[PATCH v8 00/27] Native SCSI Multipath support

[John Garry <john.g.garry@oracle.com>]

NATIVE SCSI MULTIPATH:

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

-- 
2.43.7