Al Viro: > I'd managed to push that particular nest of horrors out of mind ;-/ > Having dug out my notes from back then and grepped around... The real > mess is not even /proc/*/maps - it's /proc/*/map_files/* and yes, the > reasons for that kludge are still valid ;-/ ::: > Uses of ->vm_file (and rules for those) are too convoluted to untangle > at the moment. I still would love to get that straightened out, but > it's not this cycle fodder, more's the pity... I don't fully read this thread, but the discussion is related to the file path printed in /proc/$$/maps? If so, as just for your information, here is an approach that aufs took. In linux-v2.6 era, aufs tried implementing mmap by customzing address_space ops, but it was not good and failed completing the implementation. As wel as overlayfs, aufs has two struct file objects for a single a regular file. One is for a virtual aufs' entry, and the other is for a real layer's entry. When a user issues mmap(2) for the virtual file, aufs redirects the request to the real file on the layer internally. So the vm_file points to the real file. It means /proc/$$/maps prints the unexpected file path. Aufs added another struct file* vm_prfile in struct vma. It points to the virtual aufs file, and /proc/$$/maps prints vm_prfile instead of vm_file. Of cource, maintaining vm_prfile is important since vma may be merged or splitted. Still I don't like this approach, but I don't have another better idea, also it works for many years. You can get the patch in aufs4-standalone.git on sourceforge if you want. J. R. Okajima
