[PATCH v3] nvmet: avoid unnecessary flush bio

[Guixin Liu]

Hi,

Gentle ping.

thanks,

Guixin Liu

在 2022/7/29 11:53, Guixin Liu 写道:
> For no volatile write cache block device backend, sending flush bio is
> unnecessary, avoid to do that.
>
> Signed-off-by: Guixin Liu <kanie at linux.alibaba.com>
> ---
>
> Changes on v3:
> - Remove file backend change.
>
> Changes on v2:
> - Use bdev_write_cache instead of open code.
> - Use NVME_SC_SUCCESS instead of translation, and remove "else".
>
> Test log:
> - Add printk log at new if branch.
> - Use nvme_loop to emulate nvme device.
> - Use tcm_loop and tcmu to emulate no volatile write cache block backend
>    by setting emulate_write_cache=0.
> - Send "nvme flush /dev/nvme0n1", there is a log print, and cmd return success.
> - Send "nvme set-feature /dev/nvme0n1 --namespace-id=1 --feature-id=0x84 --value=1",
>    there is a log print, and cmd return success.
> - Format nvme0n1 to ext4 filesystem, then create a file, write data and save, there
>    is a log print, and no error.
>
>   drivers/nvme/target/io-cmd-bdev.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
> index 2dc1c10..8d527a8 100644
> --- a/drivers/nvme/target/io-cmd-bdev.c
> +++ b/drivers/nvme/target/io-cmd-bdev.c
> @@ -334,6 +334,11 @@ static void nvmet_bdev_execute_flush(struct nvmet_req *req)
>   {
>   	struct bio *bio = &req->b.inline_bio;
>   
> +	if (!bdev_write_cache(req->ns->bdev)) {
> +		nvmet_req_complete(req, NVME_SC_SUCCESS);
> +		return;
> +	}
> +
>   	if (!nvmet_check_transfer_len(req, 0))
>   		return;
>   
> @@ -347,6 +352,9 @@ static void nvmet_bdev_execute_flush(struct nvmet_req *req)
>   
>   u16 nvmet_bdev_flush(struct nvmet_req *req)
>   {
> +	if (!bdev_write_cache(req->ns->bdev))
> +		return 0;
> +
>   	if (blkdev_issue_flush(req->ns->bdev))
>   		return NVME_SC_INTERNAL | NVME_SC_DNR;
>   	return 0;