ublk: add UBLK_CMD_TRY_STOP_DEV command

Add a best-effort stop command, UBLK_CMD_TRY_STOP_DEV, which only stops a
ublk device when it has no active openers.

Unlike UBLK_CMD_STOP_DEV, this command does not disrupt existing users.
New opens are blocked only after disk_openers has reached zero; if the
device is busy, the command returns -EBUSY and leaves it running.

The ub->block_open flag is used only to close a race with an in-progress
open and does not otherwise change open behavior.

Advertise support via the UBLK_F_SAFE_STOP_DEV feature flag.

Signed-off-by: Yoav Cohen <yoav@nvidia.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 73490890242b86924ccb447921034402a02ea6b9..aaf94d2fb78971663b54eb74c100b94c0d417590 100644 (file)
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -56,6 +56,7 @@
 #define UBLK_CMD_DEL_DEV_ASYNC _IOC_NR(UBLK_U_CMD_DEL_DEV_ASYNC)
 #define UBLK_CMD_UPDATE_SIZE   _IOC_NR(UBLK_U_CMD_UPDATE_SIZE)
 #define UBLK_CMD_QUIESCE_DEV   _IOC_NR(UBLK_U_CMD_QUIESCE_DEV)
+#define UBLK_CMD_TRY_STOP_DEV  _IOC_NR(UBLK_U_CMD_TRY_STOP_DEV)
 
 #define UBLK_IO_REGISTER_IO_BUF                _IOC_NR(UBLK_U_IO_REGISTER_IO_BUF)
 #define UBLK_IO_UNREGISTER_IO_BUF      _IOC_NR(UBLK_U_IO_UNREGISTER_IO_BUF)
@@ -76,7 +77,8 @@
                | UBLK_F_QUIESCE \
                | UBLK_F_PER_IO_DAEMON \
                | UBLK_F_BUF_REG_OFF_DAEMON \
-               | (IS_ENABLED(CONFIG_BLK_DEV_INTEGRITY) ? UBLK_F_INTEGRITY : 0))
+               | (IS_ENABLED(CONFIG_BLK_DEV_INTEGRITY) ? UBLK_F_INTEGRITY : 0) \
+               | UBLK_F_SAFE_STOP_DEV)
 
 #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
                | UBLK_F_USER_RECOVERY_REISSUE \
@@ -243,6 +245,8 @@ struct ublk_device {
        struct delayed_work     exit_work;
        struct work_struct      partition_scan_work;
 
+       bool                    block_open; /* protected by open_mutex */
+
        struct ublk_queue       *queues[];
 };
 
@@ -984,6 +988,9 @@ static int ublk_open(struct gendisk *disk, blk_mode_t mode)
                        return -EPERM;
        }
 
+       if (ub->block_open)
+               return -ENXIO;
+
        return 0;
 }
 
@@ -3343,7 +3350,8 @@ static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_cmd *header)
        ub->dev_info.flags |= UBLK_F_CMD_IOCTL_ENCODE |
                UBLK_F_URING_CMD_COMP_IN_TASK |
                UBLK_F_PER_IO_DAEMON |
-               UBLK_F_BUF_REG_OFF_DAEMON;
+               UBLK_F_BUF_REG_OFF_DAEMON |
+               UBLK_F_SAFE_STOP_DEV;
 
        /* GET_DATA isn't needed any more with USER_COPY or ZERO COPY */
        if (ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY |
@@ -3464,6 +3472,34 @@ static void ublk_ctrl_stop_dev(struct ublk_device *ub)
        ublk_stop_dev(ub);
 }
 
+static int ublk_ctrl_try_stop_dev(struct ublk_device *ub)
+{
+       struct gendisk *disk;
+       int ret = 0;
+
+       disk = ublk_get_disk(ub);
+       if (!disk)
+               return -ENODEV;
+
+       mutex_lock(&disk->open_mutex);
+       if (disk_openers(disk) > 0) {
+               ret = -EBUSY;
+               goto unlock;
+       }
+       ub->block_open = true;
+       /* release open_mutex as del_gendisk() will reacquire it */
+       mutex_unlock(&disk->open_mutex);
+
+       ublk_ctrl_stop_dev(ub);
+       goto out;
+
+unlock:
+       mutex_unlock(&disk->open_mutex);
+out:
+       ublk_put_disk(disk);
+       return ret;
+}
+
 static int ublk_ctrl_get_dev_info(struct ublk_device *ub,
                const struct ublksrv_ctrl_cmd *header)
 {
@@ -3859,6 +3895,7 @@ static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
        case UBLK_CMD_END_USER_RECOVERY:
        case UBLK_CMD_UPDATE_SIZE:
        case UBLK_CMD_QUIESCE_DEV:
+       case UBLK_CMD_TRY_STOP_DEV:
                mask = MAY_READ | MAY_WRITE;
                break;
        default:
@@ -3972,6 +4009,9 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
        case UBLK_CMD_QUIESCE_DEV:
                ret = ublk_ctrl_quiesce_dev(ub, header);
                break;
+       case UBLK_CMD_TRY_STOP_DEV:
+               ret = ublk_ctrl_try_stop_dev(ub);
+               break;
        default:
                ret = -EOPNOTSUPP;
                break;

diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 61ac5d8e1078804800753b01ac4211d5d031bfe6..90f47da4f435f0e06dbbd769d9405c327241c560 100644 (file)
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -55,7 +55,8 @@
        _IOWR('u', 0x15, struct ublksrv_ctrl_cmd)
 #define UBLK_U_CMD_QUIESCE_DEV         \
        _IOWR('u', 0x16, struct ublksrv_ctrl_cmd)
-
+#define UBLK_U_CMD_TRY_STOP_DEV                \
+       _IOWR('u', 0x17, struct ublksrv_ctrl_cmd)
 /*
  * 64bits are enough now, and it should be easy to extend in case of
  * running out of feature flags
@@ -321,6 +322,12 @@
  */
 #define UBLK_F_INTEGRITY (1ULL << 16)
 
+/*
+ * The device supports the UBLK_CMD_TRY_STOP_DEV command, which
+ * allows stopping the device only if there are no openers.
+ */
+#define UBLK_F_SAFE_STOP_DEV   (1ULL << 17)
+
 /* device state */
 #define UBLK_S_DEV_DEAD        0
 #define UBLK_S_DEV_LIVE        1