Zbigniew Jędrzejewski-Szmek
d8646d0572
We cannot compare filenames directly, because paths are not sortable lexicographically, e.g. /etc/udev is "later" (has higher priority) than /usr/lib/udev. The on-disk format is changed to have a separate field for "file priority", which is stored when writing the binary file, and then loaded and used in comparisons. For data in the previous format (as generated by systemd 232), this information is not available, and we use a trick where the offset into the string table is used as a proxy for priority. Most of the time strings are stored in the order in which the files were processed. This is not entirely reliable, but is good enough to properly order /usr/lib and /etc/, which are the two most common cases. This hack is included because it allows proper parsing of files until the binary hwdb is regenerated. Instead of adding a new field, I reduced the size of line_number from 64 to 32 bits, and added a 16 bit priority field, and 16 bits of padding. Adding a new field of 16 bytes would significantly screw up alignment and increase file size, and line number realistically don't need more than ~20 bits. Fixes #4750.
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