[PATCH 06/13] libmultipath: Add cdev support
John Garry
john.g.garry at oracle.com
Wed Feb 25 07:32:18 PST 2026
Add support to create a cdev multipath device. The functionality is much
the same as NVMe, where the cdev is created when a mpath device is set
live.
The driver must provide a mpath_head_template.cdev_ioctl callback to
actually handle the ioctl.
Structure mpath_generic_chr_fops would be used for setting the cdev fops in
the mpath_head_template.add_cdev callback.
Signed-off-by: John Garry <john.g.garry at oracle.com>
---
include/linux/multipath.h | 15 +++++
lib/multipath.c | 116 ++++++++++++++++++++++++++++++++++++++
2 files changed, 131 insertions(+)
diff --git a/include/linux/multipath.h b/include/linux/multipath.h
index 4255b73de56b2..0dcfdd205237c 100644
--- a/include/linux/multipath.h
+++ b/include/linux/multipath.h
@@ -4,8 +4,11 @@
#include <linux/blkdev.h>
#include <linux/blk-mq.h>
+#include <linux/cdev.h>
#include <linux/srcu.h>
+#include <linux/io_uring/cmd.h>
+extern const struct file_operations mpath_generic_chr_fops;
extern const struct block_device_operations mpath_ops;
enum mpath_iopolicy_e {
@@ -45,9 +48,18 @@ struct mpath_device {
struct mpath_head_template {
bool (*available_path)(struct mpath_device *, bool *);
+ int (*add_cdev)(struct mpath_head *);
+ void (*del_cdev)(struct mpath_head *);
bool (*is_disabled)(struct mpath_device *);
bool (*is_optimized)(struct mpath_device *);
enum mpath_access_state (*get_access_state)(struct mpath_device *);
+ int (*cdev_ioctl)(struct mpath_head *, struct mpath_device *,
+ blk_mode_t mode, unsigned int cmd, unsigned long arg, int srcu_idx);
+ int (*chr_uring_cmd)(struct mpath_device *, struct io_uring_cmd *ioucmd,
+ unsigned int issue_flags);
+ int (*chr_uring_cmd_iopoll)(struct io_uring_cmd *ioucmd,
+ struct io_comp_batch *iob,
+ unsigned int poll_flags);
enum mpath_iopolicy_e (*get_iopolicy)(struct mpath_head *);
struct bio *(*clone_bio)(struct bio *);
const struct attribute_group **device_groups;
@@ -66,6 +78,9 @@ struct mpath_head {
spinlock_t requeue_lock;
struct work_struct requeue_work; /* work struct for requeue */
+ struct cdev cdev;
+ struct device cdev_device;
+
unsigned long flags;
struct mpath_device __rcu *current_path[MAX_NUMNODES];
const struct mpath_head_template *mpdt;
diff --git a/lib/multipath.c b/lib/multipath.c
index 7f3b0cccf053b..ce12d42918fdd 100644
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -469,6 +469,113 @@ const struct block_device_operations mpath_ops = {
};
EXPORT_SYMBOL_GPL(mpath_ops);
+static int mpath_generic_chr_open(struct inode *inode, struct file *file)
+{
+ struct cdev *cdev = file_inode(file)->i_cdev;
+ struct mpath_head *mpath_head =
+ container_of(cdev, struct mpath_head, cdev);
+
+ return mpath_get_head(mpath_head);
+}
+
+static int mpath_generic_chr_release(struct inode *inode, struct file *file)
+{
+ struct cdev *cdev = file_inode(file)->i_cdev;
+ struct mpath_head *mpath_head =
+ container_of(cdev, struct mpath_head, cdev);
+
+ mpath_put_head(mpath_head);
+ return 0;
+}
+
+static long mpath_generic_chr_ioctl(struct file *file, unsigned int cmd,
+ unsigned long arg)
+{
+ struct cdev *cdev = file_inode(file)->i_cdev;
+ struct mpath_head *mpath_head =
+ container_of(cdev, struct mpath_head, cdev);
+ struct mpath_device *mpath_device;
+ fmode_t mode = file->f_mode;
+ int srcu_idx, err = -EWOULDBLOCK;
+
+ srcu_idx = srcu_read_lock(&mpath_head->srcu);
+ mpath_device = mpath_find_path(mpath_head);
+ if (!mpath_device)
+ goto out_unlock;
+
+ /*
+ * If we are in the middle of error recovery, don't let anyone
+ * else try and use this device. Also, if error recovery fails, it
+ * may try and take the device offline, in which case all further
+ * access to the device is prohibited.
+ */
+ err = mpath_head->mpdt->cdev_ioctl(mpath_head, mpath_device,
+ mode, cmd, arg, srcu_idx);
+ lockdep_assert_not_held(&mpath_head->srcu);
+ return err;// ioctl must unlock
+
+out_unlock:
+ srcu_read_unlock(&mpath_head->srcu, srcu_idx);
+ return err;
+}
+
+static int mpath_generic_chr_uring_cmd(struct io_uring_cmd *ioucmd,
+ unsigned int issue_flags)
+{
+ struct cdev *cdev = file_inode(ioucmd->file)->i_cdev;
+ struct mpath_head *mpath_head =
+ container_of(cdev, struct mpath_head, cdev);
+ struct mpath_device *mpath_device;
+ int srcu_idx, ret = -EWOULDBLOCK;
+
+ if (!mpath_head->mpdt->chr_uring_cmd)
+ return -EOPNOTSUPP;
+
+ srcu_idx = srcu_read_lock(&mpath_head->srcu);
+ mpath_device = mpath_find_path(mpath_head);
+
+ if (!mpath_device)
+ goto out_unlock;
+
+ ret = mpath_head->mpdt->chr_uring_cmd(mpath_device, ioucmd,
+ issue_flags);
+out_unlock:
+ srcu_read_unlock(&mpath_head->srcu, srcu_idx);
+ return ret;
+}
+
+static int mpath_generic_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd,
+ struct io_comp_batch *iob,
+ unsigned int poll_flags)
+{
+ struct cdev *cdev = file_inode(ioucmd->file)->i_cdev;
+ struct mpath_head *mpath_head =
+ container_of(cdev, struct mpath_head, cdev);
+
+ if (!mpath_head->mpdt->chr_uring_cmd_iopoll)
+ return -EOPNOTSUPP;
+
+ return mpath_head->mpdt->chr_uring_cmd_iopoll(ioucmd, iob, poll_flags);
+}
+
+const struct file_operations mpath_generic_chr_fops = {
+ .owner = THIS_MODULE,
+ .open = mpath_generic_chr_open,
+ .release = mpath_generic_chr_release,
+ .unlocked_ioctl = mpath_generic_chr_ioctl,
+ .compat_ioctl = compat_ptr_ioctl,
+ .uring_cmd = mpath_generic_chr_uring_cmd,
+ .uring_cmd_iopoll = mpath_generic_chr_uring_cmd_iopoll,
+};
+EXPORT_SYMBOL_GPL(mpath_generic_chr_fops);
+
+static int mpath_head_add_cdev(struct mpath_head *mpath_head)
+{
+ if (mpath_head->mpdt->add_cdev)
+ return mpath_head->mpdt->add_cdev(mpath_head);
+ return 0;
+}
+
static void multipath_partition_scan_work(struct work_struct *work)
{
struct mpath_disk *mpath_disk =
@@ -501,6 +608,12 @@ void mpath_requeue_work(struct work_struct *work)
}
EXPORT_SYMBOL_GPL(mpath_requeue_work);
+static void mpath_head_del_cdev(struct mpath_head *mpath_head)
+{
+ if (mpath_head->mpdt->del_cdev)
+ mpath_head->mpdt->del_cdev(mpath_head);
+}
+
void mpath_remove_disk(struct mpath_disk *mpath_disk)
{
struct mpath_head *mpath_head = mpath_disk->mpath_head;
@@ -514,6 +627,7 @@ void mpath_remove_disk(struct mpath_disk *mpath_disk)
*/
kblockd_schedule_work(&mpath_head->requeue_work);
+ mpath_head_del_cdev(mpath_head);
mpath_synchronize(mpath_head);
del_gendisk(disk);
}
@@ -572,6 +686,8 @@ void mpath_device_set_live(struct mpath_disk *mpath_disk,
clear_bit(MPATH_HEAD_DISK_LIVE, &mpath_head->flags);
return;
}
+
+ mpath_head_add_cdev(mpath_head);
queue_work(mpath_wq, &mpath_disk->partition_scan_work);
}
--
2.43.5
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