On Mon, 25.05.15 21:06, Martin Pitt (martin.p...@ubuntu.com) wrote:
Hello all,
in 220, path_is_mount_point() now always fails with -20 ENOTDIR when
calling it on files. This is problematic as it's perfectly valid to
have bind-mounted files; in fact, systemd's machine_id_setup() itself
creates a /run/machine-id → /etc/machine-id bind mount if /etc is
read-only at that time (and systemd-machine-id-commit will write it
once root fs becomes writable).
This was first introduced here:
http://cgit.freedesktop.org/systemd/systemd/commit/?id=27cc6f166
path-util: fix path_is_mount_point() for symlinks
which added O_DIRECTORY, so that openat() fails with the above error.
It also replaced path_get_parent() (which works fine for files) with
name_to_handle_at(fd, .., ...) which only works for directories.
In fd_is_mount_point() we obviously don't have access to the file name
any more, and presumably we do want to keep it for efficiently
implementing the rm-rf: never cross mount points commit f25afeb.
Since all possible checks in fd_is_mount_point() rely on *at(, ..)
which doesn't work for files, one solution that I see
is to add a fallback path_is_mountpoint() if fd_is_mount_point() fails
with ENOTDIR; in that case, should we implement all fallbacks again
(lots of duplicated code), or just one (st_dev comparison, which seems
the most widely supported one)?
Alternatively we could pass a parent_path to fd_is_mount_point(),
compute that in path_is_mountpoint(), and don't specify one (or maybe
we even can specify it easily, I didn't check) in rm_rf_children() as
file bind mounts don't seem relevant there. This would be simpler, but
it would technically be an API break (unless we want to add
fd_is_mount_point_with_parent).
Not an API break. Only calls prefixed with sd_ are API, we never
export any others.
But yeah, path_is_mount_point() should be reworked to operate like
openat() and similar calls, i.e. taking an fd to a dir, plus a
filename below that dir, instead of directly and only an fd to the
file below that dir.
Lennart
--
Lennart Poettering, Red Hat
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