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nop: clear immediate flag in iscsi_nop_out_async

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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>
This commit is contained in:
Peter Lieven
2015-03-27 09:53:23 +01:00
parent cb6667a5dc
commit 5c4bd85b80
1 changed files with 3 additions and 6 deletions
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9
lib/nop.c
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@@ -46,9 +46,6 @@ iscsi_nop_out_async(struct iscsi_context *iscsi, iscsi_command_cb cb,
return -1;
}
/* immediate flag */
iscsi_pdu_set_immediate(pdu);
/* flags */
iscsi_pdu_set_pduflags(pdu, 0x80);
@@ -58,12 +55,11 @@ iscsi_nop_out_async(struct iscsi_context *iscsi, iscsi_command_cb cb,
/* lun */
iscsi_pdu_set_lun(pdu, 0);
/* cmdsn is not increased if Immediate delivery*/
iscsi_pdu_set_cmdsn(pdu, iscsi->cmdsn);
pdu->cmdsn = iscsi->cmdsn;
pdu->cmdsn = iscsi->cmdsn++;
/* exp statsn */
iscsi_pdu_set_expstatsn(pdu, iscsi->statsn+1);
iscsi_pdu_set_expstatsn(pdu, iscsi->statsn + 1);
pdu->callback = cb;
pdu->private_data = private_data;
@@ -141,6 +137,7 @@ iscsi_process_nop_out_reply(struct iscsi_context *iscsi, struct iscsi_pdu *pdu,
ISCSI_LOG(iscsi, (iscsi->nops_in_flight > 1) ? 1 : 6, "NOP Out Reply received");
iscsi_adjust_maxexpcmdsn(iscsi, in);
iscsi->nops_in_flight = 0;
if (pdu->callback == NULL) {