs instead of requeueing them
on session reconnect.
Add new flag that to indicate this behaviour on reconnect and set it for
both data out and nops
It is not real zero-copy since the data is still copied in the kernel,
but it avoids copying the data inside libiscsi as well as in the callback.
For SCSI tasks that will return data from the target, the application can now
specify application buffers for libiscsi to read the data directly into.
This is done by calling scsi_task_add_data_in_buffer(task, ...
These buffers need not be linear, you can specify different areas to read into
by calling this function several times.
See examples/iscsiclient.c for an example.
Input processing used to keep all data in one single input buffer, which
makes it hard to handle nested events as well as reading directly from the
socket into the application buffer without an extra copy.
Create a new iscsi_in_pdu structure where we store the header, and any data
for the recevied pdu and store them in a proper input queue.
Change the signature for all processing functions to tahe a iscsi_in_pdu
structure for the received pdu instead of just a pointer to a buffer.
