dm: add support for get_unique_id

This adds support to obtain a device's unique id through dm, similar to the
existing ioctl and persistent resevation handling.  We limit this to
single-target devices.

This enables knfsd to export pNFS SCSI luns that have been exported from
multipath devices.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index adf0dde689475e0e674acac036058b435474a917..12ecf07a38410a37afff76037b25c6a17c605c69 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -3343,6 +3343,59 @@ void dm_free_md_mempools(struct dm_md_mempools *pools)
        kfree(pools);
 }
 
+struct dm_blkdev_id {
+       u8 *id;
+       enum blk_unique_id type;
+};
+
+static int __dm_get_unique_id(struct dm_target *ti, struct dm_dev *dev,
+                               sector_t start, sector_t len, void *data)
+{
+       struct dm_blkdev_id *dm_id = data;
+       const struct block_device_operations *fops = dev->bdev->bd_disk->fops;
+
+       if (!fops->get_unique_id)
+               return 0;
+
+       return fops->get_unique_id(dev->bdev->bd_disk, dm_id->id, dm_id->type);
+}
+
+/*
+ * Allow access to get_unique_id() for the first device returning a
+ * non-zero result.  Reasonable use expects all devices to have the
+ * same unique id.
+ */
+static int dm_blk_get_unique_id(struct gendisk *disk, u8 *id,
+               enum blk_unique_id type)
+{
+       struct mapped_device *md = disk->private_data;
+       struct dm_table *table;
+       struct dm_target *ti;
+       int ret = 0, srcu_idx;
+
+       struct dm_blkdev_id dm_id = {
+               .id = id,
+               .type = type,
+       };
+
+       table = dm_get_live_table(md, &srcu_idx);
+       if (!table || !dm_table_get_size(table))
+               goto out;
+
+       /* We only support devices that have a single target */
+       if (table->num_targets != 1)
+               goto out;
+       ti = dm_table_get_target(table, 0);
+
+       if (!ti->type->iterate_devices)
+               goto out;
+
+       ret = ti->type->iterate_devices(ti, __dm_get_unique_id, &dm_id);
+out:
+       dm_put_live_table(md, srcu_idx);
+       return ret;
+}
+
 struct dm_pr {
        u64     old_key;
        u64     new_key;
@@ -3668,6 +3721,7 @@ static const struct block_device_operations dm_blk_dops = {
        .ioctl = dm_blk_ioctl,
        .getgeo = dm_blk_getgeo,
        .report_zones = dm_blk_report_zones,
+       .get_unique_id = dm_blk_get_unique_id,
        .pr_ops = &dm_pr_ops,
        .owner = THIS_MODULE
 };
@@ -3677,6 +3731,7 @@ static const struct block_device_operations dm_rq_blk_dops = {
        .release = dm_blk_close,
        .ioctl = dm_blk_ioctl,
        .getgeo = dm_blk_getgeo,
+       .get_unique_id = dm_blk_get_unique_id,
        .pr_ops = &dm_pr_ops,
        .owner = THIS_MODULE
 };