[PATCH v2] ublk: Add UBLK_U_CMD_UPDATE_SIZE

[Jared Holzman <jholzman@nvidia.com>]

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      | 23 ++++++++++++++++++++++-
  include/uapi/linux/ublk_cmd.h |  7 +++++++
  2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 2fd05c1bd30b..acf8aa6c4452 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 \
@@ -3052,6 +3053,22 @@ static int ublk_ctrl_get_features(struct 
io_uring_cmd *cmd)
         return 0;
  }

+static int ublk_ctrl_set_size(struct ublk_device *ub,
+               struct io_uring_cmd *cmd)
+{
+       const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+       struct ublk_param_basic *p = &ub->params.basic;
+       size_t new_size = (int)header->data[0];
+       int ret = 0;
+
+       p->dev_sectors = new_size;
+
+       mutex_lock(&ub->mutex);
+       set_capacity_and_notify(ub->ub_disk, p->dev_sectors);
+       mutex_unlock(&ub->mutex);
+
+       return ret;
+}

  /*
   * All control commands are sent via /dev/ublk-control, so we have to 
check
   * the destination device's permission
@@ -3137,6 +3154,7 @@ 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):
                 mask = MAY_READ | MAY_WRITE;
                 break;
         default:
@@ -3228,6 +3246,9 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd 
*cmd,
         case UBLK_CMD_END_USER_RECOVERY:
                 ret = ublk_ctrl_end_recovery(ub, cmd);
                 break;
+       case _IOC_NR(UBLK_U_CMD_UPDATE_SIZE):
+               ret = ublk_ctrl_set_size(ub, cmd);
+               break;
         default:
                 ret = -EOPNOTSUPP;
                 break;
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 583b86681c93..0e40e497c28f 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)

+/*
+ * Resisizing a block device is possible with UBLK_U_CMD_UPDATE_SIZE
+ */
+#define UBLK_F_UPDATE_SIZE              (1ULL << 10)
+
  /* device state */
  #define UBLK_S_DEV_DEAD        0
  #define UBLK_S_DEV_LIVE        1
-- 
2.43.0