Re: [PATCH v4]: ublk: Add UBLK_U_CMD_UPDATE_SIZE

[Ming Lei <ming.lei@redhat.com>]

On Wed, Apr 16, 2025 at 01:07:47PM +0300, Jared Holzman wrote:
> Currently ublk only allows the size of the ublkb block device to be
> set via UBLK_CMD_SET_PARAMS before UBLK_CMD_START_DEV is triggered.
> 
> This does not provide support for extendable user-space block devices
> without having to stop and restart the underlying ublkb block device
> causing IO interruption.
> 
> This patch adds a new ublk command UBLK_U_CMD_UPDATE_SIZE to allow the
> ublk block device to be resized on-the-fly.
> 
> Feature flag UBLK_F_UPDATE_SIZE is also added to indicate support for this
> command.
> 
> Signed-off-by: Omri Mann <omri@nvidia.com>
> ---
>  drivers/block/ublk_drv.c      | 18 +++++++++++++++++-
>  include/uapi/linux/ublk_cmd.h |  7 +++++++
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index cdb1543fa4a9..128f094efbad 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -64,7 +64,8 @@
>          | UBLK_F_CMD_IOCTL_ENCODE \
>          | UBLK_F_USER_COPY \
>          | UBLK_F_ZONED \
> -        | UBLK_F_USER_RECOVERY_FAIL_IO)
> +        | UBLK_F_USER_RECOVERY_FAIL_IO \
> +        | UBLK_F_UPDATE_SIZE)
> 
>  #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
>          | UBLK_F_USER_RECOVERY_REISSUE \
> @@ -3067,6 +3068,16 @@ static int ublk_ctrl_get_features(const struct
> ublksrv_ctrl_cmd *header)

I try to apply this patch downloaded from both lore or patchwork, and 'git
am' always complains the patch is broken:

[root@ktest-40 linux]# git am raw
warning: Patch sent with format=flowed; space at the end of lines might be lost.
Applying: ublk: Add UBLK_U_CMD_UPDATE_SIZE
error: corrupt patch at line 11
Patch failed at 0001 ublk: Add UBLK_U_CMD_UPDATE_SIZE
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
[root@ktest-40 linux]# patch -p1 < raw
patching file drivers/block/ublk_drv.c
Hunk #1 FAILED at 64.
patch: **** malformed patch at line 192: ublksrv_ctrl_cmd *header)

Please use 'git-format-patch' to make patch and run `./scripts/checkpatch.pl -g HEAD`
in kernel top directory to make sure no ERROR.

>      return 0;
>  }
> 
> +static void ublk_ctrl_set_size(struct ublk_device *ub, const struct
> ublksrv_ctrl_cmd *header)
> +{
> +    struct ublk_param_basic *p = &ub->params.basic;
> +    u64 new_size = header->data[0];
> +
> +    mutex_lock(&ub->mutex);
> +    p->dev_sectors = new_size;
> +    set_capacity_and_notify(ub->ub_disk, p->dev_sectors);
> +    mutex_unlock(&ub->mutex);
> +}
>  /*
>   * All control commands are sent via /dev/ublk-control, so we have to check
>   * the destination device's permission
> @@ -3152,6 +3163,7 @@ static int ublk_ctrl_uring_cmd_permission(struct
> ublk_device *ub,
>      case UBLK_CMD_SET_PARAMS:
>      case UBLK_CMD_START_USER_RECOVERY:
>      case UBLK_CMD_END_USER_RECOVERY:
> +    case _IOC_NR(UBLK_U_CMD_UPDATE_SIZE):

Here it could be more clean to add one private definition:

	#define UBLK_CMD_UPDATE_SIZE _IOC_NR(UBLK_U_CMD_UPDATE_SIZE)

just like what we did for `UBLK_CMD_DEL_DEV_ASYNC`.

Then use UBLK_CMD_UPDATE_SIZE directly.

>          mask = MAY_READ | MAY_WRITE;
>          break;
>      default:
> @@ -3243,6 +3255,10 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd
> *cmd,
>      case UBLK_CMD_END_USER_RECOVERY:
>          ret = ublk_ctrl_end_recovery(ub, header);
>          break;
> +    case _IOC_NR(UBLK_U_CMD_UPDATE_SIZE):

Same with above.

> +        ublk_ctrl_set_size(ub, header);
> +        ret = 0;
> +        break;
>      default:
>          ret = -EOPNOTSUPP;
>          break;
> diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
> index 583b86681c93..587a54b3cfe1 100644
> --- a/include/uapi/linux/ublk_cmd.h
> +++ b/include/uapi/linux/ublk_cmd.h
> @@ -51,6 +51,8 @@
>      _IOR('u', 0x13, struct ublksrv_ctrl_cmd)
>  #define UBLK_U_CMD_DEL_DEV_ASYNC    \
>      _IOR('u', 0x14, struct ublksrv_ctrl_cmd)
> +#define UBLK_U_CMD_UPDATE_SIZE        \
> +    _IOWR('u', 0x15, struct ublksrv_ctrl_cmd)
> 
>  /*
>   * 64bits are enough now, and it should be easy to extend in case of
> @@ -211,6 +213,11 @@
>   */
>  #define UBLK_F_USER_RECOVERY_FAIL_IO (1ULL << 9)
> 
> +/*
> + * Resizing a block device is possible with UBLK_U_CMD_UPDATE_SIZE
> + */
> +#define UBLK_F_UPDATE_SIZE         (1ULL << 10)

Please document how size is passed, and the unit is sector.

With above addressed, this patch looks fine.


Thanks,
Ming