This introduces RECURSE_DIR_UNLINK + RECURSE_DIR_UNLINK_GRACEFUL as new
return values for recurse_dir() callbacks. If either is returned the
inode currently processed will be removed and iteration continues with
the next item.
This is useful to have in the recurse_dir() mechanism itself (rather
than implement in the callback itself), due to ordering: we want to pin
the inodes via an fd while calling the callbacks, but we have to close
it before removal of the inodes. By moving this into the recurse_dir()
infra, we can implement this easily.
Let's not leak details from src/shared and src/libsystemd into
src/basic, even though you can't actually do anything useful with
just forward declarations from src/shared.
The sd-forward.h header is put in src/libsystemd/sd-common as we
don't have a directory for shared internal headers for libsystemd
yet.
Let's also rename forward.h to basic-forward.h to keep things
self-explanatory.
So far recurse_dir() will call the callback whenever we enter a
directory, and then pass the struct dirent for that directory, and an fd
for the directory the dirent is part of (i.e. the parent of the
directory we call things for). For the top-level dir the function is
invoked for we will not call the callback however, because we have no
dirent for that, and not fd for the directory the top-level dir is part
of. Let's add a flag to call it anyway, and in that case pass a NULL
dirent and -1 as directory fd.
This is useful when we want to treat the top-level dir the same as any
dir further down.
This is done opt-in since the callback must be ablet to handle a NULL
dirent and a -1 directory fd.
We already have a similar loop twice, let's make it easier to read via
an iteration macro.
(The new macro is a bit more careful even, as it verifies the full
dirent fits into the remaining buffer when returning it)
Let's use the underlying Linux API directly, instead of
opendir()/readdir(). This makes it possible for us to do a single memory
allocation for all directory entries in common cases, instead of one for
each entry.
libc nftw() shows its age a bit, let's replace it with a more moden
infra that is built around openat(), O_PATH, statx(). This makes the
interface less prone to races and cleans up the API a bit adding
substantially more functionality.
Lennart Poettering
Daan De Meyer
Mike Yuan