On Wed, Aug 23, 2023 at 05:34:06PM +0200, David Hildenbrand wrote: > Currently, if a file does not exist yet, file_ram_open() will create new > empty file and open it writable. However, it even does that when > readonly=true was specified. > > Specifying O_RDONLY instead to create a new readonly file would > theoretically work, however, ftruncate() will refuse to resize the new > empty file and we'll get a warning: > ftruncate: Invalid argument > And later eventually more problems when actually mmap'ing that file and > accessing it. > > If someone intends to let QEMU open+mmap a file read-only, better > create+resize+fill that file ahead of time outside of QEMU context. > > We'll now fail with: > ./qemu-system-x86_64 \ > -object memory-backend-file,id=ram0,mem-path=tmp,readonly=true,size=1g > qemu-system-x86_64: can't open backing store tmp for guest RAM: No such file > or directory > > All use cases of readonly files (R/O NVDIMMs, VM templating) work on > existing files, so silently creating new files might just hide user > errors when accidentally specifying a non-existent file. > > Note that the only memory-backend-file will end up calling > memory_region_init_ram_from_file() -> qemu_ram_alloc_from_file() -> > file_ram_open(). > > Move error reporting to the single caller. > > Signed-off-by: David Hildenbrand <da...@redhat.com>
Acked-by: Peter Xu <pet...@redhat.com> -- Peter Xu