On Tue, Oct 22, 2019 at 11:45 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes:
>
> > On Tue, Oct 22, 2019 at 11:13 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
> >>
> >> Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes:
> >>
> >> > On Tue, Oct 22, 2019 at 9:08 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
> >> >>
> >> >> From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> >> >>
> >> >> When pinning a map, store the pin path in struct bpf_map so it can be
> >> >> re-used later for un-pinning. This simplifies the later addition of per-map
> >> >> pin paths.
> >> >>
> >> >> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> >> >> ---
> >> >> tools/lib/bpf/libbpf.c | 19 ++++++++++---------
> >> >> 1 file changed, 10 insertions(+), 9 deletions(-)
> >> >>
> >> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> >> >> index cccfd9355134..b4fdd8ee3bbd 100644
> >> >> --- a/tools/lib/bpf/libbpf.c
> >> >> +++ b/tools/lib/bpf/libbpf.c
> >> >> @@ -226,6 +226,7 @@ struct bpf_map {
> >> >> void *priv;
> >> >> bpf_map_clear_priv_t clear_priv;
> >> >> enum libbpf_map_type libbpf_type;
> >> >> + char *pin_path;
> >> >> };
> >> >>
> >> >> struct bpf_secdata {
> >> >> @@ -1929,6 +1930,7 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
> >> >> if (err)
> >> >> goto err_close_new_fd;
> >> >> free(map->name);
> >> >> + zfree(&map->pin_path);
> >> >>
> >> >
> >> > While you are touching this function, can you please also fix error
> >> > handling in it? We should store -errno locally on error, before we
> >> > call close() which might change errno.
> >>
> >> Didn't actually look much at the surrounding function, TBH. I do expect
> >> that I will need to go poke into this for the follow-on "automatic reuse
> >> of pinned maps" series anyway. But sure, I can do a bit of cleanup in a
> >> standalone patch first :)
> >>
> >> >> map->fd = new_fd;
> >> >> map->name = new_name;
> >> >> @@ -4022,6 +4024,7 @@ int bpf_map__pin(struct bpf_map *map, const char *path)
> >> >> return -errno;
> >> >> }
> >> >>
> >> >> + map->pin_path = strdup(path);
> >> >
> >> > if (!map->pin_path) {
> >> > err = -errno;
> >> > goto err_close_new_fd;
> >> > }
> >>
> >> Right.
> >>
> >> >> pr_debug("pinned map '%s'\n", path);
> >> >>
> >> >> return 0;
> >> >> @@ -4031,6 +4034,9 @@ int bpf_map__unpin(struct bpf_map *map, const char *path)
> >> >> {
> >> >> int err;
> >> >>
> >> >> + if (!path)
> >> >> + path = map->pin_path;
> >> >
> >> > This semantics is kind of weird. Given we now remember pin_path,
> >> > should we instead check that user-provided path is actually correct
> >> > and matches what we stored? Alternatively, bpf_map__unpin() w/o path
> >> > argument looks like a cleaner API.
> >>
> >> Yeah, I guess the function without a path argument would make the most
> >> sense. However, we can't really change the API of bpf_map__unpin()
> >> (unless you're proposing a symbol-versioned new version?). Dunno if it's
> >> worth it to include a new, somewhat oddly-named, function to achieve
> >> this? For the internal libbpf uses at least it's easy enough for the
> >> caller to just go bpf_map__unpin(map, map->pin_path), so I could also
> >> just drop this change? WDYT?
> >
> > I'd probably do strcmp(map->pin_path, path), if path is specified.
> > This will support existing use cases, will allow NULL if we don't want
> > to bother remembering pin_path, will prevent weird use case of pinning
> > to one path, but unpinning another one.
>
> So something like
>
> if (path && map->pin_path && strcmp(path, map->pin_path))
can we unpin not pinned map? sounds like an error condition?
so:
if (!map->pin_path)
return -EWHATAREYOUDOING;
if (path && strcmp(path, map->pin_path))
return -EHUH;
path = map->pin_path; /* or just use map->ping_path explicitly */
... proceed ...
> return -EINVAL
> else if (!path)
> path = map->pin_path;
>
> ?
>
> > Ideally, all this pinning will just be done declaratively and will
> > happen automatically, so users won't even have to know about this API
> > :)
>
> Yeah, that's where I'm hoping to get to. But, well, the pin/unpin
> functions already exist so we do need to keep them working...
>
> -Toke
