linux-kernel - Re: [PATCH] scsi:iscsi: Record session's startup mode in kernel

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Date:   Wed, 23 Nov 2022 01:45:08 +0800
From:   Wenchao Hao <haowenchao22@...il.com>
To:     Mike Christie <michael.christie@...cle.com>
Cc:     Wenchao Hao <haowenchao@...wei.com>, Lee Duncan <lduncan@...e.com>,
        Chris Leech <cleech@...hat.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        open-iscsi@...glegroups.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, liuzhiqiang26@...wei.com,
        linfeilong@...wei.com
Subject: Re: [PATCH] scsi:iscsi: Record session's startup mode in kernel

On Wed, Nov 23, 2022 at 1:27 AM Mike Christie
<michael.christie@...cle.com> wrote:
>
> On 11/22/22 3:30 PM, Wenchao Hao wrote:
> > There are 3 iscsi session's startup mode which are onboot, manual and
> > automatic. We can boot from iSCSI disks with help of dracut's service
> > in initrd, which would set node's startup mode to onboot, then create
> > iSCSI sessions.
> >
> > While the configure of onboot mode is recorded in file of initrd stage
> > and would be lost when switch to rootfs. Even if we update the startup
> > mode to onboot by hand after switch to rootfs, it is possible that the
> > configure would be covered by another discovery command.
> >
> > root would be mounted on iSCSI disks when boot from iSCSI disks, if the
> > sessions is logged out, the related disks would be removed, which would
> > cause the whole system halt.
>
> The userspace tools check for this already don't they? Running iscsiadm
> on the root disk returns a failure and message about it being in use.
>

It seems we did not check.

> Userspace can check the session's disks and see if they are mounted and
> what they are being used for.

It's hard to check if iSCSI disk is in used. If iSCSI disk is used to
build multipath device mapper,
, and lvm is built on these dm devices, the root is mounted on these
lvm devices, like following:

sde                                       8:64   0   60G  0 disk
└─360014051a174917ce514486bca53b324 253:4    0   60G  0 mpath
  ├─lvm-root                     253:0    0 38.3G  0 lvm   /
  ├─lvm-swap                   253:1    0  2.1G  0 lvm   [SWAP]
  └─lvm-home                  253:2    0 18.7G  0 lvm   /home

It's too coupling to check these dm devices.