Its purpose was to translate the values for msdosfs inode numbers,
which is calculated from the msdosfs structures describing the file,
into the range representable by 32bit ino_t. The translation acted
for filesystems larger than 128Gb, it reserved the range 0xf0000000
(FILENO_FIRST_DYN) to UINT32_MAX and remembered some arbitrary
translation of ino >= FILENO_FIRST_DYN into this range. It consumed
memory that could be only freed by unmount, and the translation was
not stable across remounts.
With ino_t type extended to 64 bit, there is no such issue and values
can be returned without compaction to 32bit. That is, for the native
environments, the translation layer is not necessary and adds
significant undeserved code complexity. For compat ABIs which use
32bit ino_t, the vfs.ino64_trunc_error sysctl provides some measures
to soften the failure mode when inode numbers truncation is not safe.
Discussed with: bde
Sponsored by: The FreeBSD Foundation
40373cf5b8