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Date:   Tue, 26 Sep 2023 00:26:26 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Mike Christie <michael.christie@oracle.com>
Cc:     Wenchao Hao <haowenchao2@huawei.com>,
        Christoph Hellwig <hch@infradead.org>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, Hannes Reinecke <hare@suse.de>,
        linux-kernel@vger.kernel.org, louhongxiang@huawei.com,
        lixiaokeng@huawei.com
Subject: Re: [RFC PATCH v2 00/18] scsi: scsi_error: Introduce new error
 handle mechanism
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On Mon, Sep 25, 2023 at 12:54:48PM -0500, Mike Christie wrote:
> I think we want to figure out Hannes's patches first.

Yes.

> For a new EH design we will want to be able to do multiple TMFs in parallel
> on the same host/target right? 
> 
> The problem is that we need to be able to make forward progress in the EH
> path and not fail just because we can't allocate memory for a TMF related
> struct. To accomplish this now, drivers will use mempools, preallocate TMF
> related structs/mem/tags with their scsi_cmnd related structs, preallocate
> per host/target/device related structs or ignore what I wrote above and just
> fail.
> 
> Hannes's patches fix up the eh callouts so they don't pass in a scsi_cmnd
> when it's not needed. That seems nice because after that, then for your new
> EH we can begin to standardize on how to handle preallocation of drivers
> resources needed to perform TMFs for your new EH. It could be a per
> device/target/host callout to allow drivers to preallocate, then scsi-ml calls
> into the drivers with that data. It doesn't have to be exactly like that or
> anything close. It would be nice for drivers to not have to think about this
> type of thing and scsi-ml just to handle the resource management for us when
> there are multiple TMFs in progress.

Exactly!