linux-kernel - Re: [PATCH 01/10] block: introduce BLK_FEAT_WRITE_ZEROES

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Message-ID: <3d749264-6fdd-458f-a3a8-35d2320193b3@huaweicloud.com>
Date: Sat, 14 Jun 2025 12:48:26 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: "Darrick J. Wong" <djwong@...nel.org>, Christoph Hellwig <hch@....de>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-block@...r.kernel.org, dm-devel@...ts.linux.dev,
 linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org,
 linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, tytso@....edu,
 john.g.garry@...cle.com, bmarzins@...hat.com, chaitanyak@...dia.com,
 shinichiro.kawasaki@....com, brauner@...nel.org, martin.petersen@...cle.com,
 yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com,
 yangerkun@...wei.com
Subject: Re: [PATCH 01/10] block: introduce BLK_FEAT_WRITE_ZEROES_UNMAP to
 queue limits features

On 2025/6/13 22:54, Darrick J. Wong wrote:
> On Fri, Jun 13, 2025 at 07:56:30AM +0200, Christoph Hellwig wrote:
>> On Fri, Jun 13, 2025 at 11:15:41AM +0800, Zhang Yi wrote:
>>> Yeah, this solution looks good to me. However, we currently have only
>>> two selections (none and unmap). What if we keep it as is and simply
>>> hide this interface if BLK_FEAT_WRITE_ZEROES_UNMAP is not set, making
>>> it visible only when the device supports this feature? Something like
>>> below:
>>
>> I really hate having all kinds of different interfaces for configurations.
> 
> I really hate the open-coded string parsing nonsense that is sysfs. ;)
> 
>> Maybe we should redo this similar to the other hardware/software interfaces
>> and have a hw_ limit that is exposed by the driver and re-only in
>> sysfs, and then the user configurable one without _hw.  Setting it to
>> zero disables the feature.
> 
> Yeah, that fits the /sys/block/foo/queue model better.
> 

OK, well. Please let me confirm, are you both suggesting adding
max_hw_write_zeores_unmap_sectors and max_write_zeroes_unmap_sectors to
the queue_limits instead of adding BLK_FEAT_WRITE_ZEROES_UNMAP to the
queue_limits->features. Something like the following.

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 378d3a1a22fc..14394850863c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -376,7 +376,9 @@ struct queue_limits {
        unsigned int            max_hw_discard_sectors;
        unsigned int            max_user_discard_sectors;
        unsigned int            max_secure_erase_sectors;
-       unsigned int            max_write_zeroes_sectors;
+       unsigned int            max_hw_write_zeroes_sectors;
+       unsigned int            max_hw_write_zeores_unmap_sectors;
+       unsigned int            max_write_zeroes_unmap_sectors;
        unsigned int            max_hw_zone_append_sectors;
        unsigned int            max_zone_append_sectors;
        unsigned int            discard_granularity;

Besides, we should also rename max_write_zeroes_sectors to
max_hw_write_zeroes_sectors since it is a hardware limitation reported
by the driver.  If the device supports unmap write zeroes,
max_hw_write_zeores_unmap_sectors should be equal to
max_hw_write_zeroes_sectors, otherwise it should be 0.

Right?

Best regards,
Yi.