On Fri, 2020-02-14 at 19:35 +0100, Christian Brauner wrote: [...] > People not as familiar with user namespaces might not be aware that > fsid mappings already exist. Right now, fsid mappings are always > identical to id mappings. Specifically, the kernel will lookup fsuids > in the uid mappings and fsgids in the gid mappings of the relevant > user namespace. This isn't actually entirely true: today we have the superblock user namespace, which can be used for fsid remapping on filesystems that support it (currently f2fs and fuse). Since this is a single shift, how is it going to play with s_user_ns? Do you have to understand the superblock mapping to use this shift, or are we simply using this to replace s_user_ns? James
