[PATCH bpf-next v2] bpftool: use only nftw for file tree parsing

[PATCH bpf-next v2] bpftool: use only nftw for file tree parsing

[Tony Ambardar]

The bpftool sources include code to walk file trees, but use multiple
frameworks to do so: nftw and fts. While nftw conforms to POSIX/SUSv3 and
is widely available, fts is not conformant and less common, especially on
non-glibc systems. The inconsistent framework usage hampers maintenance
and portability of bpftool, in particular for embedded systems.

Standardize code usage by rewriting one fts-based function to use nftw.
Clean up related function warnings by using "const char *" arguments and
fixing an unsafe call to dirname().

These changes help in building bpftool against musl for OpenWrt.

Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
---

V2:
* use _GNU_SOURCE to pull in getpagesize(), getline(), nftw() definitions
* use "const char *" in open_obj_pinned() and open_obj_pinned_any()
* make dirname() safely act on a string copy

---
 tools/bpf/bpftool/common.c | 129 +++++++++++++++++++++----------------
 tools/bpf/bpftool/main.h   |   4 +-
 2 files changed, 76 insertions(+), 57 deletions(-)

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index 29f4e7611ae8..7c2e52fc5784 100644
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -1,10 +1,11 @@
 // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 /* Copyright (C) 2017-2018 Netronome Systems, Inc. */
 
+#define _GNU_SOURCE
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <fts.h>
+#include <ftw.h>
 #include <libgen.h>
 #include <mntent.h>
 #include <stdbool.h>
@@ -160,24 +161,36 @@ int mount_tracefs(const char *target)
 	return err;
 }
 
-int open_obj_pinned(char *path, bool quiet)
+int open_obj_pinned(const char *path, bool quiet)
 {
-	int fd;
+	char *pname;
+	int fd = -1;
+
+	pname = strdup(path);
+	if (pname == NULL) {
+		if (!quiet)
+			p_err("bpf obj get (%s): %s", path, strerror(errno));
+		goto out_ret;
+	}
+
 
-	fd = bpf_obj_get(path);
+	fd = bpf_obj_get(pname);
 	if (fd < 0) {
 		if (!quiet)
-			p_err("bpf obj get (%s): %s", path,
-			      errno == EACCES && !is_bpffs(dirname(path)) ?
+			p_err("bpf obj get (%s): %s", pname,
+			      errno == EACCES && !is_bpffs(dirname(pname)) ?
 			    "directory not in bpf file system (bpffs)" :
 			    strerror(errno));
-		return -1;
+		goto out_free;
 	}
 
+out_free:
+	free(pname);
+out_ret:
 	return fd;
 }
 
-int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type)
+int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type)
 {
 	enum bpf_obj_type type;
 	int fd;
@@ -367,68 +380,74 @@ void print_hex_data_json(uint8_t *data, size_t len)
 	jsonw_end_array(json_wtr);
 }
 
-int build_pinned_obj_table(struct pinned_obj_table *tab,
-			   enum bpf_obj_type type)
+static struct pinned_obj_table *build_fn_table; /* params for nftw cb*/
+static enum bpf_obj_type build_fn_type;
+
+static int do_build_table_cb(const char *fpath, const struct stat *sb,
+			    int typeflag, struct FTW *ftwbuf)
 {
 	struct bpf_prog_info pinned_info = {};
 	struct pinned_obj *obj_node = NULL;
 	__u32 len = sizeof(pinned_info);
-	struct mntent *mntent = NULL;
 	enum bpf_obj_type objtype;
+	int fd, err = 0;
+
+	if (typeflag != FTW_F)
+		goto out_ret;
+	fd = open_obj_pinned(fpath, true);
+	if (fd < 0)
+		goto out_ret;
+
+	objtype = get_fd_type(fd);
+	if (objtype != build_fn_type)
+		goto out_close;
+
+	memset(&pinned_info, 0, sizeof(pinned_info));
+	if (bpf_obj_get_info_by_fd(fd, &pinned_info, &len)) {
+		p_err("can't get obj info: %s", strerror(errno));
+		goto out_close;
+	}
+
+	obj_node = malloc(sizeof(*obj_node));
+	if (!obj_node) {
+		p_err("mem alloc failed");
+		err = -1;
+		goto out_close;
+	}
+
+	memset(obj_node, 0, sizeof(*obj_node));
+	obj_node->id = pinned_info.id;
+	obj_node->path = strdup(fpath);
+	hash_add(build_fn_table->table, &obj_node->hash, obj_node->id);
+
+out_close:
+	close(fd);
+out_ret:
+	return err;
+}
+
+int build_pinned_obj_table(struct pinned_obj_table *tab,
+			   enum bpf_obj_type type)
+{
+	struct mntent *mntent = NULL;
 	FILE *mntfile = NULL;
-	FTSENT *ftse = NULL;
-	FTS *fts = NULL;
-	int fd, err;
+	int flags = FTW_PHYS;
+	int nopenfd = 16;
 
 	mntfile = setmntent("/proc/mounts", "r");
 	if (!mntfile)
 		return -1;
 
+	build_fn_table = tab;
+	build_fn_type = type;
+
 	while ((mntent = getmntent(mntfile))) {
-		char *path[] = { mntent->mnt_dir, NULL };
+		char *path = mntent->mnt_dir;
 
 		if (strncmp(mntent->mnt_type, "bpf", 3) != 0)
 			continue;
-
-		fts = fts_open(path, 0, NULL);
-		if (!fts)
-			continue;
-
-		while ((ftse = fts_read(fts))) {
-			if (!(ftse->fts_info & FTS_F))
-				continue;
-			fd = open_obj_pinned(ftse->fts_path, true);
-			if (fd < 0)
-				continue;
-
-			objtype = get_fd_type(fd);
-			if (objtype != type) {
-				close(fd);
-				continue;
-			}
-			memset(&pinned_info, 0, sizeof(pinned_info));
-			err = bpf_obj_get_info_by_fd(fd, &pinned_info, &len);
-			if (err) {
-				close(fd);
-				continue;
-			}
-
-			obj_node = malloc(sizeof(*obj_node));
-			if (!obj_node) {
-				close(fd);
-				fts_close(fts);
-				fclose(mntfile);
-				return -1;
-			}
-
-			memset(obj_node, 0, sizeof(*obj_node));
-			obj_node->id = pinned_info.id;
-			obj_node->path = strdup(ftse->fts_path);
-			hash_add(tab->table, &obj_node->hash, obj_node->id);
-
-			close(fd);
-		}
-		fts_close(fts);
+		if (nftw(path, do_build_table_cb, nopenfd, flags) == -1)
+			break;
 	}
 	fclose(mntfile);
 	return 0;
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 78d34e860713..e3a79b5a9960 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -152,8 +152,8 @@ int cmd_select(const struct cmd *cmds, int argc, char **argv,
 int get_fd_type(int fd);
 const char *get_fd_type_name(enum bpf_obj_type type);
 char *get_fdinfo(int fd, const char *key);
-int open_obj_pinned(char *path, bool quiet);
-int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type);
+int open_obj_pinned(const char *path, bool quiet);
+int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type);
 int mount_bpffs_for_pin(const char *name);
 int do_pin_any(int argc, char **argv, int (*get_fd_by_id)(int *, char ***));
 int do_pin_fd(int fd, const char *name);
-- 
2.17.1

Re: [PATCH bpf-next v2] bpftool: use only nftw for file tree parsing

[Quentin Monnet]

2020-07-15 22:29 UTC-0700 ~ Tony Ambardar <tony.ambardar@gmail.com>
> The bpftool sources include code to walk file trees, but use multiple
> frameworks to do so: nftw and fts. While nftw conforms to POSIX/SUSv3 and
> is widely available, fts is not conformant and less common, especially on
> non-glibc systems. The inconsistent framework usage hampers maintenance
> and portability of bpftool, in particular for embedded systems.
> 
> Standardize code usage by rewriting one fts-based function to use nftw.
> Clean up related function warnings by using "const char *" arguments and
> fixing an unsafe call to dirname().
> 
> These changes help in building bpftool against musl for OpenWrt.

Could you please add a line to the log about the reason for the path
copy in open_obj_pinned()?

> 
> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> ---
> 
> V2:
> * use _GNU_SOURCE to pull in getpagesize(), getline(), nftw() definitions
> * use "const char *" in open_obj_pinned() and open_obj_pinned_any()
> * make dirname() safely act on a string copy
> 
> ---
>  tools/bpf/bpftool/common.c | 129 +++++++++++++++++++++----------------
>  tools/bpf/bpftool/main.h   |   4 +-
>  2 files changed, 76 insertions(+), 57 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
> index 29f4e7611ae8..7c2e52fc5784 100644
> --- a/tools/bpf/bpftool/common.c
> +++ b/tools/bpf/bpftool/common.c
> @@ -1,10 +1,11 @@
>  // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>  /* Copyright (C) 2017-2018 Netronome Systems, Inc. */
>  
> +#define _GNU_SOURCE
>  #include <ctype.h>
>  #include <errno.h>
>  #include <fcntl.h>
> -#include <fts.h>
> +#include <ftw.h>
>  #include <libgen.h>
>  #include <mntent.h>
>  #include <stdbool.h>
> @@ -160,24 +161,36 @@ int mount_tracefs(const char *target)
>  	return err;
>  }
>  
> -int open_obj_pinned(char *path, bool quiet)
> +int open_obj_pinned(const char *path, bool quiet)
>  {
> -	int fd;
> +	char *pname;
> +	int fd = -1;
> +
> +	pname = strdup(path);
> +	if (pname == NULL) {

Simply "if (!pname) {"

> +		if (!quiet)
> +			p_err("bpf obj get (%s): %s", path, strerror(errno));

Please update the error message, this one was for a failure on
bpf_obj_get().

> +		goto out_ret;
> +	}
> +

You're adding a second blank line here, please fix.

>  
> -	fd = bpf_obj_get(path);
> +	fd = bpf_obj_get(pname);
>  	if (fd < 0) {
>  		if (!quiet)
> -			p_err("bpf obj get (%s): %s", path,
> -			      errno == EACCES && !is_bpffs(dirname(path)) ?
> +			p_err("bpf obj get (%s): %s", pname,
> +			      errno == EACCES && !is_bpffs(dirname(pname)) ?
>  			    "directory not in bpf file system (bpffs)" :
>  			    strerror(errno));
> -		return -1;
> +		goto out_free;
>  	}
>  
> +out_free:
> +	free(pname);
> +out_ret:
>  	return fd;
>  }
>  
> -int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type)
> +int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type)
>  {
>  	enum bpf_obj_type type;
>  	int fd;
> @@ -367,68 +380,74 @@ void print_hex_data_json(uint8_t *data, size_t len)
>  	jsonw_end_array(json_wtr);
>  }
>  
> -int build_pinned_obj_table(struct pinned_obj_table *tab,
> -			   enum bpf_obj_type type)
> +static struct pinned_obj_table *build_fn_table; /* params for nftw cb*/
> +static enum bpf_obj_type build_fn_type;

I would move the comments above the lines, since it applies to both of them.

> +
> +static int do_build_table_cb(const char *fpath, const struct stat *sb,
> +			    int typeflag, struct FTW *ftwbuf)

Please align the second line on the open parenthesis.

>  {
>  	struct bpf_prog_info pinned_info = {};

A few suggestions on this code, even though I realise you simply moved
some parts. We can skip zero-initialising here (" = {}") because we
memset() it below before using it anyway.

>  	struct pinned_obj *obj_node = NULL;
>  	__u32 len = sizeof(pinned_info);
> -	struct mntent *mntent = NULL;
>  	enum bpf_obj_type objtype;
> +	int fd, err = 0;
> +
> +	if (typeflag != FTW_F)
> +		goto out_ret;
> +	fd = open_obj_pinned(fpath, true);
> +	if (fd < 0)
> +		goto out_ret;
> +
> +	objtype = get_fd_type(fd);
> +	if (objtype != build_fn_type)
> +		goto out_close;
> +
> +	memset(&pinned_info, 0, sizeof(pinned_info));
> +	if (bpf_obj_get_info_by_fd(fd, &pinned_info, &len)) {
> +		p_err("can't get obj info: %s", strerror(errno));

We are simply building a table here to show the paths where objects are
pinned when listing progs/maps/etc., and I don't believe we want to
print an error in that case. And with such a message I would expect the
function to return and bpftool to stop, but again I don't believe this
is necessary here and we can just go on listing objects, even if we fail
to show their pinned paths.

> +		goto out_close;
> +	}
> +
> +	obj_node = malloc(sizeof(*obj_node));
> +	if (!obj_node) {
> +		p_err("mem alloc failed");

Same here, let's not add an error message.

> +		err = -1;
> +		goto out_close;
> +	}
> +
> +	memset(obj_node, 0, sizeof(*obj_node));

Instead of malloc() + memset(), we could simply use calloc().

> +	obj_node->id = pinned_info.id;
> +	obj_node->path = strdup(fpath);
> +	hash_add(build_fn_table->table, &obj_node->hash, obj_node->id);
> +
> +out_close:
> +	close(fd);
> +out_ret:
> +	return err;
> +}
> +
> +int build_pinned_obj_table(struct pinned_obj_table *tab,
> +			   enum bpf_obj_type type)
> +{

The end looks good.

Apart from the minor points mentioned above, the patch is good, copying
the string in open_obj_pinned() looks like the right approach. It does
compile (with no warnings) and works as intended on my machine :).

Thanks,
Quentin

Re: [PATCH bpf-next v2] bpftool: use only nftw for file tree parsing

[Tony Ambardar]

On Thu, 16 Jul 2020 at 02:14, Quentin Monnet <quentin@isovalent.com> wrote:
>
> 2020-07-15 22:29 UTC-0700 ~ Tony Ambardar <tony.ambardar@gmail.com>
> > The bpftool sources include code to walk file trees, but use multiple
> > frameworks to do so: nftw and fts. While nftw conforms to POSIX/SUSv3 and
> > is widely available, fts is not conformant and less common, especially on
> > non-glibc systems. The inconsistent framework usage hampers maintenance
> > and portability of bpftool, in particular for embedded systems.
> >
> > Standardize code usage by rewriting one fts-based function to use nftw.
> > Clean up related function warnings by using "const char *" arguments and
> > fixing an unsafe call to dirname().
> >
> > These changes help in building bpftool against musl for OpenWrt.
>
> Could you please add a line to the log about the reason for the path
> copy in open_obj_pinned()?

Good point, will do.

> >
> > Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> > ---
> >
> > V2:
> > * use _GNU_SOURCE to pull in getpagesize(), getline(), nftw() definitions
> > * use "const char *" in open_obj_pinned() and open_obj_pinned_any()
> > * make dirname() safely act on a string copy
> >
> > ---
> >  tools/bpf/bpftool/common.c | 129 +++++++++++++++++++++----------------
> >  tools/bpf/bpftool/main.h   |   4 +-
> >  2 files changed, 76 insertions(+), 57 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
> > index 29f4e7611ae8..7c2e52fc5784 100644
> > --- a/tools/bpf/bpftool/common.c
> > +++ b/tools/bpf/bpftool/common.c
> > @@ -1,10 +1,11 @@
> >  // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> >  /* Copyright (C) 2017-2018 Netronome Systems, Inc. */
> >
> > +#define _GNU_SOURCE
> >  #include <ctype.h>
> >  #include <errno.h>
> >  #include <fcntl.h>
> > -#include <fts.h>
> > +#include <ftw.h>
> >  #include <libgen.h>
> >  #include <mntent.h>
> >  #include <stdbool.h>
> > @@ -160,24 +161,36 @@ int mount_tracefs(const char *target)
> >       return err;
> >  }
> >
> > -int open_obj_pinned(char *path, bool quiet)
> > +int open_obj_pinned(const char *path, bool quiet)
> >  {
> > -     int fd;
> > +     char *pname;
> > +     int fd = -1;
> > +
> > +     pname = strdup(path);
> > +     if (pname == NULL) {
>
> Simply "if (!pname) {"
>
> > +             if (!quiet)
> > +                     p_err("bpf obj get (%s): %s", path, strerror(errno));
>
> Please update the error message, this one was for a failure on
> bpf_obj_get().
>
> > +             goto out_ret;
> > +     }
> > +
>
> You're adding a second blank line here, please fix.
>
> >
> > -     fd = bpf_obj_get(path);
> > +     fd = bpf_obj_get(pname);
> >       if (fd < 0) {
> >               if (!quiet)
> > -                     p_err("bpf obj get (%s): %s", path,
> > -                           errno == EACCES && !is_bpffs(dirname(path)) ?
> > +                     p_err("bpf obj get (%s): %s", pname,
> > +                           errno == EACCES && !is_bpffs(dirname(pname)) ?
> >                           "directory not in bpf file system (bpffs)" :
> >                           strerror(errno));
> > -             return -1;
> > +             goto out_free;
> >       }
> >
> > +out_free:
> > +     free(pname);
> > +out_ret:
> >       return fd;
> >  }
> >
> > -int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type)
> > +int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type)
> >  {
> >       enum bpf_obj_type type;
> >       int fd;
> > @@ -367,68 +380,74 @@ void print_hex_data_json(uint8_t *data, size_t len)
> >       jsonw_end_array(json_wtr);
> >  }
> >
> > -int build_pinned_obj_table(struct pinned_obj_table *tab,
> > -                        enum bpf_obj_type type)
> > +static struct pinned_obj_table *build_fn_table; /* params for nftw cb*/
> > +static enum bpf_obj_type build_fn_type;
>
> I would move the comments above the lines, since it applies to both of them.
>
> > +
> > +static int do_build_table_cb(const char *fpath, const struct stat *sb,
> > +                         int typeflag, struct FTW *ftwbuf)
>
> Please align the second line on the open parenthesis.
>
> >  {
> >       struct bpf_prog_info pinned_info = {};
>
> A few suggestions on this code, even though I realise you simply moved
> some parts. We can skip zero-initialising here (" = {}") because we
> memset() it below before using it anyway.
>
> >       struct pinned_obj *obj_node = NULL;
> >       __u32 len = sizeof(pinned_info);
> > -     struct mntent *mntent = NULL;
> >       enum bpf_obj_type objtype;
> > +     int fd, err = 0;
> > +
> > +     if (typeflag != FTW_F)
> > +             goto out_ret;
> > +     fd = open_obj_pinned(fpath, true);
> > +     if (fd < 0)
> > +             goto out_ret;
> > +
> > +     objtype = get_fd_type(fd);
> > +     if (objtype != build_fn_type)
> > +             goto out_close;
> > +
> > +     memset(&pinned_info, 0, sizeof(pinned_info));
> > +     if (bpf_obj_get_info_by_fd(fd, &pinned_info, &len)) {
> > +             p_err("can't get obj info: %s", strerror(errno));
>
> We are simply building a table here to show the paths where objects are
> pinned when listing progs/maps/etc., and I don't believe we want to
> print an error in that case. And with such a message I would expect the
> function to return and bpftool to stop, but again I don't believe this
> is necessary here and we can just go on listing objects, even if we fail
> to show their pinned paths.
>
> > +             goto out_close;
> > +     }
> > +
> > +     obj_node = malloc(sizeof(*obj_node));
> > +     if (!obj_node) {
> > +             p_err("mem alloc failed");
>
> Same here, let's not add an error message.

You're right. I just realized those aren't pre-existing messages; I
added them but then forgot.

> > +             err = -1;
> > +             goto out_close;
> > +     }
> > +
> > +     memset(obj_node, 0, sizeof(*obj_node));
>
> Instead of malloc() + memset(), we could simply use calloc().
>
> > +     obj_node->id = pinned_info.id;
> > +     obj_node->path = strdup(fpath);

I should check for failed allocation here too.

> > +     hash_add(build_fn_table->table, &obj_node->hash, obj_node->id);
> > +
> > +out_close:
> > +     close(fd);
> > +out_ret:
> > +     return err;
> > +}
> > +
> > +int build_pinned_obj_table(struct pinned_obj_table *tab,
> > +                        enum bpf_obj_type type)
> > +{
>
> The end looks good.
>
> Apart from the minor points mentioned above, the patch is good, copying
> the string in open_obj_pinned() looks like the right approach. It does
> compile (with no warnings) and works as intended on my machine :).

Glad to hear it! I'll update the patch based on your comments above
and resend shortly. Thanks again for the testing and feedback.

Regards,
Tony

> Thanks,
> Quentin