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From:   Ryusuke Konishi <konishi.ryusuke@gmail.com>
Date:   Thu, 7 Apr 2022 02:28:15 +0900
Message-ID: <CAKFNMokGOma3pvHdEsnsjuKgW+jpYX9zx8fWwJWyeKuCpKz-YQ@mail.gmail.com>
Subject: Re: [PATCH 23/27] block: add a bdev_max_discard_sectors helper
To:     Christoph Hellwig <hch@lst.de>
Cc:     Andreas Gruenbacher <agruenba@redhat.com>,
        Jens Axboe <axboe@kernel.dk>,
        device-mapper development <dm-devel@redhat.com>,
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On Wed, Apr 6, 2022 at 11:05 PM Christoph Hellwig <hch@lst.de> wrote:
>
> Add a helper to query the number of sectors support per each discard bio
> based on the block device and use this helper to stop various places from
> poking into the request_queue to see if discard is supported and if so how
> much.  This mirrors what is done e.g. for write zeroes as well.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
...
> diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
> index 16e775bcf4a7c..7d510e4231713 100644
> --- a/drivers/target/target_core_device.c
> +++ b/drivers/target/target_core_device.c
> @@ -829,9 +829,7 @@ struct se_device *target_alloc_device(struct se_hba *hba, const char *name)
>  }
>
>  /*
> - * Check if the underlying struct block_device request_queue supports
> - * the QUEUE_FLAG_DISCARD bit for UNMAP/WRITE_SAME in SCSI + TRIM
> - * in ATA and we need to set TPE=1

> + * Check if the underlying struct block_device request_queue supports disard.
>   */

Here was a typo:

 s/disard/discard/

On Thu, Apr 7, 2022 at 12:19 AM Andreas Gruenbacher <agruenba@redhat.com> wrote:
> If I'm misreading things, could you please document that
> bdev_max_discard_sectors() != 0 implies that discard is supported?

I got the same impression.   Checking the discard support with
bdev_max_discard_sectors() != 0 seems a bit unclear than before.

Thanks,
Ryusuke Konishi