Hello, Currently the only way to iterate over mount entries in mount namespaces that aren't your own is to trawl through /proc in order to find /proc/$PID/mountinfo for the mount namespace that you want. This is hugely inefficient, so extend both statmount() and listmount() to allow specifying a mount namespace id in order to get to mounts in other mount namespaces. There are a few components to this 1. Having a global index of the mount namespace based on the ->seq value in the mount namespace. This gives us a unique identifier that isn't re-used. 2. Support looking up mount namespaces based on that unique identifier, and validating the user has permission to access the given mount namespace. 3. Provide a new ioctl() on nsfs in order to extract the unique identifier we can use for statmount() and listmount(). The code is relatively straightforward, and there is a selftest provided to validate everything works properly. This is based on vfs.all as of last week, so must be applied onto a tree that has Christians error handling rework in this area. If you wish you can pull the tree directly here https://github.com/josefbacik/linux/tree/listmount.combined Christian and I collaborated on this series, which is why there's patches from both of us in this series. Josef Christian Brauner (4): fs: relax permissions for listmount() fs: relax permissions for statmount() fs: Allow listmount() in foreign mount namespace fs: Allow statmount() in foreign mount namespace Josef Bacik (4): fs: keep an index of current mount namespaces fs: export the mount ns id via statmount fs: add an ioctl to get the mnt ns id from nsfs selftests: add a test for the foreign mnt ns extensions fs/mount.h | 2 + fs/namespace.c | 240 ++++++++++-- fs/nsfs.c | 14 + include/uapi/linux/mount.h | 6 +- include/uapi/linux/nsfs.h | 2 + .../selftests/filesystems/statmount/Makefile | 2 +- .../filesystems/statmount/statmount.h | 46 +++ .../filesystems/statmount/statmount_test.c | 53 +-- .../filesystems/statmount/statmount_test_ns.c | 360 ++++++++++++++++++ 9 files changed, 659 insertions(+), 66 deletions(-) create mode 100644 tools/testing/selftests/filesystems/statmount/statmount.h create mode 100644 tools/testing/selftests/filesystems/statmount/statmount_test_ns.c -- 2.43.0
