Adding support of quirky filesystems occuring in virtualised settings not
having full POSIX support for memory mapped files. Example: current virtiofs
with cache disabled, occuring in Incus/LXD or Kata Containers. Has been
hitting various virtualised filesystems since 2016, depending on their levels
of maturity at the time. The situation will perhaps improve when virtiofs DAX
support patches will have made it into the qemu mainline.
On a reliability level, using the MAP_PRIVATE sycall flag instead of the
MAP_SHARED syscall flag for the mmap() system call does have some undefined
behaviour when the caller update the memory mapping of the mmap()ed file, but
MAP_SHARED does allow not only the calling process but other processes to
modify the memory mapping. Thus, in the current context, using MAP_PRIVATE
copy-on-write is marginally more reliable than MAP_SHARED.
This discussion of reliability is orthogonal to the type system enforced safety
policy of rust, which does not claim to handle memory modification of memory
mapped files triggered through the operating system and not the running rust
process.
Turns out
- `owning_ref` is unsound due to `Box` aliasing stuff
- `rustc` doesn't need 99% of the `owning_ref` API
- `rustc` can use a far simpler abstraction that is `OwnedSlice`
Rollup of 9 pull requests
Successful merges:
- #104199 (Keep track of the start of the argument block of a closure)
- #105050 (Remove useless borrows and derefs)
- #105153 (Create a hacky fail-fast mode that stops tests at the first failure)
- #105164 (Restore `use` suggestion for `dyn` method call requiring `Sized`)
- #105193 (Disable coverage instrumentation for naked functions)
- #105200 (Remove useless filter in unused extern crate check.)
- #105201 (Do not call fn_sig on non-functions.)
- #105208 (Add AmbiguityError for inconsistent resolution for an import)
- #105214 (update Miri)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
