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udev: add flag to allow disabling blkid probing

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This can be useful for users of slow block devices.

For example, the persistent-storage rules are needed for USB floppy
drives be recognized by udisks2, but the extra blkid calls cause
thrashing for 25+ seconds after every disk change.

With this change, a user wishing to avoid the extra blkid invocation(s)
could create /etc/udev/rules.d/55-floppy-noprobe.rules as follows:

    # Don't probe PC floppy drives
    SUBSYSTEM=="block", KERNEL=="fd*", \
        ENV{UDEV_DISABLE_PERSISTENT_STORAGE_BLKID_FLAG}="1"

    # Don't probe USB floppy drives
    SUBSYSTEM=="block", SUBSYSTEMS=="usb", \
        ATTRS{bInterfaceClass}=="08", ATTRS{bInterfaceSubClass}=="04", \
        ENV{UDEV_DISABLE_PERSISTENT_STORAGE_BLKID_FLAG}="1"

I didn't exclude floppies by default in this change, because floppy
devices are also emulated by some BIOSes/hypervisors in some cases, and
I don't know how many systems would fail to boot if /dev/disk/by-uuid/*
became unavailable for 'floppy disks' on those systems.
This commit is contained in:
Darsey Litzenberger 2022-07-10 21:47:45 -07:00 committed by Yu Watanabe
parent c043291774
commit b5e17d7fed
1 changed files with 5 additions and 0 deletions
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5
rules.d/60-persistent-storage.rules
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@ -99,6 +99,9 @@ ENV{DEVTYPE}=="partition", ENV{ID_PATH_ATA_COMPAT}=="?*", SYMLINK+="disk/by-path
KERNEL=="vd*[!0-9]", ENV{ID_PATH}=="pci-*", SYMLINK+="disk/by-path/virtio-$env{ID_PATH}"
KERNEL=="vd*[0-9]", ENV{ID_PATH}=="pci-*", SYMLINK+="disk/by-path/virtio-$env{ID_PATH}-part%n"
# allow admin to disable probing the filesystem for slow devices like floppy disk drives
ENV{UDEV_DISABLE_PERSISTENT_STORAGE_BLKID_FLAG}=="1", GOTO="persistent_storage_blkid_probe_end"
# probe filesystem metadata of optical drives which have a media inserted
KERNEL=="sr*", ENV{DISK_EJECT_REQUEST}!="?*", ENV{ID_CDROM_MEDIA_TRACK_COUNT_DATA}=="?*", ENV{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}=="?*", \
IMPORT{builtin}="blkid --hint=session_offset=$env{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}"
@ -109,6 +112,8 @@ KERNEL=="sr*", ENV{DISK_EJECT_REQUEST}!="?*", ENV{ID_CDROM_MEDIA_TRACK_COUNT_DAT
# probe filesystem metadata of disks
KERNEL!="sr*|mmcblk[0-9]boot[0-9]", IMPORT{builtin}="blkid"
LABEL="persistent_storage_blkid_probe_end"
# by-label/by-uuid links (filesystem metadata)
ENV{ID_FS_USAGE}=="filesystem|other|crypto", ENV{ID_FS_UUID_ENC}=="?*", SYMLINK+="disk/by-uuid/$env{ID_FS_UUID_ENC}"
ENV{ID_FS_USAGE}=="filesystem|other|crypto", ENV{ID_FS_LABEL_ENC}=="?*", SYMLINK+="disk/by-label/$env{ID_FS_LABEL_ENC}"