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Message-ID: <c4f4bc15-09b7-ffee-8e56-c857fc1431a1@huawei.com>
Date:   Sat, 6 May 2023 17:57:13 +0800
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Subject: Re: [PATCH v2] ata: libata-scsi: Fix get identity data failed
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To:     John Garry <john.g.garry@oracle.com>,
        Damien Le Moal <dlemoal@kernel.org>, <jejb@linux.ibm.com>,
        <martin.petersen@oracle.com>, <damien.lemoal@opensource.wdc.com>
CC:     <linux-scsi@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linuxarm@huawei.com>, <prime.zeng@hisilicon.com>,
        <kangfenglong@huawei.com>
References: <20230505025712.19438-1-yangxingui@huawei.com>
 <291f1d97-9195-45ac-8e12-058f5c797277@kernel.org>
 <b13c9445-39c5-f207-d5d0-d6c86eee54ae@oracle.com>
 <1b703656-e966-63f8-19dd-33e4e9914676@huawei.com>
 <cae0ac63-f391-08c0-c646-23037485c189@oracle.com>
From:   yangxingui <yangxingui@huawei.com>
In-Reply-To: <cae0ac63-f391-08c0-c646-23037485c189@oracle.com>
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On 2023/5/5 17:51, John Garry wrote:
> On 05/05/2023 10:14, yangxingui wrote:
>>> hmmm... is it really acceptable that libata is referencing libsas? I 
>>> didn't think that it would be. libsas uses libata, not the other way 
>>> around.
>> Yeah, I didn't expect that either. Is there any other way? If so, is 
>> patch v1 OK?
> 
> I still think that we can do better than v1.
OK
> 
>>>
>>>>>   #include <linux/libata.h>
>>>>>   #include <linux/hdreg.h>
>>>>>   #include <linux/uaccess.h>
>>>>> @@ -2745,10 +2746,17 @@ static struct ata_device 
>>>>> *__ata_scsi_find_dev(struct ata_port *ap,
>>>>>    *    Associated ATA device, or %NULL if not found.
>>>>>    */
>>>>>   struct ata_device *
>>>>> -ata_scsi_find_dev(struct ata_port *ap, const struct scsi_device 
>>>>> *scsidev)
>>>> Why drop the const ?
>>>>
>>>>> +ata_scsi_find_dev(struct ata_port *ap, struct scsi_device *scsidev)
>>>>>   {
>>>>> -    struct ata_device *dev = __ata_scsi_find_dev(ap, scsidev);
>>>>> +    struct ata_device *dev;
>>>>> +
>>>>> +    if (ap->flags & ATA_FLAG_SAS_HOST) {
>>>
>>> And this is SAS host. Not necessarily libsas (even though with ipr 
>>> libata usage gone, it would be the only user).
>> Add a new flag only for libsas?
> 
> No, because of previous reason.
> 
> Please remind me - at what point do we error within ata_scsi_find_dev() 
> and return NULL for a libsas host?
The scsi_host_template filled by libsas and call ata_scsi_find_dev() has 
this problem. After sas_change_queue_depth() is fixed, only sas_ioctl() 
has this problem now.
> 
> Note: it would be good to include that commit message for future reference.
> 
> Maybe we could add a method to ata_port_operations to do this lookup. I 
> assume that is abusing ata_port_operations purpose, since it's mostly 
> for HW methods.
> 
> Or do we actually use sdev->hostdata for libata or libsas? If not, maybe 
> we could store the struct ata_device pointer there.
Well, it might be a way.

Thanks,
Xingui
.
> 
> I'm just thinking out loud now...
> 
> Thanks,
> John
> 
> 
> .