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+permissions: 0.983
+mistranslation: 0.968
+boot: 0.943
+files: 0.933
+performance: 0.922
+device: 0.890
+graphic: 0.882
+semantic: 0.851
+peripherals: 0.814
+architecture: 0.809
+debug: 0.699
+ppc: 0.647
+user-level: 0.601
+x86: 0.579
+i386: 0.568
+network: 0.560
+PID: 0.557
+vnc: 0.547
+risc-v: 0.539
+hypervisor: 0.483
+register: 0.477
+VMM: 0.470
+kernel: 0.434
+arm: 0.427
+TCG: 0.412
+socket: 0.305
+assembly: 0.287
+virtual: 0.282
+KVM: 0.270
+
+memory backend file unnecessarily requires write permission while it is only mapped privately
+Description of problem:
+One day I wanted to boot the machine with physical memory initialized with a file, in a copy-on-write style. That is why I tried out `-mem-path` and `-object memory-backend-file`. Actually `-mem-path` already works if not considering that qemu dislikes the backing file being readonly and requires it to be writeable even when only private mappings are used here.
+
+I sadly found out that when using memory-backend-file, and when `share=off`, if `readonly=on`, then file is `open`ed with `O_RDONLY` and mmap prot is `PROT_READ`; if `readonly=off`, then the file is `open`ed with `O_RDWR` and mmap prot is `PROT_READ|PROT_WRITE`. I want `O_RDONLY` and `PROT_READ|PROT_WRITE` but I cannot find it anywhere.
+
+In my opinion, expected behavior should be that if `share=off`, the file can already be opened with `O_RDONLY` no matter what prot the mmap is. That is how linux `MAP_PRIVATE` works - basically copy on write. When I only need copy on write for the content of file, why do I require write permission for it?
+
+Now I cannot find a setup that opens the file with `fd=open(*, O_RDONLY)` and mmap it with `mmap(*, *, PROT_READ|PROT_WRITE, MAP_PRIVATE|*, fd, *)`.
+
+Tell me if I misunderstood linux (for example certain file behave differently if one open with O_RDONLY and this behavior is necessary) or qemu or other posix systems where copy-on-write does not work like this.