On 02/03/2026 12:31, Nilay Shroff wrote:
+#define MPATH_HEAD_DISK_LIVE 0
+
struct mpath_head {
struct srcu_struct srcu;
struct list_head dev_list; /* list of all mpath_devs */
@@ -17,12 +34,36 @@ struct mpath_head {
struct kref ref;
+ unsigned long flags;
struct mpath_device __rcu *current_path[MAX_NUMNODES];
+ const struct mpath_head_template *mpdt;
void *drvdata;
};
Not sure why we don't have back reference to struct mpath_disk
from struct mpath_head here. Does it make sense to have this?
We can get away without it.
Some more background info .. so the concept of separate mpath_head and
mpath_disk is driven by SCSI, which has scsi_device and scsi_disk
classes. The scsi_disk driver (sd.c) controls the per-path gendisk and
the mpath_disk, and these internals are hidden from the scsi_core (which
controls the scsi_device). SCSI having this layered approach makes
things more complicated. This is unlike NVMe, where the core driver
controls the NS gendisk also.
+static inline struct mpath_disk *mpath_bd_device_to_disk(struct
device *dev)
+{
+ return dev_get_drvdata(dev);
+}
+
+static inline struct mpath_disk *mpath_gendisk_to_disk(struct gendisk
*disk)
+{
+ return mpath_bd_device_to_disk(disk_to_dev(disk));
+}
+
int mpath_get_head(struct mpath_head *mpath_head);
void mpath_put_head(struct mpath_head *mpath_head);
struct mpath_head *mpath_alloc_head(void);
+void mpath_put_disk(struct mpath_disk *mpath_disk);
+void mpath_remove_disk(struct mpath_disk *mpath_disk);
+void mpath_unregister_disk(struct mpath_disk *mpath_disk);
+struct mpath_disk *mpath_alloc_head_disk(struct queue_limits *lim,
+ int numa_node);
+void mpath_device_set_live(struct mpath_disk *mpath_disk,
+ struct mpath_device *mpath_device);
+void mpath_unregister_disk(struct mpath_disk *mpath_disk);
+static inline bool is_mpath_head(struct gendisk *disk)
+{
+ return disk->fops == &mpath_ops;
+}
#endif // _LIBMULTIPATH_H
diff --git a/lib/multipath.c b/lib/multipath.c
index 15c495675d729..88efb0ae16acb 100644
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -32,6 +32,135 @@ void mpath_put_head(struct mpath_head *mpath_head)
}
EXPORT_SYMBOL_GPL(mpath_put_head);
+static void mpath_free_disk(struct kref *ref)
+{
+ struct mpath_disk *mpath_disk =
+ container_of(ref, struct mpath_disk, ref);
+ struct mpath_head *mpath_head = mpath_disk->mpath_head;
+
+ put_disk(mpath_disk->disk);
+ mpath_put_head(mpath_head);
+ kfree(mpath_disk);
+}
+
The mpath_alloc_head_disk() doesn't get a reference to the
mpath_head object but here while freeing mpath_disk we put
the reference to mpath_head. Would that create a reference
imbalance?
I think that what I done can be improved. If you check
nvme_mpath_alloc_disk(), when we alloc the head the ref is 1, and then
we rely on the disk release to release that head reference.
Yes we got a reference to mpath_head while
allocating it but then these are two (alloc mpath_disk and
alloc mpath_head) disjoint operations. In that case, can't
we have both mpath_disk and mpath_head allocated under one
libmultipath API?
I would like to have something simpler (like mainline NVMe code), but I
have it this way because of SCSI, as above.
Thanks
