forked from lix-project/lix
cc63db1dd5
It is surprisingly impossible to check if a mountpoint is a bind mount on Linux, and in my previous commit I forgot to check if /nix/store was even a mountpoint at all. statvfs.f_flag is not populated with MS_BIND (and even if it were, my check was wrong in the previous commit). Luckily, the semantics of mount with MS_REMOUNT | MS_BIND make both checks unnecessary: if /nix/store is not a mountpoint, then mount will fail with EINVAL, and if /nix/store is not a bind-mount, then it will not be made writable. Thus, if /nix/store is not a mountpoint, we fail immediately (since we don't know how to make it writable), and if /nix/store IS a mountpoint but not a bind-mount, we fail at first write (see below for why we can't check and fail immediately). Note that, due to what is IMO buggy behavior in Linux, calling mount with MS_REMOUNT | MS_BIND on a non-bind readonly mount makes the mountpoint appear writable in two places: In the sixth (but not the 10th!) column of mountinfo, and in the f_flags member of struct statfs. All other syscalls behave as if the mount point were still readonly (at least for Linux 3.9-rc1, but I don't think this has changed recently or is expected to soon). My preferred semantics would be for MS_REMOUNT | MS_BIND to fail on a non-bind mount, as it doesn't make sense to remount a non bind-mount as a bind mount. |
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| .. | ||
| build.cc | ||
| derivations.cc | ||
| derivations.hh | ||
| gc.cc | ||
| globals.cc | ||
| globals.hh | ||
| local-store.cc | ||
| local-store.hh | ||
| Makefile.am | ||
| misc.cc | ||
| misc.hh | ||
| optimise-store.cc | ||
| pathlocks.cc | ||
| pathlocks.hh | ||
| references.cc | ||
| references.hh | ||
| remote-store.cc | ||
| remote-store.hh | ||
| schema.sql | ||
| store-api.cc | ||
| store-api.hh | ||
| worker-protocol.hh | ||