| Message ID | 20220521075736.1225397-1-zenczykowski@gmail.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF |
| Headers | show |
| Series | [bpf-next] bpf: print a little more info about maps via cat /sys/fs/bpf/pinned_name | expand |
On Sat, May 21, 2022 at 12:57 AM Maciej Żenczykowski <zenczykowski@gmail.com> wrote: > > From: Maciej Żenczykowski <maze@google.com> > > While this information can be fetched via bpftool, > the cli tool itself isn't always available on more limited systems. > > From the information printed particularly the 'id' is useful since > when combined with /proc/pid/fd/X and /proc/pid/fdinfo/X it allows > tracking down which bpf maps a process has open (which can be > useful for tracking down fd leaks). > > Signed-off-by: Maciej Żenczykowski <maze@google.com> > --- > kernel/bpf/inode.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c > index 4f841e16779e..784266e258fe 100644 > --- a/kernel/bpf/inode.c > +++ b/kernel/bpf/inode.c > @@ -257,6 +257,9 @@ static int map_seq_show(struct seq_file *m, void *v) > if (unlikely(v == SEQ_START_TOKEN)) { > seq_puts(m, "# WARNING!! The output is for debug purpose only\n"); > seq_puts(m, "# WARNING!! The output format will change\n"); > + seq_printf(m, "# type: %d, key_size: %d, value_size: %d, max_entries: %d, id: %d\n", > + map->map_type, map->key_size, map->value_size, map->max_entries, > + map->id); Maybe use cat /sys/fs/bpf/maps.debug instead? It prints map id.
On Mon, May 23, 2022 at 12:32 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: > > On Sat, May 21, 2022 at 12:57 AM Maciej Żenczykowski > <zenczykowski@gmail.com> wrote: > > > > From: Maciej Żenczykowski <maze@google.com> > > > > While this information can be fetched via bpftool, > > the cli tool itself isn't always available on more limited systems. > > > > From the information printed particularly the 'id' is useful since > > when combined with /proc/pid/fd/X and /proc/pid/fdinfo/X it allows > > tracking down which bpf maps a process has open (which can be > > useful for tracking down fd leaks). > > > > Signed-off-by: Maciej Żenczykowski <maze@google.com> > > --- > > kernel/bpf/inode.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c > > index 4f841e16779e..784266e258fe 100644 > > --- a/kernel/bpf/inode.c > > +++ b/kernel/bpf/inode.c > > @@ -257,6 +257,9 @@ static int map_seq_show(struct seq_file *m, void *v) > > if (unlikely(v == SEQ_START_TOKEN)) { > > seq_puts(m, "# WARNING!! The output is for debug purpose only\n"); > > seq_puts(m, "# WARNING!! The output format will change\n"); > > + seq_printf(m, "# type: %d, key_size: %d, value_size: %d, max_entries: %d, id: %d\n", > > + map->map_type, map->key_size, map->value_size, map->max_entries, > > + map->id); > > Maybe use cat /sys/fs/bpf/maps.debug instead? > It prints map id. Is this something that was very recently added? I'm not seeing it on my 5.16 machine with bpffs mounted at /sys/fs/bpf.
On Mon, May 23, 2022 at 1:14 PM Maciej Żenczykowski <zenczykowski@gmail.com> wrote: > > On Mon, May 23, 2022 at 12:32 PM Alexei Starovoitov > <alexei.starovoitov@gmail.com> wrote: > > > > On Sat, May 21, 2022 at 12:57 AM Maciej Żenczykowski > > <zenczykowski@gmail.com> wrote: > > > > > > From: Maciej Żenczykowski <maze@google.com> > > > > > > While this information can be fetched via bpftool, > > > the cli tool itself isn't always available on more limited systems. > > > > > > From the information printed particularly the 'id' is useful since > > > when combined with /proc/pid/fd/X and /proc/pid/fdinfo/X it allows > > > tracking down which bpf maps a process has open (which can be > > > useful for tracking down fd leaks). > > > > > > Signed-off-by: Maciej Żenczykowski <maze@google.com> > > > --- > > > kernel/bpf/inode.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c > > > index 4f841e16779e..784266e258fe 100644 > > > --- a/kernel/bpf/inode.c > > > +++ b/kernel/bpf/inode.c > > > @@ -257,6 +257,9 @@ static int map_seq_show(struct seq_file *m, void *v) > > > if (unlikely(v == SEQ_START_TOKEN)) { > > > seq_puts(m, "# WARNING!! The output is for debug purpose only\n"); > > > seq_puts(m, "# WARNING!! The output format will change\n"); > > > + seq_printf(m, "# type: %d, key_size: %d, value_size: %d, max_entries: %d, id: %d\n", > > > + map->map_type, map->key_size, map->value_size, map->max_entries, > > > + map->id); > > > > Maybe use cat /sys/fs/bpf/maps.debug instead? > > It prints map id. > > Is this something that was very recently added? > I'm not seeing it on my 5.16 machine with bpffs mounted at /sys/fs/bpf. It was there since 2020. Make sure you have CONFIG_BPF_PRELOAD.
On Mon, May 23, 2022 at 1:21 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: > > On Mon, May 23, 2022 at 1:14 PM Maciej Żenczykowski > <zenczykowski@gmail.com> wrote: > > > > On Mon, May 23, 2022 at 12:32 PM Alexei Starovoitov > > <alexei.starovoitov@gmail.com> wrote: > > > > > > On Sat, May 21, 2022 at 12:57 AM Maciej Żenczykowski > > > <zenczykowski@gmail.com> wrote: > > > > > > > > From: Maciej Żenczykowski <maze@google.com> > > > > > > > > While this information can be fetched via bpftool, > > > > the cli tool itself isn't always available on more limited systems. > > > > > > > > From the information printed particularly the 'id' is useful since > > > > when combined with /proc/pid/fd/X and /proc/pid/fdinfo/X it allows > > > > tracking down which bpf maps a process has open (which can be > > > > useful for tracking down fd leaks). > > > > > > > > Signed-off-by: Maciej Żenczykowski <maze@google.com> > > > > --- > > > > kernel/bpf/inode.c | 3 +++ > > > > 1 file changed, 3 insertions(+) > > > > > > > > diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c > > > > index 4f841e16779e..784266e258fe 100644 > > > > --- a/kernel/bpf/inode.c > > > > +++ b/kernel/bpf/inode.c > > > > @@ -257,6 +257,9 @@ static int map_seq_show(struct seq_file *m, void *v) > > > > if (unlikely(v == SEQ_START_TOKEN)) { > > > > seq_puts(m, "# WARNING!! The output is for debug purpose only\n"); > > > > seq_puts(m, "# WARNING!! The output format will change\n"); > > > > + seq_printf(m, "# type: %d, key_size: %d, value_size: %d, max_entries: %d, id: %d\n", > > > > + map->map_type, map->key_size, map->value_size, map->max_entries, > > > > + map->id); > > > > > > Maybe use cat /sys/fs/bpf/maps.debug instead? > > > It prints map id. > > > > Is this something that was very recently added? > > I'm not seeing it on my 5.16 machine with bpffs mounted at /sys/fs/bpf. > > It was there since 2020. > Make sure you have CONFIG_BPF_PRELOAD. Hmm. This seems very annoying to use in practice. * it seems to default to disabled, and as such is disabled on: - my Debian laptop and desktop (well google's corp Linux distro, but it should be close enough to Debian here) - my latest Fedora 36 Desktop and VMs - our production (server) kernels - all current Android Common Kernel / Generic Kernel Image / Pixel kernel trees - Android UML test image kernel build scripts * enabling it on our server kernels results in a compilation failure (probably some missing backports, they're backported up the wazoo) * enabling it on ACK 5.10 tree results in a very different build failure * enabling it on ACK 5.15 successfully builds, but doesn't seem to work: # uname -r 5.15.41-04342-g39bba8f6b9fe # zcat /proc/config.gz | egrep BPF_PRELOAD CONFIG_BPF_PRELOAD=y CONFIG_BPF_PRELOAD_UMD=y # cat /proc/mounts | egrep sys none /sys sysfs rw,relatime 0 0 none /sys/fs/bpf bpf rw,relatime 0 0 # cd /sys/fs/bpf root@uml-x86-64:/sys/fs/bpf# ls -al total 0 drwxrwxrwt 2 root root 0 May 25 15:13 . drwxr-xr-x 6 root root 0 May 25 15:13 .. Perhaps a limitation of UML, or something funky in the build process, or the files don't show up until maps/progs are pinned? Hard to say - this is after running our bpf (python) test suite (though it might not use pinned maps/programs)... * finally.. I think it increases kernel size by a lot since I see: 120K ./kernel/bpf/preload/bpf_preload_kern.o and in a different tree: 232K ./kernel/bpf/preload/bpf_preload.ko I did get it to work by building a net next tree with the option manually enabled and installing it on some dev servers. Those by default have some pinned progs/maps, and I do see the debug files. When it works it's really nice... but I don't think I'm willing to pay the complexity/memory costs.
On Wed, May 25, 2022 at 9:14 AM Maciej Żenczykowski <zenczykowski@gmail.com> wrote: > > When it works it's really nice... Load your own bpf map iterator program and pin anywhere in bpffs under name of choice and your own access permissions. See selftests/bpf/progs/bpf_iter_bpf_map.c
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c index 4f841e16779e..784266e258fe 100644 --- a/kernel/bpf/inode.c +++ b/kernel/bpf/inode.c @@ -257,6 +257,9 @@ static int map_seq_show(struct seq_file *m, void *v) if (unlikely(v == SEQ_START_TOKEN)) { seq_puts(m, "# WARNING!! The output is for debug purpose only\n"); seq_puts(m, "# WARNING!! The output format will change\n"); + seq_printf(m, "# type: %d, key_size: %d, value_size: %d, max_entries: %d, id: %d\n", + map->map_type, map->key_size, map->value_size, map->max_entries, + map->id); } else { map->ops->map_seq_show_elem(map, key, m); }