block: add a sequence number to disks

From:		Matteo Croce <mcroce-AT-linux.microsoft.com>
To:		linux-block-AT-vger.kernel.org, linux-fsdevel-AT-vger.kernel.org
Subject:		[PATCH 0/5] block: add a sequence number to disks
Date:		Sat, 06 Feb 2021 01:08:58 +0100
Message-ID:		<20210206000903.215028-1-mcroce@linux.microsoft.com>
Cc:		linux-kernel-AT-vger.kernel.org, Lennart Poettering <lennart-AT-poettering.net>, Luca Boccassi <bluca-AT-debian.org>, Jens Axboe <axboe-AT-kernel.dk>, Alexander Viro <viro-AT-zeniv.linux.org.uk>
Archive-link:		Article

From: Matteo Croce <mcroce@microsoft.com>

With this series a monotonically increasing number is added to disks,
precisely in the genhd struct, and it's exported in sysfs and uevent.

This helps the userspace correlate events for devices that reuse the
same device, like loop.

The first patch is the core one, the 2..4 expose the information in
different ways, while the last one increase the sequence number for
loop devices at every attach.

    # udevadm monitor -kp |grep -e ^DEVNAME -e ^DISKSEQ &
    [1] 523
    # losetup -fP 3part
    [ 3698.615848] loop0: detected capacity change from 16384 to 0
    DEVNAME=/dev/loop0
    DISKSEQ=13
    [ 3698.647189]  loop0: p1 p2 p3
    DEVNAME=/dev/loop0
    DISKSEQ=13
    DEVNAME=/dev/loop0p1
    DISKSEQ=13
    DEVNAME=/dev/loop0p2
    DISKSEQ=13
    DEVNAME=/dev/loop0p3
    DISKSEQ=13
    # losetup -fP 2part
    [ 3705.170766] loop1: detected capacity change from 40960 to 0
    DEVNAME=/dev/loop1
    DISKSEQ=14
    [ 3705.247280]  loop1: p1 p2
    DEVNAME=/dev/loop1
    DISKSEQ=14
    DEVNAME=/dev/loop1p1
    DISKSEQ=14
    DEVNAME=/dev/loop1p2
    DISKSEQ=14
    # ./getdiskseq /dev/loop*
    /dev/loop0:     13
    /dev/loop0p1:   13
    /dev/loop0p2:   13
    /dev/loop0p3:   13
    /dev/loop1:     14
    /dev/loop1p1:   14
    /dev/loop1p2:   14
    /dev/loop2:     5
    /dev/loop3:     6
    /dev/loop-control: Function not implemented
    # grep . /sys/class/block/*/diskseq
    /sys/class/block/loop0/diskseq:13
    /sys/class/block/loop1/diskseq:14
    /sys/class/block/loop2/diskseq:5
    /sys/class/block/loop3/diskseq:6
    /sys/class/block/ram0/diskseq:1
    /sys/class/block/ram1/diskseq:2
    /sys/class/block/vda/diskseq:7

If merged, this feature will immediately used by the userspace:
https://github.com/systemd/systemd/issues/17469#issuecomm...

Matteo Croce (5):
  block: add disk sequence number
  block: add ioctl to read the disk sequence number
  block: refactor sysfs code
  block: export diskseq in sysfs
  loop: increment sequence number

 Documentation/ABI/testing/sysfs-block | 12 ++++++++
 block/genhd.c                         | 43 ++++++++++++++++++++++++---
 block/ioctl.c                         |  2 ++
 drivers/block/loop.c                  |  3 ++
 include/linux/genhd.h                 |  2 ++
 include/uapi/linux/fs.h               |  1 +
 6 files changed, 59 insertions(+), 4 deletions(-)

-- 
2.29.2