[PATCH v4]: 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      | 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)
      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):
          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):
+        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)
+
  /* device state */
  #define UBLK_S_DEV_DEAD    0
  #define UBLK_S_DEV_LIVE    1
-- 
2.43.0