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udev-builtin-blkid: add support for --hint offsets

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The next libblkid v2.37 is going to support session offsets for
multi-session CD/DVDs. This feature is implemented by "hint offsets".

These offsets are optional and prober specific (e.g., iso, udf, ...).
For this purpose, the library provides a new function
blkid_probe_set_hint(), and blkid(8) provides a new command-line
option --hint <name>=<offset>. For CD/DVD, the offset name is
"session_offset".

The difference between classic --offset and the new --hint is that
--offset is very restrictive and defines the probing area and the rest
of the device is invisible to the library. The new --hint works
like a suggestion, it provides a hint where the user assumes the
filesystem, but the rest of the device is still readable for the
library (for example, to get some additional superblock information
etc.).

If the --hint is without a value then it defaults to zero.

The option --hint implementation in udev-builtin-blkid.c is backwardly
compatible. If compiled against old libblkid, then the option is used in
the same way as --offset.

Addresses: https://github.com/karelzak/util-linux/issues/1161
Addresses: https://github.com/systemd/systemd/pull/17424
This commit is contained in:
Karel Zak
2021-01-13 00:58:43 +09:00
committed by Yu Watanabe
parent 885598f36c
commit 4fcc033b54
4 changed files with 30 additions and 10 deletions
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test/fuzz/fuzz-udev-rules/60-persistent-storage.rules
+1 -1
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@@ -86,7 +86,7 @@ KERNEL=="vd*[0-9]", ENV{ID_PATH}=="pci-*", SYMLINK+="disk/by-path/virtio-$env{ID
# probe filesystem metadata of optical drives which have a media inserted
KERNEL=="sr*", ENV{DISK_EJECT_REQUEST}!="?*", ENV{ID_CDROM_MEDIA_TRACK_COUNT_DATA}=="?*", ENV{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}=="?*", \
IMPORT{builtin}="blkid --offset=$env{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}"
IMPORT{builtin}="blkid --hint=session_offset=$env{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}"
# single-session CDs do not have ID_CDROM_MEDIA_SESSION_LAST_OFFSET
KERNEL=="sr*", ENV{DISK_EJECT_REQUEST}!="?*", ENV{ID_CDROM_MEDIA_TRACK_COUNT_DATA}=="?*", ENV{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}=="", \
IMPORT{builtin}="blkid --noraid"