On Wed, Feb 25, 2026 at 03:36:24PM +0000, John Garry wrote:
> Add support to attach a multipath disk.
>
> We still allocate the gendisk per path, and this is required for the
> per-path submission. However, those gendisks are marked as hidden. Those
> disks are named sdX:Y, where X is the multipath disk index and Y is the
> per-path index.
>
> A global list of sd_mpath_disks is kept for matching scsi_device's.
>
> The multipath gendisk has the name and disk->major/minor set to minic a
> scsi_disk.
>
> The following is an example of relevant scsi_disk and block sysfs
> directories:
>
> $ ls -l /sys/block/ | grep sdc
> lrwxrwxrwx 1 root root 0 Feb 24 16:01 sdc ->
> ../devices/virtual/scsi_mpath_disk/0/sdc
> lrwxrwxrwx 1 root root 0 Feb 24 16:01 sdc:0 ->
> ../devices/platform/host8/session1/target8:0:0/8:0:0:0/block/sdc:0
> lrwxrwxrwx 1 root root 0 Feb 24 16:02 sdc:1 ->
> ../devices/platform/host9/session2/target9:0:0/9:0:0:0/block/sdc:1
>
> $ ls -l /sys/class/scsi_mpath_disk/0/
> total 0
> drwxr-xr-x 2 root root 0 Feb 24 16:03 power
> drwxr-xr-x 11 root root 0 Feb 24 16:01 sdc
> lrwxrwxrwx 1 root root 0 Feb 24 16:01 subsystem ->
> ../../../../class/scsi_mpath_disk
> -rw-r--r-- 1 root root 4096 Feb 24 16:01 uevent
>
> $ ls -l /sys/class/scsi_mpath_disk/0/sdc/multipath/
> total 0
> lrwxrwxrwx 1 root root 0 Feb 24 16:20 sdc:0 ->
> ../../../../../platform/host8/session1/target8:0:0/8:0:0:0/block/sdc:0
> lrwxrwxrwx 1 root root 0 Feb 24 16:20 sdc:1 ->
> ../../../../../platform/host9/session2/target9:0:0/9:0:0:0/block/sdc:1
>
>
> $ ls -l /dev/sdc*
> brw-rw---- 1 root disk 8, 32 Feb 24 16:01 /dev/sdc
> brw-rw---- 1 root disk 8, 33 Feb 24 16:01 /dev/sdc1
> brw-rw---- 1 root disk 8, 34 Feb 24 16:01 /dev/sdc2
>
>
> $ lsblk /dev/sdc
> NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
> sdc 8:32 0 600M 0 disk
> |-sdc1 8:33 0 9M 0 part
> `-sdc2 8:34 0 568M 0 part
>
> Signed-off-by: John Garry <[email protected]>
> ---
> drivers/scsi/sd.c | 376 +++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 358 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 9617878b53ec6..409c0937764d9 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -117,12 +117,33 @@ static DEFINE_IDA(sd_index_ida);
> static mempool_t *sd_page_pool;
> static struct lock_class_key sd_bio_compl_lkclass;
> #ifdef CONFIG_SCSI_MULTIPATH
> +static LIST_HEAD(sd_mpath_disks_list);
> +static DEFINE_MUTEX(sd_mpath_disks_lock);
> +
> struct sd_mpath_disk {
> + struct device dev;
> + int disk_index;
> + int disk_count;
> + struct list_head entry;
> + struct mutex lock;
> struct mpath_disk *mpath_disk;
> + struct scsi_mpath_head *scsi_mpath_head;
> };
>
> static void sd_mpath_disk_release(struct device *dev)
> {
> + struct sd_mpath_disk *sd_mpath_disk =
> + container_of(dev, struct sd_mpath_disk, dev);
> + struct scsi_mpath_head *scsi_mpath_head =
> + sd_mpath_disk->scsi_mpath_head;
> + struct mpath_disk *mpath_disk = sd_mpath_disk->mpath_disk;
> +
> + mpath_put_disk(mpath_disk);
> +
> + ida_free(&sd_index_ida, sd_mpath_disk->disk_index);
> + scsi_mpath_put_head(scsi_mpath_head);
> +
> + kfree(sd_mpath_disk);
> }
>
> static const struct class sd_mpath_disk_class = {
> @@ -4144,7 +4165,302 @@ static const struct scsi_mpath_pr_ops sd_mpath_pr_ops
> = {
> .pr_read_keys = sd_mpath_pr_read_keys,
> .pr_read_reservation = sd_mpath_pr_read_reservation,
> };
> +
> +static int sd_mpath_revalidate_head(struct scsi_disk *sdkp)
> +{
> + struct sd_mpath_disk *sd_mpath_disk = sdkp->sd_mpath_disk;
> + struct mpath_disk *mpath_disk = sd_mpath_disk->mpath_disk;;
> + struct gendisk *disk = mpath_disk->disk;
> + struct queue_limits *sdkp_lim = &sdkp->disk->queue->limits;
> + struct queue_limits lim;
> + unsigned int memflags;
> + int ret;
> +
> + lim = queue_limits_start_update(disk->queue);
> + memflags = blk_mq_freeze_queue(disk->queue);
> +
> + lim.logical_block_size = sdkp_lim->logical_block_size;
> + lim.physical_block_size = sdkp_lim->physical_block_size;
> + lim.io_min = sdkp_lim->io_min;
> + lim.io_opt = sdkp_lim->io_opt;
> +
> + queue_limits_stack_bdev(&lim, sdkp->disk->part0, 0,
> + disk->disk_name);
> +
> + /* TODO: setup integrity limits */
> + lim.max_write_streams = sdkp_lim->max_write_streams;
> + lim.write_stream_granularity = sdkp_lim->write_stream_granularity;
> + ret = queue_limits_commit_update(disk->queue, &lim);
> +
> + set_capacity_and_notify(disk, get_capacity(sdkp->disk));
> +
> + blk_mq_unfreeze_queue(disk->queue, memflags);
> +
> + return ret;
> +}
> +static int sd_mpath_get_disk(struct sd_mpath_disk *sd_mpath_disk)
> +{
> + if (!get_device(&sd_mpath_disk->dev))
> + return -ENXIO;
> + return 0;
> +}
> +
> +static void sd_mpath_put_disk(struct sd_mpath_disk *sd_mpath_disk)
> +{
> + put_device(&sd_mpath_disk->dev);
> +}
> +
> +static struct sd_mpath_disk *sd_mpath_find_disk(struct scsi_device *sdp)
> +{
> + struct scsi_mpath_device *scsi_mpath_dev = sdp->scsi_mpath_dev;
> + struct sd_mpath_disk *sd_mpath_disk;
> + int ret;
> +
> + mutex_lock(&sd_mpath_disks_lock);
> + list_for_each_entry(sd_mpath_disk, &sd_mpath_disks_list, entry) {
> + struct scsi_mpath_head *scsi_mpath_head;
> + struct mpath_disk *mpath_disk;
> + struct mpath_head *mpath_head;
> +
> + ret = sd_mpath_get_disk(sd_mpath_disk);
> + if (ret)
> + continue;
> + mpath_disk = sd_mpath_disk->mpath_disk;
> + mpath_head = mpath_disk->mpath_head;
> + scsi_mpath_head = mpath_head->drvdata;
> +
> + if (strncmp(scsi_mpath_head->wwid,
> + scsi_mpath_dev->device_id_str,
> + SCSI_MPATH_DEVICE_ID_LEN) == 0) {
> +
> + mutex_unlock(&sd_mpath_disks_lock);
> + return sd_mpath_disk;
> + }
> + sd_mpath_put_disk(sd_mpath_disk);
> + }
> +
> + return NULL;
> +}
> +
> +static void sd_mpath_add_disk(struct scsi_disk *sdkp)
> +{
> + struct scsi_device *sdp = sdkp->device;
> + struct scsi_mpath_device *scsi_mpath_dev = sdp->scsi_mpath_dev;
> + struct mpath_device *mpath_device = &scsi_mpath_dev->mpath_device;
> + struct sd_mpath_disk *sd_mpath_disk = sdkp->sd_mpath_disk;
> + struct mpath_disk *mpath_disk = sd_mpath_disk->mpath_disk;
> + struct mpath_head *mpath_head = mpath_disk->mpath_head;
> +
> + mpath_device->disk = sdkp->disk;
> + mpath_add_device(mpath_head, mpath_device);
> + mpath_device_set_live(mpath_disk, mpath_device);
> +}
> +
> +static int sd_mpath_probe(struct scsi_disk *sdkp)
> +{
> + struct scsi_device *sdp = sdkp->device;
> + struct scsi_mpath_device *scsi_mpath_dev = sdp->scsi_mpath_dev;
> + struct device *dma_dev = sdp->host->dma_dev;
> + struct scsi_mpath_head *scsi_mpath_head =
> + scsi_mpath_dev->scsi_mpath_head;
> + struct sd_mpath_disk *sd_mpath_disk;
> + struct mpath_head *mpath_head = scsi_mpath_head->mpath_head;
> + struct queue_limits lim;
> + struct gendisk *disk;
> + int error;
> +
> + /*
> + * sd_mpath_disks_list is kept locked if no disk found.
> + * Otherwise an extra reference is taken.
> + */
Again, I personally think the logic is easier to follow when all the
locking isn't split over multiple functions.
> + sd_mpath_disk = sd_mpath_find_disk(sdp);
> + if (sd_mpath_disk) {
> + mutex_lock(&sd_mpath_disk->lock);
> + sd_mpath_disk->disk_count++;
> + mutex_unlock(&sd_mpath_disk->lock);
> + goto found;
> + }
> +
> + sd_mpath_disk = kzalloc(sizeof(*sd_mpath_disk), GFP_KERNEL);
> + if (!sd_mpath_disk) {
> + error = -ENOMEM;
> + goto out_unlock;
> + }
> +
> + sd_mpath_disk->scsi_mpath_head = scsi_mpath_head;
> + device_initialize(&sd_mpath_disk->dev);
> + mutex_init(&sd_mpath_disk->lock);
> + sd_mpath_disk->dev.class = &sd_mpath_disk_class;
> +
> + blk_set_stacking_limits(&lim);
> + lim.dma_alignment = 3;
> + lim.features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT |
> + BLK_FEAT_POLL | BLK_FEAT_ATOMIC_WRITES;
> +
> + sd_mpath_disk->mpath_disk = mpath_alloc_head_disk(&lim,
> + dev_to_node(dma_dev));
> + if (!sd_mpath_disk->mpath_disk) {
> + error = -ENOMEM;
> + goto out_free_disk;
> + }
> + disk = sd_mpath_disk->mpath_disk->disk;
> + mpath_get_head(mpath_head); /* undone in mpath_free_disk() */
> +
> + sd_mpath_disk->mpath_disk->mpath_head = mpath_head;
> + sd_mpath_disk->mpath_disk->parent = &sd_mpath_disk->dev;
> +
> + error = ida_alloc(&sd_index_ida, GFP_KERNEL);
> + if (error < 0) {
> + sdev_printk(KERN_WARNING, sdp, "sd_probe: memory exhausted.\n");
> + goto out_put_disk;
> + }
> + sd_mpath_disk->disk_index = error;
> + error = sd_format_disk_name("sd", sd_mpath_disk->disk_index,
> + disk->disk_name, DISK_NAME_LEN);
> + if (error)
> + goto out_free_index;
> +
> + error = dev_set_name(&sd_mpath_disk->dev, "%s",
> + dev_name(&scsi_mpath_head->dev));
> + if (error)
> + goto out_free_index;
> +
> + /* undone in sd_mpath_disk_release() */
> + scsi_mpath_get_head(scsi_mpath_head);
> +
> + error = device_add(&sd_mpath_disk->dev);
> + if (error) {
> + put_device(&sd_mpath_disk->dev);
> + goto out_unlock;
We should clean up when we fail here, instead of just unlocking without
fully setting things up.
-Ben
> + }
> +
> + list_add_tail(&sd_mpath_disk->entry, &sd_mpath_disks_list);
> + disk->major = sd_major((sd_mpath_disk->disk_index & 0xf0) >> 4);
> + disk->first_minor = ((sd_mpath_disk->disk_index & 0xf) << 4) |
> + (sd_mpath_disk->disk_index & 0xfff00);
> + disk->minors = SD_MINORS;
> +
> + sd_mpath_disk->disk_count = 1;
> + mutex_unlock(&sd_mpath_disks_lock);
> +
> +found:
> + sdkp->sd_mpath_disk = sd_mpath_disk;
> + sdkp->disk->flags |= GENHD_FL_HIDDEN;
> + snprintf(sdkp->disk->disk_name, DISK_NAME_LEN, "%s:%d",
> + sd_mpath_disk->mpath_disk->disk->disk_name,
> + scsi_mpath_dev->index);
> +
> + sdkp->index = -1;
> + return 0;
> +
> +out_free_index:
> + ida_free(&sd_index_ida, sd_mpath_disk->disk_index);
> +out_put_disk:
> + mpath_put_disk(sd_mpath_disk->mpath_disk);
> +out_free_disk:
> + kfree(sd_mpath_disk);
> +out_unlock:
> + mutex_unlock(&sd_mpath_disks_lock);
> + return error;
> +}
