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Tue, 06 May 2025 14:38:53 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250505-vmlinux-mmap-v3-0-5d53afa060e8@isovalent.com> <20250505-vmlinux-mmap-v3-3-5d53afa060e8@isovalent.com> In-Reply-To: <20250505-vmlinux-mmap-v3-3-5d53afa060e8@isovalent.com> From: Andrii Nakryiko Date: Tue, 6 May 2025 14:38:41 -0700 X-Gm-Features: ATxdqUGGCDGg2tnfgumvbm6h04EAY8VmSj63XahGKHqk0wu1txc2sMopPtImsZ0 Message-ID: Subject: Re: [PATCH bpf-next v3 3/3] libbpf: Use mmap to parse vmlinux BTF from sysfs To: Lorenz Bauer Cc: Arnd Bergmann , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Mykola Lysenko , Shuah Khan , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, May 5, 2025 at 11:39=E2=80=AFAM Lorenz Bauer wr= ote: > > Teach libbpf to use mmap when parsing vmlinux BTF from /sys. We don't > apply this to fall-back paths on the regular file system because there > is no way to ensure that modifications underlying the MAP_PRIVATE > mapping are not visible to the process. > > Signed-off-by: Lorenz Bauer > --- > tools/lib/bpf/btf.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++-= ------ > 1 file changed, 72 insertions(+), 11 deletions(-) > [...] > @@ -1030,7 +1045,7 @@ struct btf *btf__new_empty_split(struct btf *base_b= tf) > return libbpf_ptr(btf_new_empty(base_btf)); > } > > -static struct btf *btf_new(const void *data, __u32 size, struct btf *bas= e_btf) > +static struct btf *btf_new_no_copy(void *data, __u32 size, struct btf *b= ase_btf) > { > struct btf *btf; > int err; > @@ -1050,12 +1065,7 @@ static struct btf *btf_new(const void *data, __u32= size, struct btf *base_btf) > btf->start_str_off =3D base_btf->hdr->str_len; > } > > - btf->raw_data =3D malloc(size); > - if (!btf->raw_data) { > - err =3D -ENOMEM; > - goto done; > - } > - memcpy(btf->raw_data, data, size); > + btf->raw_data =3D data; > btf->raw_size =3D size; > > btf->hdr =3D btf->raw_data; > @@ -1081,6 +1091,24 @@ static struct btf *btf_new(const void *data, __u32= size, struct btf *base_btf) > return btf; > } > > +static struct btf *btf_new(const void *data, __u32 size, struct btf *bas= e_btf) btf_new() is internal, so I'd extend existing btf_new() with `bool is_mmap` and not add btf_new_no_copy(), I think it's simpler. Eventually we can turn is_mmap into some sort of flags, if we need more tuning of data ownership behavior > +{ > + struct btf *btf; > + void *raw_data; > + > + raw_data =3D malloc(size); > + if (!raw_data) > + return ERR_PTR(-ENOMEM); > + > + memcpy(raw_data, data, size); > + > + btf =3D btf_new_no_copy(raw_data, size, base_btf); > + if (IS_ERR(btf)) > + free(raw_data); > + > + return btf; > +} > + > struct btf *btf__new(const void *data, __u32 size) > { > return libbpf_ptr(btf_new(data, size, NULL)); > @@ -1354,6 +1382,37 @@ struct btf *btf__parse_raw_split(const char *path,= struct btf *base_btf) > return libbpf_ptr(btf_parse_raw(path, base_btf)); > } > > +static struct btf *btf_parse_raw_mmap(const char *path, struct btf *base= _btf) > +{ > + struct stat st; > + void *data; > + struct btf *btf; > + int fd; > + > + fd =3D open(path, O_RDONLY); > + if (fd < 0) > + return libbpf_err_ptr(-errno); > + > + if (fstat(fd, &st) < 0) { > + close(fd); close() can clobber errno, so save `err =3D -errno` before it > + return libbpf_err_ptr(-errno); > + } > + > + data =3D mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0); > + close(fd); same, errno clobbering danger > + > + if (data =3D=3D MAP_FAILED) > + return NULL; > + > + btf =3D btf_new_no_copy(data, st.st_size, base_btf); > + if (!btf) btf_new_no_copy() is returning ERR_PTR() on error, no? pw-bot: cr > + munmap(data, st.st_size); > + else > + btf->raw_data_is_mmap =3D true; > + > + return btf; > +} > + > static struct btf *btf_parse(const char *path, struct btf *base_btf, str= uct btf_ext **btf_ext) > { > struct btf *btf; > @@ -1659,8 +1718,7 @@ struct btf *btf__load_from_kernel_by_id(__u32 id) > static void btf_invalidate_raw_data(struct btf *btf) > { > if (btf->raw_data) { > - free(btf->raw_data); > - btf->raw_data =3D NULL; > + btf_free_raw_data(btf); > } > if (btf->raw_data_swapped) { > free(btf->raw_data_swapped); > @@ -5290,7 +5348,10 @@ struct btf *btf__load_vmlinux_btf(void) > pr_warn("kernel BTF is missing at '%s', was CONFIG_DEBUG_= INFO_BTF enabled?\n", > sysfs_btf_path); > } else { > - btf =3D btf__parse(sysfs_btf_path, NULL); > + btf =3D btf_parse_raw_mmap(sysfs_btf_path, NULL); > + if (IS_ERR_OR_NULL(btf)) > + btf =3D btf__parse(sysfs_btf_path, NULL); > + > if (!btf) { > err =3D -errno; > pr_warn("failed to read kernel BTF from '%s': %s\= n", > > -- > 2.49.0 >