[Devel] [PATCH] target: don't call an unmap callback if a range length is zero

[Konstantin Khorenko]

i've filed a bug for this issue: https://jira.sw.ru/browse/PSBM-79534

Andrey, please, post the usecase when we faced fallocating 0 range - to the bug at least,
otherwise in a year we'll forget about the reason completely.

Thank you.

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 12/14/2017 12:23 AM, Andrei Vagin wrote:
> If a length of a range is zero, it means there is nothing to unmap
> and we can skip this range.
>
> Here is one more reason, why we have to skip such ranges.  An unmap
> callback calls file_operations->fallocate(), but the man page for the
> fallocate syscall says that fallocate(fd, mode, offset, let) returns
> EINVAL, if len is zero. It means that file_operations->fallocate() isn't
> obligated to handle zero ranges too.
>
> Cc: Alexey.Kuznetsov at acronis.com
> ---
>  drivers/target/target_core_sbc.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
> index 59a1235..99fb25f 100644
> --- a/drivers/target/target_core_sbc.c
> +++ b/drivers/target/target_core_sbc.c
> @@ -1132,9 +1132,11 @@ sbc_execute_unmap(struct se_cmd *cmd,
>  			goto err;
>  		}
>
> -		ret = do_unmap_fn(cmd, priv, lba, range);
> -		if (ret)
> -			goto err;
> +		if (range) {
> +			ret = do_unmap_fn(cmd, priv, lba, range);
> +			if (ret)
> +				goto err;
> +		}
>
>  		ptr += 16;
>  		size -= 16;
>