From: Andrii Nakryiko <andrii.nakryiko@gmail.com> To: "Toke Høiland-Jørgensen" <toke@redhat.com> Cc: Daniel Borkmann <daniel@iogearbox.net>, Alexei Starovoitov <ast@kernel.org>, Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>, Jesper Dangaard Brouer <brouer@redhat.com>, David Miller <davem@davemloft.net>, Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org> Subject: Re: [PATCH bpf-next 3/3] libbpf: Add pin option to automount BPF filesystem before pinning Date: Tue, 22 Oct 2019 21:58:41 -0700 [thread overview] Message-ID: <CAEf4Bzap3oMPnGJQAsoV-g77ux0FdELiJpvpxn9_zadVnHYdSA@mail.gmail.com> (raw) In-Reply-To: <8736fkob4g.fsf@toke.dk> On Tue, Oct 22, 2019 at 12:04 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote: > > Andrii Nakryiko <andrii.nakryiko@gmail.com> writes: > > > On Tue, Oct 22, 2019 at 9:08 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote: > >> > >> From: Toke Høiland-Jørgensen <toke@redhat.com> > >> > >> While the current map pinning functions will check whether the pin path is > >> contained on a BPF filesystem, it does not offer any options to mount the > >> file system if it doesn't exist. Since we now have pinning options, add a > >> new one to automount a BPF filesystem at the pinning path if that is not > > > > Next thing we'll be adding extra options to mount BPF FS... Can we > > leave the task of auto-mounting BPF FS to tools/applications? > > Well, there was a reason I put this into a separate patch: I wasn't sure > it really fit here. My reasoning is the following: If we end up with a > default auto-pinning that works really well, people are going to just > use that. And end up really confused when bpffs is not mounted. And it > seems kinda silly to make every application re-implement the same mount > check and logic. > > Or to put it another way: If we agree that the reasonable default thing > is to just pin things in /sys/fs/bpf, let's make it as easy as possible > for applications to do that right. > This reminds me the setrlimit() issue, though. And we decided that library shouldn't be manipulating global resources on behalf of users. I think this is a similar one. > >> already pointing at a bpffs. > >> > >> The mounting logic itself is copied from the iproute2 BPF helper functions. > >> > >> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> > >> --- > >> tools/lib/bpf/libbpf.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ > >> tools/lib/bpf/libbpf.h | 5 ++++- > >> 2 files changed, 51 insertions(+), 1 deletion(-) > >> > >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > >> index aea3916de341..f527224bb211 100644 > >> --- a/tools/lib/bpf/libbpf.c > >> +++ b/tools/lib/bpf/libbpf.c > >> @@ -37,6 +37,7 @@ > >> #include <sys/epoll.h> > >> #include <sys/ioctl.h> > >> #include <sys/mman.h> > >> +#include <sys/mount.h> > >> #include <sys/stat.h> > >> #include <sys/types.h> > >> #include <sys/vfs.h> > >> @@ -4072,6 +4073,35 @@ int bpf_map__unpin(struct bpf_map *map, const char *path) > >> return 0; > >> } > >> > >> +static int mount_bpf_fs(const char *target) > >> +{ > >> + bool bind_done = false; > >> + > >> + while (mount("", target, "none", MS_PRIVATE | MS_REC, NULL)) { > > > > what does this loop do? we need some comments explaining what's going > > on here > > Well, as it says in the commit message I stole this from iproute2. I > think the "--make-private, --bind" dance is there to make sure we don't > mess up some other mount points at this path. Which seems like a good > idea, and one of those things that most people probably won't think > about when just writing an application that wants to mount the fs; which > is another reason to put this into libbpf :) I think this is exactly a reason to not do this and rely on applications to know and set up their environment properly. All these races, accidentally stomping on someone else's FS, etc, that sounds like a really good excuse to not do this in libbpf. Definitely not until we get a real experience, driven by production use cases, on how to go about that correctly. It might be added as a helper, but I think application has to call it explicitly. > > >> + if (errno != EINVAL || bind_done) { > >> + pr_warning("mount --make-private %s failed: %s\n", > >> + target, strerror(errno)); > >> + return -1; > >> + } > >> + > >> + if (mount(target, target, "none", MS_BIND, NULL)) { > >> + pr_warning("mount --bind %s %s failed: %s\n", > >> + target, target, strerror(errno)); > >> + return -1; > >> + } > >> + > >> + bind_done = true; > >> + } > >> + > >> + if (mount("bpf", target, "bpf", 0, "mode=0700")) { > >> + fprintf(stderr, "mount -t bpf bpf %s failed: %s\n", > >> + target, strerror(errno)); > >> + return -1; > >> + } > >> + > >> + return 0; > >> +} > >> + > >> static int get_pin_path(char *buf, size_t buf_len, > >> struct bpf_map *map, struct bpf_object_pin_opts *opts, > >> bool mkdir) > >> @@ -4102,6 +4132,23 @@ static int get_pin_path(char *buf, size_t buf_len, > > > > Nothing in `get_pin_path` indicates that it's going to do an entire FS > > mount, please split this out of get_pin_path. > > Regardless of the arguments above, that is certainly a fair point ;) > > -Toke
next prev parent reply other threads:[~2019-10-23 4:58 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-22 15:04 [PATCH bpf-next 0/3] libbpf: Support pinning of maps using 'pinning' BTF attribute Toke Høiland-Jørgensen 2019-10-22 15:04 ` [PATCH bpf-next 1/3] libbpf: Store map pin path in struct bpf_map Toke Høiland-Jørgensen 2019-10-22 17:37 ` Andrii Nakryiko 2019-10-22 18:13 ` Toke Høiland-Jørgensen 2019-10-22 18:23 ` Andrii Nakryiko 2019-10-22 18:45 ` Toke Høiland-Jørgensen 2019-10-22 18:49 ` Andrii Nakryiko 2019-10-22 19:06 ` Toke Høiland-Jørgensen 2019-10-23 4:43 ` Andrii Nakryiko 2019-10-22 15:04 ` [PATCH bpf-next 2/3] libbpf: Support configurable pinning of maps from BTF annotations Toke Høiland-Jørgensen 2019-10-22 18:20 ` Andrii Nakryiko 2019-10-22 18:57 ` Toke Høiland-Jørgensen 2019-10-23 4:40 ` Andrii Nakryiko 2019-10-23 8:53 ` Toke Høiland-Jørgensen 2019-10-23 12:30 ` Daniel Borkmann 2019-10-23 13:05 ` Toke Høiland-Jørgensen 2019-10-22 15:04 ` [PATCH bpf-next 3/3] libbpf: Add pin option to automount BPF filesystem before pinning Toke Høiland-Jørgensen 2019-10-22 18:28 ` Andrii Nakryiko 2019-10-22 19:04 ` Toke Høiland-Jørgensen 2019-10-23 4:58 ` Andrii Nakryiko [this message] 2019-10-23 8:58 ` Toke Høiland-Jørgensen
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