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    Subject[-v3 PATCH 0/3] Persistent device name using alias
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    Hi,

    This patch series provide an "alias" of the disk into kernel messages.

    A raw device name of a disk does not always point a same disk at each boot-up
    time. Therefore, users have to use persistent device names, which udev creates
    to always access the same disk. However, kernel messages still display the raw
    device names.

    My proposal is that users can use and see persistent device names which were
    assigned by themselves because users expect same name to point same disk
    anytime.

    Why need to modify kernel messages?
    - We can see mapping of device names and persistent device names in udev log.
    If those logs output to syslog, we can search persistent device name from
    device name, but it can cause a large amount of syslog output.

    - If we can use the persistent device names and can always see the same name on
    the kernel log, we don't need to pay additional cost for searching and picking
    a correct pair of device name and persistent device name from udev log.

    - Kernel messages are output to serial console when kenel crashes, it's so hard
    to convert a device name to the alias.

    Of course, I am going to modify the commands using device name so that users
    can use an alias of the disk.

    Changes in v3:
    - "alias_name" was changed to "alias"
    - The function to notify the partitions of uevent was deleted


    How to use:
    1. Build and install the kernel with this series, and reboot with the kernel.

    2. Check device names.

    [localhost]# cat /proc/partitions
    major minor #blocks name

    8 0 12582912 sda
    8 1 12582878 sda1
    8 0 8388608 sdb
    8 1 512000 sdb1
    8 2 7875584 sdb2


    3. Make a script of get alias

    [localhost]# vi /lib/udev/get_alias
    #!/bin/sh -e
    DEVNAME=`echo $1 | sed -e 's/[0-9]//g'`
    echo "ALIAS=`cat /sys/block/$DEVNAME/alias`"
    exit 0

    And you should set an execute bit,
    [localhost]# chmod +x /lib/udev/get_alias

    4. Check disk's id
    Here is an example to get the serial id and the path of the device.
    Some devices have not the serial id. Therefore, to identify a device,
    users need to get the path of the device.

    [localhost]# udevadm info --query=property --path=/sys/block/sda \
    | grep ID_SERIAL=
    ID_SERIAL=0QEMU_QEMU_HARDDISK_drive-scsi0-0-1

    or you can also use the path of the device

    [localhost]# udevadm info --query=property --path=/sys/block/sr0 \
    | grep ID_PATH=
    ID_PATH=pci-0000:00:01.1-scsi-1:0:0:0


    5. Write udev rules as follows
    (The user assigns "foo" to sda and "bar" to sr0)
    We use ENV{ID_SERIAL} or ENV{ID_PATH} (get by 3) to identify a disk.
    And to assign automatically an "alias", we use ATTR key.
    If ENV{ALIAS} is empty, we use to get an "alias" by get_alias script.

    [localhost]# vi /etc/udev/rules.d/70-persistent-alias.rules
    SUBSYSTEM!="block", GOTO="end"
    ATTR{alias}!="", GOTO="symlink"

    # write alias for sdX
    KERNEL=="sd*[!0-9]", ACTION=="add", ATTR{alias}="foo", \
    ENV{ID_SERIAL}=="0QEMU_QEMU_HARDDISK_drive-scsi0-0-1"

    # write alias for srX
    KERNEL=="sr[0-9]", ACTION=="add", ATTR{alias}="bar", \
    ENV{ID_PATH}=="pci-0000:00:01.1-scsi-1:0:0:0"

    LABEL="symlink"

    # make symlink
    ENV{DEVTYPE}=="disk|partition", ENV{ALIAS}=="", \
    IMPORT{program}="/lib/udev/get_alias %k"
    ENV{DEVTYPE}=="disk", ENV{ALIAS}=="?*", SYMLINK+="disk/by-alias/$env{ALIAS}"
    ENV{DEVTYPE}=="partition", ENV{ALIAS}=="?*", \
    SYMLINK+="disk/by-alias/$env{ALIAS}%n"

    LABEL="end"


    6. reboot
    After reboot, we can see aliases in kernel messages.

    [localhost]# ls -l /dev/disk/by-alias/
    total 0
    lrwxrwxrwx. 1 root root 9 Jul 1 21:21 bar -> ../../sr0
    lrwxrwxrwx. 1 root root 9 Jul 1 21:21 foo -> ../../sda
    lrwxrwxrwx. 1 root root 10 Jul 1 21:21 foo1 -> ../../sda1

    [localhost]# dmesg
    ...
    sd 2:0:1:0: [sda] Attached SCSI disk
    alias: assigned foo to sda
    sd 2:0:1:0: [foo] Send: 0xffff88007a82cd00
    sd 2:0:1:0: [foo] CDB: Write(10): 2a 00 01 58 0c 8a 00 00 08 00
    buffer = 0xffff88007a82c500, bufflen = 4096, queuecommand 0xffffffffa00277fd
    leaving scsi_dispatch_cmnd()
    sd 2:0:1:0: [foo] Done: 0xffff88007a82cd00 SUCCESS
    sd 2:0:1:0: [foo] Result: hostbyte=DID_OK driverbyte=DRIVER_OK
    sd 2:0:1:0: [foo] CDB: Write(10): 2a 00 01 58 0c 8a 00 00 08 00
    ...

    When a new device is added, the udev appends a new rule manually.
    In the future, it is appended automatically, as like NIC.

    Best Regards,

    ---

    Joe Perches (1):
    sd: modify printk for alias name

    Nao Nishijima (2):
    sd: [cleanup] Use sd_printk() instead of printk()
    block: add a new attribute "alias" in gendisk


    Documentation/ABI/testing/sysfs-block | 13 ++++++
    block/genhd.c | 71 +++++++++++++++++++++++++++++++++
    drivers/scsi/scsi_lib.c | 26 ++++++++++++
    drivers/scsi/sd.c | 30 +++++++++++++-
    drivers/scsi/sd.h | 8 +---
    include/linux/genhd.h | 4 ++
    include/scsi/scsi_device.h | 8 +---
    7 files changed, 147 insertions(+), 13 deletions(-)


    --
    Nao Nishijima (nao.nishijima.xt@hitachi.com)


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