Dne 09. 03. 25 v 17:00 Zack Weinberg napsal(a):
I am developing a device-mapper client library in Rust. The language is
relevant here because Rust's standard library makes a strong distinction
between strings that are known to be encoded in UTF-8 and strings whose
encoding is not known (`str` vs `OsStr`), with the latter being awkward
to use compared to the former.
The device-mapper ioctls use a lot of strings, and it's not clear
to me from either the documentation or the kernel's source code
what expectations the *kernel* has of the character encoding of these
strings. I don't expect the kernel to care about UTF-8 versus
ISO-8859-n or whatever, but it is plausible to me that at least some
of the strings used in device-mapper ioctls can be expected always to
be ASCII, in which case I can safely use `str` for them on the library
side and it'll be more ergonomic for end users.
Hi
While you could surely interface kernel directly through ioctl(),
you should probably base your tool around libdevmapper as this library
is there to solve version differences or possible kernel or udev
issue that pops up here and there - if you will go your own path,
you will need to reimplement these things within Rust - which
might potentially be problematic - as we are solving i.e. udev trouble
to be working only within our 'small world' across different version of kernel
and udev version installed on the system.
There are, I think, four different kinds of strings used in device-
mapper ioctls: target names, device names and UUIDs, table parameters,
and target messages. For each of these, I would like to ask:
Device name and UUID are always plain 7bit ASCII.
But there is a catch in udev process - as udev has even further limited char
subset usable for device names - libdevmapper uses name mangling for those.
Again - you are free to reimplement your Rust version - but eventually this
may lead to a completely different set of udev rules needed for management of
Rust devices - as libdevmapper is free to 'change' DM udev rules as long as
we are 'internally' consistent - as these rules are seen as 'internal'
property for DM world.
Regards
Zdenek
