[PATCH v8 00/27] Native SCSI Multipath support
John Garry
john.garry at linux.dev
Wed Sep 23 10:16:17 PDT 2026
On 9/7/26 11:49, John Garry wrote:
> NATIVE SCSI MULTIPATH:
>
JFYI, this passes a sanity test on mkp scsi 7.4 queue after all the
recent sense codes changes, as would be expected.
> This series introduces native SCSI multipath support. It is intended as
> an alternative to dm-mpath.
>
> This support aims to provide a multipath-enabled SCSI block device/
> gendisk.
>
> For a SCSI device to support native multipath, either of the following
> conditions must be satisfied:
> a. unique ID in VPD page 83 and ALUA support and scsi_multipath modparam
> enabled
> b. unique ID in VPD page 83 and scsi_multipath_always modparam enabled
>
> This series relies on reading sdev->access_state to get path information.
> This path information would be provided by ALUA. ALUA support which does
> not rely on device handlers has already been discussed at
> https://lore.kernel.org/linux-scsi/7755e98f-5619-48ba-bcfc-b64eec930c40@oracle.com/
> and support will be added in the next phase.
>
> New classes of devices are added:
> - scsi_mpath_device
> - scsi_mpath_disk
>
> These are required since a multipath scsi_device has no common scsi host.
> An example of the sysfs files and directories for these new classes is as
> follows:
>
> $ ls -l /sys/class/scsi_mpath_device/scsi_mpath_device0/
> total 0
> -rw-r--r-- 1 root root 4096 Feb 25 11:59 iopolicy
> drwxr-xr-x 2 root root 0 Feb 25 11:59 multipath
> drwxr-xr-x 2 root root 0 Feb 25 11:59 power
> lrwxrwxrwx 1 root root 0 Feb 25 11:59 subsystem ->
> ../../../../class/scsi_mpath_device
> -rw-r--r-- 1 root root 4096 Feb 25 11:58 uevent
> -r--r--r-- 1 root root 4096 Feb 25 11:59 vpd_id
> $ ls -l /sys/class/scsi_mpath_device/scsi_mpath_device0/multipath/
> total 0
> lrwxrwxrwx 1 root root 0 Feb 25 11:59 8:0:0:0 ->
> ../../../../platform/host8/session1/target8:0:0/8:0:0:0
> lrwxrwxrwx 1 root root 0 Feb 25 11:59 9:0:0:0 ->
> ../../../../platform/host9/session2/target9:0:0/9:0:0:0
> $ cat /sys/class/scsi_mpath_device/scsi_mpath_device0/vpd_id
> naa.600140505200a986f0043c9afa1fd077
> $ cat /sys/class/scsi_mpath_device/scsi_mpath_device0/iopolicy
> numa
> $
>
> $ ls -l /sys/class/scsi_mpath_disk/scsi_mpath_disk0/
> total 0
> drwxr-xr-x 2 root root 0 Feb 25 12:00 power
> drwxr-xr-x 11 root root 0 Feb 25 11:58 sdc
> lrwxrwxrwx 1 root root 0 Feb 25 11:58 subsystem ->
> ../../../../class/scsi_mpath_disk
> -rw-r--r-- 1 root root 4096 Feb 25 11:58 uevent
> $ ls -l /sys/class/scsi_mpath_disk/scsi_mpath_disk0/sdc/multipath/
> total 0
> lrwxrwxrwx 1 root root 0 Feb 25 12:00 sdc:0 ->
> ../../../../../platform/host8/session1/target8:0:0/8:0:0:0/block/sdc:0
> lrwxrwxrwx 1 root root 0 Feb 25 12:00 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 25 11:58 /dev/sdc
>
> The scsi_device and scsi_disk classes otherwise remain unmodified.
> However, the per-path block device is hidden in /dev/. Furthermore,
> multipathed block devices have a new naming scheme, sdX:Y, where
> X is the scsi multipath device index and Y is the path index.
>
> No multipath sg support is added. We still have a per-path sg device.
> Since the SCSI block device is multipath enabled, we can access
> multipathed scsi_ioctl() through that block device.
>
> For failover, we take the approach of cloning bio's and re-submitting them
> in full (for failover errors).
>
> LIBMULTIPATH:
>
> This series introduces also libmultipath. It is essentially a refactoring
> of NVME multipath support, so we can have a common library to also support
> native SCSI multipath.
>
> Much of the code is taken directly from the NVMe multipath code. However,
> NVMe specifics are removed. A template structure is provided so the driver
> -may provide callbacks for driver specifics, like ANA support for NVMe.
>
> Important new structures introduced include:
>
> - mpath_head
> These contain much of the multipath-specific functionality from
> nvme_ns_head, including a pointer to the gendisk structure and
> a path SRCU-based array.
>
> - mpath_device
> This is the per-path structure, and contains much the same
> multipath-specific functionality in nvme_ns
>
> libmultipath provides functionality for path management, path selection,
> data path, and failover handling.
>
> Full series also available at
> https://github.com/johnpgarry/linux/commits/scsi-multipath-v7.3-v8/
>
> Differences to v7:
> - rebase
> - simplify scsi_mpath_clone_end_io() (sashiko)
> - rename bio_list_add_clone() -> bio_list_add_master()
> - rework checks in mpath_alloc_disk_head() (sashiko)
>
> Differences to v6:
> - rebase
> - add scsi_mpath_get_head()
>
> Differences to v5:
> - deal with issues sashiko found in libmultipath:
> - include wait_bit.h
> - don't store error in mpath_head->disk
> - use check_mul_overflow() in mpath_can_remove_head()
> - use -ENOTTY in mpath_bdev_ioctl()
> - deal with issues sashiko found in scsi mpath support:
> - check 0 returned from scsi_vpd_lun_id()
> - call flush_work() in scsi_mpath_device_iopolicy_store()
> - clear SCMD_MPATH_IO_STATS for !bio in scsi_mpath_start_request()
> - add checks for calling scsi_mpath_{start,end}_request()
> - tweak sd_mpath_dev_show()
>
> John Garry (27):
> libmultipath: Add initial framework
> libmultipath: Add basic gendisk support
> libmultipath: Add path selection support
> libmultipath: Add bio handling
> libmultipath: Add support for mpath_device management
> libmultipath: Add delayed removal support
> libmultipath: Add sysfs helpers
> libmultipath: Add support for block device IOCTL
> libmultipath: Add mpath_bdev_getgeo()
> libmultipath: Add mpath_bdev_get_unique_id()
> scsi-multipath: introduce basic SCSI device support
> scsi-multipath: introduce scsi_device head structure
> scsi-multipath: provide sysfs link from to scsi_device
> scsi-multipath: support iopolicy
> scsi-multipath: clone each bio
> scsi-multipath: clear path when device is blocked
> scsi-multipath: revalidate paths upon device unblock
> scsi-multipath: failover handling
> scsi-multipath: provide callbacks for path state
> scsi-multipath: add scsi_mpath_{start,end}_request()
> scsi-multipath: add delayed disk removal support
> scsi: sd: add multipath disk class
> scsi: sd: add multipath disk attr groups
> scsi: sd: support multipath disk
> scsi: sd: add mpath_dev file
> scsi: sd: add mpath_numa_nodes dev attribute
> scsi: sd: add mpath_queue_depth dev attribute
>
> drivers/scsi/Kconfig | 10 +
> drivers/scsi/Makefile | 1 +
> drivers/scsi/scsi.c | 8 +-
> drivers/scsi/scsi_lib.c | 13 +-
> drivers/scsi/scsi_multipath.c | 664 ++++++++++++++++++++++++
> drivers/scsi/scsi_scan.c | 4 +
> drivers/scsi/scsi_sysfs.c | 10 +
> drivers/scsi/sd.c | 611 +++++++++++++++++++++-
> drivers/scsi/sd.h | 3 +
> include/linux/multipath.h | 156 ++++++
> include/scsi/scsi_cmnd.h | 9 +-
> include/scsi/scsi_device.h | 2 +
> include/scsi/scsi_driver.h | 4 +
> include/scsi/scsi_host.h | 4 +
> include/scsi/scsi_multipath.h | 124 +++++
> lib/Kconfig | 6 +
> lib/Makefile | 2 +
> lib/multipath.c | 947 ++++++++++++++++++++++++++++++++++
> 18 files changed, 2554 insertions(+), 24 deletions(-)
> create mode 100644 drivers/scsi/scsi_multipath.c
> create mode 100644 include/linux/multipath.h
> create mode 100644 include/scsi/scsi_multipath.h
> create mode 100644 lib/multipath.c
>
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