iscsi: disable Open-iSCSI login retries

iscsi: disable Open-iSCSI login retries

Since 90c1b10 ("fix #254: iscsi: add support for multipath targets"),
iSCSI storage activation checks whether a session exists for each
discovered portal. If there is a discovered portal without a session,
it performs a discovery and login in the hope of establishing a
session to the portal. If the portal is unreachable when trying to log
in, Open-iSCSI's default behavior is to retry for up to 2 minutes, as
explained in /etc/iscsi/iscid.conf:

> # The default node.session.initial_login_retry_max is 8 and
> # node.conn[0].timeo.login_timeout is 15 so we have:
> #
> # node.conn[0].timeo.login_timeout * \
> node.session.initial_login_retry_max = 120s

If pvestatd is activating the storage, it will be blocked during that
time, which is undesirable. This is particularly unfortunate if the
target announces portals that the host permanently cannot reach. In
that case, every pvestatd iteration will take 2 minutes. While it can
be argued that such setups are misconfigured, it is still desirable to
keep the fallout of that misconfiguration as low as possible.

In order to reduce the time Open-iSCSI tries to log in, instruct
Open-ISCSI to not perform login retries for that target. For this, set
node.session.initial_login_retry_max for the target to 0. This setting
is stored in Open-iSCSI's records under /etc/iscsi/nodes. As these
records are overwritten with the defaults from /etc/iscsi/iscsid.conf
on discovery, the setting needs to be applied after discovery.

With this setting, one login attempt should take at most 15 seconds.
This is still higher than pvestatd's iteration time of 10 seconds, but
more tolerable. Logins will still be continuously retried by pvestatd
in every iteration until there is a session to each discovered portal.

Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
Tested-by: Mira Limbeck <m.limbeck@proxmox.com>
Reviewed-by: Mira Limbeck <m.limbeck@proxmox.com>