More reliable vendor/serial/path extraction via udev

[jpo-joyent]

Ghw is currently relying on udev's population of /dev/disk/by-id/... to extract serial information (see https://github.com/jaypipes/ghw/blob/85a00ff/block_linux.go#L80-L129). This means two things:

• parsing serial numbers themselves containing - or _ can lead to incorrect results
• we already have a dependency on udev

Udev also exposes this information in a less-ambiguous less-fragile-to-parse way under /run/udev/data/....

This data is indexed by major:minor device numbers, which can be found by e.g.:

$ cat /sys/class/block/sdj/dev
8:144

(or just stating the device node under /dev/...)

Then, you have convenient access to all of:

$ cat /run/udev/data/b8:144
S:disk/by-id/scsi-35000cca08062c3d4
S:disk/by-id/wwn-0x5000cca08062c3d4
S:disk/by-path/pci-0000:03:00.0-sas-0x5000cca08062c3d5-lun-0
S:disk/by-path/pci-0000:03:00.0-sas-exp0x500056b3896bccff-phy8-lun-0
W:34
I:414515
E:ID_BUS=scsi
E:ID_FS_TYPE=
E:ID_MODEL=HUC101812CSS200
E:ID_MODEL_ENC=HUC101812CSS200\x20
E:ID_PATH=pci-0000:03:00.0-sas-0x5000cca08062c3d5-lun-0
E:ID_PATH_TAG=pci-0000_03_00_0-sas-0x5000cca08062c3d5-lun-0
E:ID_REVISION=FU29
E:ID_SAS_PATH=pci-0000:03:00.0-sas-exp0x500056b3896bccff-phy8-lun-0
E:ID_SCSI=1
E:ID_SCSI_SERIAL=0EHS9UWF
E:ID_SERIAL=35000cca08062c3d4
E:ID_SERIAL_SHORT=5000cca08062c3d4
E:ID_TYPE=disk
E:ID_VENDOR=HGST
E:ID_VENDOR_ENC=HGST\x20\x20\x20\x20
E:ID_WWN=0x5000cca08062c3d4
E:ID_WWN_WITH_EXTENSION=0x5000cca08062c3d4
E:MPATH_SBIN_PATH=/sbin
G:systemd

Still all as non-root ;)

[jaypipes]

@jpo-joyent Hi! This is awesome information! :) Wish I had known about it earlier.

I'll see what I can do about using these new filepaths for grabbing information about block devices (and other devices).

Thanks so much!