[PATCH 1/2] erofs-utils: mount: gracefully exit when `erofsmount_nbd()` encounts an error

[Gao Xiang]

Hi Yifan,

On 2025/12/16 16:05, Yifan Zhao wrote:
> If the main process of `erofsmount_nbd()` encounters an error after the
> nbd device has been successfully set up, it fails to disconnect it
> before exiting, resulting in the subprocess not being cleaned up and
> blocked on `ioctl(nbdfd, NBD_DO_IT, 0)`.

Do you have a simple test case (IOWs, how do you test this?)
And is it possible to move the test case to erofs-utils tests?

> 
> This patch resolves the issue by invoking `erofs_nbd_disconnect()`
> before exiting on error.

See below.

> 
> Signed-off-by: Yifan Zhao <zhaoyifan28 at huawei.com>
> ---
>   lib/liberofs_nbd.h | 2 +-
>   mount/main.c       | 8 ++++++++
>   2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/liberofs_nbd.h b/lib/liberofs_nbd.h
> index 260605a..93daa24 100644
> --- a/lib/liberofs_nbd.h
> +++ b/lib/liberofs_nbd.h
> @@ -28,7 +28,7 @@ struct erofs_nbd_request {
>   		char   handle[8];	/* older spelling of cookie */
>   	};
>   	u64 from;
> -        u32 len;
> +	u32 len;
>   } __packed;
>   
>   /* 30-day timeout for NBD recovery */
> diff --git a/mount/main.c b/mount/main.c
> index 758e8f8..a093167 100644
> --- a/mount/main.c
> +++ b/mount/main.c
> @@ -1206,6 +1206,14 @@ static int erofsmount_nbd(struct erofs_nbd_source *source,
>   				free(id);
>   		}
>   	}
> +
> +	if (err < 0) {
> +		nbdfd = open(nbdpath, O_RDWR);

I'm not sure if it's a best-practice (is it possible
nbdpath can be reused?)

Could we just kill the subprocess instead?

Also ioctl is discouraged and netlink is preferred now.

Thanks,
Gao Xiang

> +		if (nbdfd > 0) {
> +			erofs_nbd_disconnect(nbdfd);
> +			close(nbdfd);
> +		}
> +	}
>   	return err;
>   }
>