Re: [PATCH perf/core 6/6] tools lib bpf: Add bpf_object__pin()

["Wangnan (F)" <wangnan0@huawei.com>]

On 2017/1/19 7:57, Joe Stringer wrote:
> Add a new API to pin a BPF object to the filesystem. The user can
> specify a subdirectory under the BPF filesystem to pin these programs.
>
> For example, with the subdirectory 'foo', programs and maps are pinned:
> /sys/fs/bpf/foo/progs/PROG_NAME
> /sys/fs/bpf/foo/maps/MAP_NAME
>
> If the user has specified an alternative BPF filesystem mountpoint via
> /proc/mounts, that will be read and used instead.
>
> Signed-off-by: Joe Stringer <joe@ovn.org>
> ---
>   tools/lib/bpf/libbpf.c | 136 +++++++++++++++++++++++++++++++++++++++++++++++++
>   tools/lib/bpf/libbpf.h |   1 +
>   2 files changed, 137 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6b651c19870d..181dca0bdacb 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4,6 +4,7 @@
>    * Copyright (C) 2013-2015 Alexei Starovoitov <ast@kernel.org>
>    * Copyright (C) 2015 Wang Nan <wangnan0@huawei.com>
>    * Copyright (C) 2015 Huawei Inc.
> + * Copyright (C) 2016 Nicira, Inc.
>    *
>    * This program is free software; you can redistribute it and/or
>    * modify it under the terms of the GNU Lesser General Public
> @@ -31,7 +32,12 @@
>   #include <linux/err.h>
>   #include <linux/kernel.h>
>   #include <linux/bpf.h>
> +#include <linux/magic.h>
>   #include <linux/list.h>
> +#include <linux/limits.h>
> +#include <sys/mount.h>
> +#include <sys/stat.h>
> +#include <sys/vfs.h>
>   #include <libelf.h>
>   #include <gelf.h>
>   
> @@ -1231,6 +1237,136 @@ int bpf_object__load(struct bpf_object *obj)
>   	return err;
>   }
>   
> +#define stringize(x) #x
> +
> +static int mount_bpf(char *path)

We can use tools/lib/api/fs/fs.c to help us mounting filesystems.
Try not reinventing it.

> +{
> +	const char *mounts_fmt = "%*s %"stringize(PATH_MAX)"s %#"stringize(NAME_MAX)"s %*s\n";
> +	struct statfs st_fs;
> +	char type[NAME_MAX];
> +	int err = 0;
> +	FILE *fp;
> +
> +	/* Populate 'path'. */
> +	fp = fopen("/proc/mounts", "r");
> +	if (fp) {
> +		while (fscanf(fp, mounts_fmt, path, type) == 2) {
> +			if (!strcmp(type, "bpf"))
> +				break;
> +		}
> +		if (fclose(fp)) {
> +			err = -errno;
> +			pr_warning("failed to close /proc/mounts: %s\n",
> +				   strerror(errno));
> +		}
> +		if (strcmp(type, "bpf")) {
> +			err = -errno;
> +			pr_debug("failed to find bpf mount\n");
> +		}
> +	} else {
> +		err = -errno;
> +		pr_warning("cannot open /proc/mounts: %s\n", strerror(errno));
> +	}
> +	if (err) {
> +		pr_debug("using /sys/fs/bpf for BPF filesystem mountpoint\n");
> +		strcpy(path, "/sys/fs/bpf");
> +	}
> +
> +	if (!statfs(path, &st_fs) && st_fs.f_type == BPF_FS_MAGIC)
> +		return 0;
> +
> +	if (mount("bpf", path, "bpf", 0, NULL)) {
> +		pr_warning("failed to mount bpf: %s\n", strerror(errno));
> +		return -errno;
> +	}
> +
> +	return 0;
> +}
> +
> +static int make_dirs(const char *path, const char *subdir, char *buf,
> +		     size_t len)
> +{
> +	snprintf(buf, len, "%s/%s/", path, subdir);
> +	if (mkdir(buf, 0700) && errno != EEXIST) {
> +		pr_warning("failed to mkdir %s: %s\n", subdir, strerror(errno));
> +		return -errno;
> +	}
> +
> +	snprintf(buf, len, "%s/%s/maps/", path, subdir);
> +	if (mkdir(buf, 0700) && errno != EEXIST) {
> +		pr_warning("failed to mkdir map: %s\n", strerror(errno));
> +		return -errno;
> +	}
> +
> +	snprintf(buf, len, "%s/%s/progs/", path, subdir);
> +	if (mkdir(buf, 0700) && errno != EEXIST) {
> +		pr_warning("failed to mkdir prog: %s\n", strerror(errno));
> +		return -errno;
> +	}
> +
> +	return 0;
> +}
> +
> +int bpf_object__pin(struct bpf_object *obj, const char *subdir)
> +{

We must pin a whole object? I suggest we provide
bpf_program__pin and bpf_map__pin, and build bpf_object__pin
on top of them.

Thank you.

> +	const size_t len = 255;
> +	char path[PATH_MAX];
> +	char buf[len];
> +	size_t i, j;
> +	int err = 0;
> +
> +	if (!obj)
> +		return -ENOENT;
> +
> +	if (!obj->loaded) {
> +		pr_warning("object not yet loaded; load it first\n");
> +		return -ENOENT;
> +	}
> +
> +	err = mount_bpf(path);
> +	if (err)
> +		return err;
> +
> +	err = make_dirs(path, subdir, buf, len);
> +	if (err)
> +		return err;
> +
> +	for (i = 0; i < obj->nr_maps; i++) {
> +		struct bpf_map *map = &obj->maps[i];
> +
> +		snprintf(buf, len, "%s/%s/maps/%s", path, subdir,
> +			 bpf_map__name(map));
> +		if (bpf_obj_pin(map->fd, buf)) {
> +			err = -errno;
> +			pr_warning("failed to pin map: %s\n", strerror(errno));
> +			goto out;
> +		}
> +		pr_debug("Loaded map '%s' at '%s'\n", bpf_map__name(map), buf);
> +	}
> +
> +	if (obj->programs && obj->nr_programs) {
> +		for (i = 0; i < obj->nr_programs; i++) {
> +			struct bpf_program *prog = &obj->programs[i];
> +
> +			for (j = 0; j < prog->instances.nr; j++) {
> +				snprintf(buf, len, "%s/%s/progs/%s_%zu", path,
> +					 subdir, prog->section_name, j);
> +				if (bpf_obj_pin(prog->instances.fds[j], buf)) {
> +					err = -errno;
> +					pr_warning("failed to pin prog: %s\n",
> +						   strerror(errno));
> +					goto out;
> +				}
> +				pr_debug("Loaded prog '%s' at '%s'\n",
> +					 prog->section_name, buf);
> +			}
> +		}
> +	}
> +
> +out:
> +	return err;
> +}
> +
>   void bpf_object__close(struct bpf_object *obj)
>   {
>   	size_t i;
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 4014d1ba5e3d..920699a437be 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -65,6 +65,7 @@ struct bpf_object *bpf_object__open(const char *path);
>   struct bpf_object *bpf_object__open_buffer(void *obj_buf,
>   					   size_t obj_buf_sz,
>   					   const char *name);
> +int bpf_object__pin(struct bpf_object *object, const char *subdir);
>   void bpf_object__close(struct bpf_object *object);
>   
>   /* Load/unload object into/from kernel */