Hi, I did the following experiment wrt mmap and qemu (v2.3) and noticed a strange behavior. Can anyone explain if this is expected (or perhaps a bug?).
I have a program which opens a file and mmaps the file contents into a private memory space. My program is same as http://beej.us/guide/bgipc/examples/mmapdemo.c, with only change - MAP_PRIVATE instead of MAP_SHARED. If MAP_PRIVATE is used, ideally the mmap-ed region contents even if changed, must never be written back to the disk. In my example, the driver program does NOT do any writing at all. It simply opens a read-only file and creates a new read-only mmap-ed space supported by that file. However, I do the writing differently from my QEMU emulation. I catch the mmap address returned in helper_sysret() and also capture the translated host virtual address (X) corresponding to that. Then corrupt the data from X to say X + 10 addresses. I notice that this causes the original file to be corrupted as well. So ideally the contents written must never reach the disk right? Since it is equivalent to a write (from driver program) in MAP_PRIVATE region. Let me know if you want the actual source code diff for reproducing this. Thanks, Viswesh
