ublk_drv: add device parameter UBLK_PARAM_TYPE_DEVT

Userspace side only knows device ID, but the associated path of ublkc* and
ublkb* could be changed by udev, and that depends on userspace's policy, so
add parameter of UBLK_PARAM_TYPE_DEVT for retrieving major/minor of the
ublkc* and ublkb*, then user may figure out major/minor of the ublk disks
he/she owns. With major/minor, it is easy to find the device node path.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230106041711.914434-5-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 b015e46b59bbcee700a7a9afc8373f4ec784efad..75033304b90010cb698a18e52b23a82ca7634feb 100644 (file)
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -54,7 +54,8 @@
                | UBLK_F_USER_RECOVERY_REISSUE)
 
 /* All UBLK_PARAM_TYPE_* should be included here */
-#define UBLK_PARAM_TYPE_ALL (UBLK_PARAM_TYPE_BASIC | UBLK_PARAM_TYPE_DISCARD)
+#define UBLK_PARAM_TYPE_ALL (UBLK_PARAM_TYPE_BASIC | \
+               UBLK_PARAM_TYPE_DISCARD | UBLK_PARAM_TYPE_DEVT)
 
 struct ublk_rq_data {
        struct llist_node node;
@@ -255,6 +256,10 @@ static int ublk_validate_params(const struct ublk_device *ub)
                        return -EINVAL;
        }
 
+       /* dev_t is read-only */
+       if (ub->params.types & UBLK_PARAM_TYPE_DEVT)
+               return -EINVAL;
+
        return 0;
 }
 
@@ -1777,6 +1782,22 @@ static int ublk_ctrl_get_dev_info(struct ublk_device *ub,
        return 0;
 }
 
+/* TYPE_DEVT is readonly, so fill it up before returning to userspace */
+static void ublk_ctrl_fill_params_devt(struct ublk_device *ub)
+{
+       ub->params.devt.char_major = MAJOR(ub->cdev_dev.devt);
+       ub->params.devt.char_minor = MINOR(ub->cdev_dev.devt);
+
+       if (ub->ub_disk) {
+               ub->params.devt.disk_major = MAJOR(disk_devt(ub->ub_disk));
+               ub->params.devt.disk_minor = MINOR(disk_devt(ub->ub_disk));
+       } else {
+               ub->params.devt.disk_major = 0;
+               ub->params.devt.disk_minor = 0;
+       }
+       ub->params.types |= UBLK_PARAM_TYPE_DEVT;
+}
+
 static int ublk_ctrl_get_params(struct ublk_device *ub,
                struct io_uring_cmd *cmd)
 {
@@ -1798,6 +1819,7 @@ static int ublk_ctrl_get_params(struct ublk_device *ub,
                ph.len = sizeof(struct ublk_params);
 
        mutex_lock(&ub->mutex);
+       ublk_ctrl_fill_params_devt(ub);
        if (copy_to_user(argp, &ub->params, ph.len))
                ret = -EFAULT;
        else

diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 8f88e3a29998fb6e79672e3122caa88d11331945..4e38b9aa02933f517b3f02fe0a9e4fbe966f2a69 100644 (file)
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -214,6 +214,17 @@ struct ublk_param_discard {
        __u16   reserved0;
 };
 
+/*
+ * read-only, can't set via UBLK_CMD_SET_PARAMS, disk_devt is available
+ * after device is started
+ */
+struct ublk_param_devt {
+       __u32   char_major;
+       __u32   char_minor;
+       __u32   disk_major;
+       __u32   disk_minor;
+};
+
 struct ublk_params {
        /*
         * Total length of parameters, userspace has to set 'len' for both
@@ -224,10 +235,12 @@ struct ublk_params {
        __u32   len;
 #define UBLK_PARAM_TYPE_BASIC           (1 << 0)
 #define UBLK_PARAM_TYPE_DISCARD         (1 << 1)
+#define UBLK_PARAM_TYPE_DEVT            (1 << 2)
        __u32   types;                  /* types of parameter included */
 
        struct ublk_param_basic         basic;
        struct ublk_param_discard       discard;
+       struct ublk_param_devt          devt;
 };
 
 #endif