Hi Ian, On Thu, Jun 07, 2018 at 08:47:28AM +0800, Ian Kent wrote: > On Wed, 2018-06-06 at 23:38 +0200, Mark Fasheh wrote: > > Hi, > > I'm not sure I understand what the problem is. I'll try to elaborate below. > > We have an inconsistency in how the kernel is exporting inode number / > > device pairs for user space. There's of course stat(2) and statx(2), > > but aside from those we simply dump inode->i_ino and super->s_dev. In > > some cases, the dumped values differ from what is returned via stat(2) > > or statx(2). Some filesystems might even show duplicate (but > > internally different!) pairs when the raw i_ino/s_dev is used. > > How is it that you can dump the raw ino and s_dev if your not in > kernel code? If you look below my first paragraph, you'll see a list of places where the kernel publishes (maybe that's a better word?) ino/dev pairs by printing or otherwise copying raw ino/s_dev values into user accesible buffers. > For stat family system calls, if the file system defines the inode > operation getattr it will be used to fill the stat structure otherwise > the VFS will fill the stat structure and it will use inode->i_ino and > sb->s_dev as you say. My concern is that those pairs are sometimes not unique and do not line up with what statx(2) returns. We actually need the true inode / device as is returned by statx in those places. I go into much more detail in my original mail. > > Some examples where we dump raw ino/dev: > > > > - /proc/<pid>/maps. I've written about how this confuses lsof(8): > > https://marc.info/?l=linux-btrfs&m=130074451403261&w=2 > > > > - Unsurprisingly, many VFS tracepoints dump ino and/or dev. See > > trace/events/lock.h or trace/events/writeback.h for examples. > > > > - eventpoll also dumps the raw ino/dev pair via ep_show_fdinfo() > > > > - Audit records the raw ino/dev and passes them around. We do seem to > > have paths printed from audit as well, but if it's printed with the > > wrong ino/dev pair I believe my point still stands. > > > > > > This breaks software which expects these pairs to be unique, and can > > put the user in a situation where they might not be able to find an > > inode referenced from the kernel. What's even worse - depending on how > > ino is exported, they might even find the *wrong* inode. Thanks, --Mark
