[PATCH bpf-next v3] bpftool: Mount bpffs on provided dir instead of parent dir

[PATCH bpf-next v3] bpftool: Mount bpffs on provided dir instead of parent dir

[Sahil Siddiq]

When pinning programs/objects under PATH (eg: during "bpftool prog
loadall") the bpffs is mounted on the parent dir of PATH in the
following situations:
- the given dir exists but it is not bpffs.
- the given dir doesn't exist and the parent dir is not bpffs.

Mounting on the parent dir can also have the unintentional side-
effect of hiding other files located under the parent dir.

If the given dir exists but is not bpffs, then the bpffs should
be mounted on the given dir and not its parent dir.

Similarly, if the given dir doesn't exist and its parent dir is not
bpffs, then the given dir should be created and the bpffs should be
mounted on this new dir.

Link: https://lore.kernel.org/bpf/2da44d24-74ae-a564-1764-afccf395eeec@isovalent.com/T/#t
Closes: https://github.com/libbpf/bpftool/issues/100
Fixes: 2a36c26fe3b8 ("bpftool: Support bpffs mountpoint as pin path for prog loadall")

Changes since v1:
 - Split "mount_bpffs_for_pin" into two functions.
   This is done to improve maintainability and readability.

Changes since v2:
- mount_bpffs_for_pin: rename to "create_and_mount_bpffs_dir".
- mount_bpffs_given_file: rename to "mount_bpffs_given_file".
- create_and_mount_bpffs_dir:
  - introduce "dir_exists" boolean.
  - remove new dir if "mnt_fs" fails.
- improve error handling and error messages.

Signed-off-by: Sahil Siddiq <icegambit91@gmail.com>
---
 tools/bpf/bpftool/common.c     | 93 ++++++++++++++++++++++++++++++----
 tools/bpf/bpftool/iter.c       |  2 +-
 tools/bpf/bpftool/main.h       |  3 +-
 tools/bpf/bpftool/prog.c       |  5 +-
 tools/bpf/bpftool/struct_ops.c |  2 +-
 5 files changed, 90 insertions(+), 15 deletions(-)

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index cc6e6aae2447..dce73105b0a5 100644
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -244,24 +244,95 @@ int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type)
 	return fd;
 }
 
-int mount_bpffs_for_pin(const char *name, bool is_dir)
+int create_and_mount_bpffs_dir(const char *dir_name)
 {
 	char err_str[ERR_MAX_LEN];
-	char *file;
-	char *dir;
 	int err = 0;
+	bool dir_exists;
 
-	if (is_dir && is_bpffs(name))
+	if (is_bpffs(dir_name))
 		return err;
 
-	file = malloc(strlen(name) + 1);
-	if (!file) {
+	dir_exists = (access(dir_name, F_OK) == 0);
+
+	if (!dir_exists) {
+		char *temp_name;
+		char *parent_name;
+
+		temp_name = malloc(strlen(dir_name) + 1);
+		if (!temp_name) {
+			p_err("mem alloc failed");
+			return -1;
+		}
+
+		strcpy(temp_name, dir_name);
+		parent_name = dirname(temp_name);
+
+		if (is_bpffs(parent_name)) {
+			/* nothing to do if already mounted */
+			free(temp_name);
+			return err;
+		}
+
+		if (access(parent_name, F_OK) == -1) {
+			p_err("bpf object can't be pinned since dir (%s) does not exist",
+			      parent_name);
+			free(temp_name);
+			return -1;
+		}
+
+		free(temp_name);
+	}
+
+	if (block_mount) {
+		p_err("no BPF file system found, not mounting it due to --nomount option");
+		return -1;
+	}
+
+	if (!dir_exists) {
+		err = mkdir(dir_name, 0700);
+		if (err) {
+			p_err("failed to create dir (%s): %s", dir_name, strerror(errno));
+			return err;
+		}
+	}
+
+	err = mnt_fs(dir_name, "bpf", err_str, ERR_MAX_LEN);
+	if (err) {
+		err_str[ERR_MAX_LEN - 1] = '\0';
+		p_err("can't mount BPF file system on given dir (%s): %s",
+		      dir_name, err_str);
+
+		if (!dir_exists) {
+			if (rmdir(dir_name) == -1)
+				p_err("failed to remove newly created dir (%s): %s",
+				      dir_name, strerror(errno));
+		}
+	}
+
+	return err;
+}
+
+int mount_bpffs_given_file(const char *file_name)
+{
+	char err_str[ERR_MAX_LEN];
+	char *temp_name;
+	char *dir;
+	int err = 0;
+
+	if (access(file_name, F_OK) != -1) {
+		p_err("bpf object can't be pinned since file (%s) already exists", file_name);
+		return -1;
+	}
+
+	temp_name = malloc(strlen(file_name) + 1);
+	if (!temp_name) {
 		p_err("mem alloc failed");
 		return -1;
 	}
 
-	strcpy(file, name);
-	dir = dirname(file);
+	strcpy(temp_name, file_name);
+	dir = dirname(temp_name);
 
 	if (is_bpffs(dir))
 		/* nothing to do if already mounted */
@@ -277,11 +348,11 @@ int mount_bpffs_for_pin(const char *name, bool is_dir)
 	if (err) {
 		err_str[ERR_MAX_LEN - 1] = '\0';
 		p_err("can't mount BPF file system to pin the object (%s): %s",
-		      name, err_str);
+		      file_name, err_str);
 	}
 
 out_free:
-	free(file);
+	free(temp_name);
 	return err;
 }
 
@@ -289,7 +360,7 @@ int do_pin_fd(int fd, const char *name)
 {
 	int err;
 
-	err = mount_bpffs_for_pin(name, false);
+	err = mount_bpffs_for_file(name);
 	if (err)
 		return err;
 
diff --git a/tools/bpf/bpftool/iter.c b/tools/bpf/bpftool/iter.c
index 6b0e5202ca7a..5c39c2ed36a2 100644
--- a/tools/bpf/bpftool/iter.c
+++ b/tools/bpf/bpftool/iter.c
@@ -76,7 +76,7 @@ static int do_pin(int argc, char **argv)
 		goto close_obj;
 	}
 
-	err = mount_bpffs_for_pin(path, false);
+	err = mount_bpffs_for_file(path);
 	if (err)
 		goto close_link;
 
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index b8bb08d10dec..9eb764fe4cc8 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -142,7 +142,8 @@ const char *get_fd_type_name(enum bpf_obj_type type);
 char *get_fdinfo(int fd, const char *key);
 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, bool is_dir);
+int mount_bpffs_for_file(const char *file_name);
+int create_and_mount_bpffs_dir(const char *dir_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);
 
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 9cb42a3366c0..4c4cf16a40ba 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1778,7 +1778,10 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 		goto err_close_obj;
 	}
 
-	err = mount_bpffs_for_pin(pinfile, !first_prog_only);
+	if (first_prog_only)
+		err = mount_bpffs_for_file(pinfile);
+	else
+		err = create_and_mount_bpffs_dir(pinfile);
 	if (err)
 		goto err_close_obj;
 
diff --git a/tools/bpf/bpftool/struct_ops.c b/tools/bpf/bpftool/struct_ops.c
index d573f2640d8e..aa43dead249c 100644
--- a/tools/bpf/bpftool/struct_ops.c
+++ b/tools/bpf/bpftool/struct_ops.c
@@ -515,7 +515,7 @@ static int do_register(int argc, char **argv)
 	if (argc == 1)
 		linkdir = GET_ARG();
 
-	if (linkdir && mount_bpffs_for_pin(linkdir, true)) {
+	if (linkdir && create_and_mount_bpffs_dir(linkdir)) {
 		p_err("can't mount bpffs for pinning");
 		return -1;
 	}
-- 
2.44.0

Re: [PATCH bpf-next v3] bpftool: Mount bpffs on provided dir instead of parent dir

[Quentin Monnet]

Hi Sahil, sorry for the delay, and thanks for the v3! I've got some 
minor comments on the error messages, but the rest of the code looks 
mostly good - although you forgot to rename a function and it currently 
fails to compile. Please see inline below.

On 21/03/2024 19:19, Sahil Siddiq wrote:
> When pinning programs/objects under PATH (eg: during "bpftool prog
> loadall") the bpffs is mounted on the parent dir of PATH in the
> following situations:
> - the given dir exists but it is not bpffs.
> - the given dir doesn't exist and the parent dir is not bpffs.
> 
> Mounting on the parent dir can also have the unintentional side-
> effect of hiding other files located under the parent dir.
> 
> If the given dir exists but is not bpffs, then the bpffs should
> be mounted on the given dir and not its parent dir.
> 
> Similarly, if the given dir doesn't exist and its parent dir is not
> bpffs, then the given dir should be created and the bpffs should be
> mounted on this new dir.
> 
> Link: https://lore.kernel.org/bpf/2da44d24-74ae-a564-1764-afccf395eeec@isovalent.com/T/#t
> Closes: https://github.com/libbpf/bpftool/issues/100
> Fixes: 2a36c26fe3b8 ("bpftool: Support bpffs mountpoint as pin path for prog loadall")
> 
> Changes since v1:
>   - Split "mount_bpffs_for_pin" into two functions.
>     This is done to improve maintainability and readability.
> 
> Changes since v2:
> - mount_bpffs_for_pin: rename to "create_and_mount_bpffs_dir".
> - mount_bpffs_given_file: rename to "mount_bpffs_given_file".

That's the same!

> - create_and_mount_bpffs_dir:
>    - introduce "dir_exists" boolean.
>    - remove new dir if "mnt_fs" fails.
> - improve error handling and error messages.
> 
> Signed-off-by: Sahil Siddiq <icegambit91@gmail.com>
> ---
>   tools/bpf/bpftool/common.c     | 93 ++++++++++++++++++++++++++++++----
>   tools/bpf/bpftool/iter.c       |  2 +-
>   tools/bpf/bpftool/main.h       |  3 +-
>   tools/bpf/bpftool/prog.c       |  5 +-
>   tools/bpf/bpftool/struct_ops.c |  2 +-
>   5 files changed, 90 insertions(+), 15 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
> index cc6e6aae2447..dce73105b0a5 100644
> --- a/tools/bpf/bpftool/common.c
> +++ b/tools/bpf/bpftool/common.c
> @@ -244,24 +244,95 @@ int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type)
>   	return fd;
>   }
>   
> -int mount_bpffs_for_pin(const char *name, bool is_dir)
> +int create_and_mount_bpffs_dir(const char *dir_name)
>   {
>   	char err_str[ERR_MAX_LEN];
> -	char *file;
> -	char *dir;
>   	int err = 0;
> +	bool dir_exists;

Nit: "reverse Christmas tree order": In the absence of other criteria, 
we tend to sort the variable definitions by line length. Please swap 
dir_exists and err.

>   
> -	if (is_dir && is_bpffs(name))
> +	if (is_bpffs(dir_name))
>   		return err;
>   
> -	file = malloc(strlen(name) + 1);
> -	if (!file) {
> +	dir_exists = (access(dir_name, F_OK) == 0);
> +
> +	if (!dir_exists) {
> +		char *temp_name;
> +		char *parent_name;
> +
> +		temp_name = malloc(strlen(dir_name) + 1);
> +		if (!temp_name) {
> +			p_err("mem alloc failed");
> +			return -1;
> +		}
> +
> +		strcpy(temp_name, dir_name);
> +		parent_name = dirname(temp_name);
> +
> +		if (is_bpffs(parent_name)) {
> +			/* nothing to do if already mounted */
> +			free(temp_name);
> +			return err;
> +		}
> +
> +		if (access(parent_name, F_OK) == -1) {
> +			p_err("bpf object can't be pinned since dir (%s) does not exist",

Maybe "can't create directory '%s' to pin BPF object: parent dir %s does 
not exist"?

> +			      parent_name);
> +			free(temp_name);
> +			return -1;
> +		}
> +
> +		free(temp_name);
> +	}
> +
> +	if (block_mount) {
> +		p_err("no BPF file system found, not mounting it due to --nomount option");
> +		return -1;
> +	}
> +
> +	if (!dir_exists) {
> +		err = mkdir(dir_name, 0700);
> +		if (err) {
> +			p_err("failed to create dir (%s): %s", dir_name, strerror(errno));

Or "failed to create directory '%s': %s".

> +			return err;
> +		}
> +	}
> +
> +	err = mnt_fs(dir_name, "bpf", err_str, ERR_MAX_LEN);
> +	if (err) {
> +		err_str[ERR_MAX_LEN - 1] = '\0';
> +		p_err("can't mount BPF file system on given dir (%s): %s",
> +		      dir_name, err_str);
> +
> +		if (!dir_exists) {
> +			if (rmdir(dir_name) == -1)
> +				p_err("failed to remove newly created dir (%s): %s",
> +				      dir_name, strerror(errno));

We're already on an error path, I'd maybe drop the check on the return 
value from rmdir(). It doesn't matter much if it fails, I think.

> +		}
> +	}
> +
> +	return err;
> +}
> +
> +int mount_bpffs_given_file(const char *file_name)

This function must be renamed, as you did at the call sites.

> +{
> +	char err_str[ERR_MAX_LEN];
> +	char *temp_name;
> +	char *dir;
> +	int err = 0;
> +
> +	if (access(file_name, F_OK) != -1) {
> +		p_err("bpf object can't be pinned since file (%s) already exists", file_name);

Not sure why the parenthesis, let's use quotes? Can we also replace 
"since" with "because", or "given that", or simply a colon, please? And 
I'd drop the passive voice, here's what I would use:

     "can't pin BPF object: path '%s' already exists"

> +		return -1;
> +	}
> +
> +	temp_name = malloc(strlen(file_name) + 1);
> +	if (!temp_name) {
>   		p_err("mem alloc failed");
>   		return -1;
>   	}
>   
> -	strcpy(file, name);
> -	dir = dirname(file);
> +	strcpy(temp_name, file_name);
> +	dir = dirname(temp_name);
>   
>   	if (is_bpffs(dir))
>   		/* nothing to do if already mounted */
> @@ -277,11 +348,11 @@ int mount_bpffs_for_pin(const char *name, bool is_dir)
>   	if (err) {
>   		err_str[ERR_MAX_LEN - 1] = '\0';
>   		p_err("can't mount BPF file system to pin the object (%s): %s",

"object '%s'" instead of "the object (%s)" please.

> -		      name, err_str);
> +		      file_name, err_str);
>   	}
>   
>   out_free:
> -	free(file);
> +	free(temp_name);
>   	return err;
>   }
>   
> @@ -289,7 +360,7 @@ int do_pin_fd(int fd, const char *name)
>   {
>   	int err;
>   
> -	err = mount_bpffs_for_pin(name, false);
> +	err = mount_bpffs_for_file(name);

Compiler says "undefined reference to `mount_bpffs_for_file`", please 
build and test your patch. See also how most CI jobs fail:
https://github.com/kernel-patches/bpf/pull/6614

Quentin

Re: [PATCH bpf-next v3] bpftool: Mount bpffs on provided dir instead of parent dir

[Sahil]

Hi,

Thank you for the review. I have refactored the error messages. I have
removed a few more parantheses.

On Wednesday, March 27, 2024 6:44:52 AM IST Quentin Monnet wrote:
> [...]
> We're already on an error path, I'd maybe drop the check on the return
> value from rmdir(). It doesn't matter much if it fails, I think.

I was thinking that if we fail to mount but manage to create the dir
successfully, then we should also clean up that new dir and send a
notification if we fail to remove that dir so the user can manually
remove it.

I guess it's ok to remove that error message though since dealing with
the "fail to mount" error will anyway require manual intervention.

> [...]
> This function must be renamed, as you did at the call sites.

Sorry, I must have forgotten to copy this when copying the changes
from the bpftool repo to my local bpf-next tree.

Thanks,
Sahil