Each edit planned over the reader's memory map of the file and committed
while that File, and the Image's &[u8] over the mapping, were still alive,
writing the same file through the editor's descriptor. Nothing read the
mapping during the writes, but a shared slice whose memory changes
underneath it is undefined behaviour under Rust's aliasing rules.
Image::into_plan now detaches the edit's writes (patches, end of
allocation) into a Plan that owns all of its bytes and borrows nothing;
edit() takes the user-block size, drops the File — unmapping the file —
and only then commits the Plan. The invariant is documented in the image
module and the editor's module docs.
Test: edit::tests::file_is_not_mapped_while_an_edit_writes_it checks
/proc/self/maps at the moment each commit starts (write, resize, set_attr):
never mapped. With the commit moved back before the reader is dropped (the
previous order) it reports all three commits with the file mapped.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
