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Subject: Re: [PATCH] drivers/ata: print trim features at device initialization
To:     James Bottomley <James.Bottomley@HansenPartnership.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Christoph Hellwig <hch@infradead.org>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-ide@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
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 <b554c428-417e-5fef-1776-87a4db1d674a@yandex-team.ru>
 <1560206933.3698.27.camel@HansenPartnership.com>
From:   Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Message-ID: <cd91b050-cbc6-7c3b-f9f8-91c0760668e6@yandex-team.ru>
Date:   Fri, 14 Jun 2019 16:49:37 +0300
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On 11.06.2019 1:48, James Bottomley wrote:
> On Mon, 2019-06-10 at 10:49 +0300, Konstantin Khlebnikov wrote:
>> On 10.06.2019 0:37, James Bottomley wrote:
>>> On Sat, 2019-06-08 at 17:13 +0300, Konstantin Khlebnikov wrote:
>>>>> On 08.06.2019 11:25, Christoph Hellwig wrote:> On Fri, Jun 07,
>>>>> 2019
>>>>> at 10:34:39AM +0300, Konstantin Khlebnikov wrote:
>>>>>    >
>>>>>    > Do we really need to spam dmesg with even more ATA
>>>>> crap?  What
>>>>> about
>>>>>    > a sysfs file that can be read on demand instead?
>>>>>    >
>>>>>
>>>>> Makes sense.
>>>>>
>>>>> Trim state is exposed for ata_device:
>>>>> /sys/class/ata_device/devX.Y/trim
>>>>> but there is no link from scsi device to ata device so they
>>>>> hard to match.
>>>>>
>>>>> I'll think about it.
>>>>
>>>> Nope. There is no obvious way to link scsi device with
>>>> ata_device. ata_device is built on top of "transport_class" and
>>>> "attribute_container". This some extremely over engineered sysfs
>>>> framework used only in ata/scsi. I don't want to touch this.
>>>
>>> You don't need to know any of that.  The problem is actually when
>>> the ata transport classes were first created, the devices weren't
>>> properly parented.  What should have happened, like every other
>>> transport class, is that the devices should have descended down to
>>> the scsi device as the leaf in an integrated fashion.  Instead,
>>> what we seem to have is three completely separate trees.
>>>
>>> So if you look at a SAS device, you see from the pci device:
>>>
>>> host2/port-2:0/end_device-2:0/target2:0:0/2:0:0:0/block/sdb/sdb1
>>>
>>> But if you look at a SATA device, you see three separate paths:
>>>
>>> ata3/host3/target3\:0\:0/3\:0\:0\:0/block/sda/sda1
>>> ata3/link3/dev3.0/ata_device/dev3.0
>>> ata3/ata_port/ata3
>>>
>>> Instead of an integrated tree
>>>
>>> Unfortunately, this whole thing is unfixable now.  If I integrate
>>> the tree properly, the separate port and link directories will get
>>> subsumed and we won't be able to recover them with judicious
>>> linking so scripts relying on them will break.  The best we can
>>> probably do is add additional links with what we have.
>>>
>>> To follow the way we usually do it, there should be a link from the
>>> ata device to the scsi target, but that wouldn't help you find the
>>> "trim" files, so it sounds like you want a link from the scsi
>>> device to the ata device, which would?
>>
>> Yes, I'm talking about link from scsi device to leaf ata_device node.
>>
>> In libata scsi_device has one to one relation with ata_device.
>> So making link like /sys/class/block/sda/device/ata_device should be
>> possible easy.
>> But I haven't found implicit reference from struct ata_device to
>> ata_device in sysfs.
> 
> If that's all you want, it is pretty simple modulo the fact we can only
> get at the tdev, not the lower transport device, which is what you
> want, but at least it's linear from the symlink.
> 
> The attached patch should do this.
> 
> Now I see this for my non-sas device:
> 
> # ls -l /sys/class/scsi_device/3\:0\:0\:0/device/ata_device
> lrwxrwxrwx 1 root root 0 Jun 10 13:39 /sys/class/scsi_device/3:0:0:0/device/ata_device -> ../../../link3/dev3.0

I've tried this too. Such link is not very useful,
because attribute 'trim' is deeper and suffix path isn't constant:

/sys/class/block/sda/device/ata_device/ata_device/dev1.0/trim

while I expect something like

/sys/class/block/sda/device/ata_device/trim

> 
> James
> 
> ---
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 391ac0503dc0..b644336a6d65 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -4576,7 +4576,20 @@ void ata_scsi_scan_host(struct ata_port *ap, int sync)
>   			sdev = __scsi_add_device(ap->scsi_host, channel, id, 0,
>   						 NULL);
>   			if (!IS_ERR(sdev)) {
> +				int r;
> +
>   				dev->sdev = sdev;
> +				/* this is a sysfs stupidity: we don't
> +				 * care if the link actually gets
> +				 * created: there's no error handling
> +				 * for failure and we continue on
> +				 * regardless, but we have to discard
> +				 * the return value like this to
> +				 * defeat unused result checking */
> +				r = sysfs_create_link(&sdev->sdev_gendev.kobj,
> +						      &dev->tdev.kobj,
> +						      "ata_device");
> +				(void)r;
>   				scsi_device_put(sdev);
>   			} else {
>   				dev->sdev = NULL;
> @@ -4703,6 +4716,7 @@ static void ata_scsi_remove_dev(struct ata_device *dev)
>   		ata_dev_info(dev, "detaching (SCSI %s)\n",
>   			     dev_name(&sdev->sdev_gendev));
>   
> +		sysfs_remove_link(&sdev->sdev_gendev.kobj, "ata_device");
>   		scsi_remove_device(sdev);
>   		scsi_device_put(sdev);
>   	}
>