linux-kernel - Re: [PATCH v2] scsi: support packing multi-segment in UNMAP command

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Date:   Wed, 15 Jun 2022 06:35:36 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Chao Yu <chao@...nel.org>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] scsi: support packing multi-segment in UNMAP command

On Wed, Jun 15, 2022 at 09:28:46PM +0800, Chao Yu wrote:
> As SPEC describes that it can support unmapping one or more LBA range

s/SPEC/<insert SPC reference here>/

>  {
>  	struct scsi_device *sdp = cmd->device;
>  	struct request *rq = scsi_cmd_to_rq(cmd);
> +	struct bio *bio;
>  	struct scsi_disk *sdkp = scsi_disk(rq->q->disk);
> +	unsigned short segments = blk_rq_nr_discard_segments(rq);
> +	unsigned int data_len = 8 + 16 * segments, i = 0;
>  	char *buf;

Nit: for readability I'd move the bio declaration just above the buf
line.

> +
> +	__rq_for_each_bio(bio, rq) {
> +		u64 lba = sectors_to_logical(sdp, bio->bi_iter.bi_sector);
> +		u32 nr_blocks = sectors_to_logical(sdp, bio_sectors(bio));
> +
> +		put_unaligned_be64(lba, &buf[8 + 16 * i]);
> +		put_unaligned_be32(nr_blocks, &buf[8 + 16 * i + 8]);

Can we have a local variable here?

	unsigned int data_offset = 8;

	....

		put_unaligned_be64(lba, &buf[data_offset]);
		put_unaligned_be64(lba, &buf[data_offset + 8]);
		data_offset += 16;
	}