pidfs: use maple tree
So far we've been using an idr to track pidfs inodes. For some time now
each struct pid has a unique 64bit value that is used as the inode
number on 64 bit. That unique inode couldn't be used for looking up a
specific struct pid though.
Now that we support file handles we need this ability while avoiding to
leak actual pid identifiers into userspace which can be problematic in
containers.
So far I had used an idr-based mechanism where the idr is used to
generate a 32 bit number and each time it wraps we increment an upper
bit value and generate a unique 64 bit value. The lower 32 bits are used
to lookup the pid.
I've been looking at the maple tree because it now has
mas_alloc_cyclic(). Since it uses unsigned long it would simplify the
64bit implementation and its dense node mode supposedly also helps to
mitigate fragmentation.
Signed-off-by: Christian Brauner <brauner@kernel.org>
2 files changed
