[PATCH i-g-t 1/2] lib/igt_configfs: Add library for configfs

[Louis Chauvet]

Hi Riana,

Le 10/04/2025 à 08:07, Riana Tauro a écrit :
> Add library functions to open configfs and create
> and remove configfs directories.

Can you take a look at [1], something similar was proposed few weeks 
ago? The main difference is that [1] checks that /sys/kernel/config is 
actually a mount point.

+Cc: José Exposito

[1]:https://lore.kernel.org/all/20250218165011.9123-4-jose.exposito89@gmail.com/

> Signed-off-by: Riana Tauro <riana.tauro at intel.com>
> ---
>   lib/igt_configfs.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++
>   lib/igt_configfs.h | 13 +++++++
>   lib/meson.build    |  1 +
>   3 files changed, 102 insertions(+)
>   create mode 100644 lib/igt_configfs.c
>   create mode 100644 lib/igt_configfs.h
> 
> diff --git a/lib/igt_configfs.c b/lib/igt_configfs.c
> new file mode 100644
> index 000000000..57d59f1c4
> --- /dev/null
> +++ b/lib/igt_configfs.c
> @@ -0,0 +1,88 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright © 2025 Intel Corporation
> + */
> +#include <sys/mount.h>
> +#include <sys/stat.h>
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <limits.h>
> +
> +#include "igt_configfs.h"
> +#include "igt_core.h"
> +
> +static const char *igt_configfs_mount(void)
> +{
> +	struct stat st;
> +
> +	if (stat("/sys/kernel/debug", &st) == 0)
> +		return "/sys/kernel/config";
> +
> +	if (mount("none", "/sys/kernel/config", "configfs", 0, 0))
> +		return NULL;
> +
> +	return "/sys/kernel/config";
> +}
> +
> +/**
> + * igt_configfs_open: open configfs path
> + * @name: name of the configfs directory
> + *
> + * Opens the configfs directory corresponding to the name
> + *
> + * Returns:
> + * The directory fd, or -1 on failure.
> + */
> +int igt_configfs_open(const char *name)
> +{
> +	char path[PATH_MAX];
> +	const char *configfs_path;
> +
> +	configfs_path = igt_configfs_mount();
> +	igt_assert(configfs_path);
> +
> +	snprintf(path, sizeof(path), "%s/%s", configfs_path, name);
> +
> +	return open(path, O_RDONLY);
> +}

The usage of file descriptors for folders is nice here!

@José, I think this may reduce the complexity of the vkms tests. At 
least it will avoid having snprintf(%s/%s, vkms_root, vkms_item). What 
do you think?

> +
> +/**
> + * igt_configfs_create_directory: creates configfs group
> + * @fd: fd of configfs parent directory
> + * @name: name of the directory to create
> + *
> + * creates a directory under configfs parent directory
> + *
> + * Returns: 0 on success, -errno otherwise

This seems wrong, as the function returns a file descriptor, did I miss 
something?

> + */
> +int igt_configfs_create_directory(int fd, const char *name)
> +{
> +	int ret;
> +	int dirfd;
> +
> +	ret = mkdirat(fd, name, 0755);
> +	if (ret)
> +		return -errno;
> +
> +	dirfd = openat(fd, name, O_DIRECTORY);
> +	if (dirfd < 0)
> +		return -errno;
> +
> +	return dirfd;
> +}
> +
> +/**
> + * igt_configfs_remove_directory: removes configfs group
> + * @fd: fd of configfs parent directory
> + * @name: name of directory to create
> + *
> + * removes directory under configfs parent directory
> + */
> +void igt_configfs_remove_directory(int fd, const char *name)
> +{
> +	int ret = unlinkat(fd, name, AT_REMOVEDIR);
> +
> +	if (ret)
> +		igt_warn("Unable to remove %s directory: %s\n", name, strerror(errno));
> +}

I completely understand the point of those helpers, but I don't think 
they are configfs-specific. The file descriptor is passed by argument, 
so you could use it for any interface (configfs, debugfs, sysfs...).

I don't see any igt_fs.c, do you think it beneficial to create such file?

@José, do you think it make sense to also reuse igt_sysfs helpers for 
the VKMS tests? (igt_sysfs_get/set_s32/u32/boolean only use a directory 
fd + path, if you decide to use fd for vkms, it will avoid code duplication)

Thanks a lot Riana for this implementation and new ideas.

Louis Chauvet

> diff --git a/lib/igt_configfs.h b/lib/igt_configfs.h
> new file mode 100644
> index 000000000..d839db49a
> --- /dev/null
> +++ b/lib/igt_configfs.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: MIT */
> +/*
> + * Copyright © 2025 Intel Corporation
> + */
> +
> +#ifndef IGT_CONFIGFS_H
> +#define IGT_CONFIGFS_H
> +
> +int igt_configfs_open(const char *name);
> +int igt_configfs_create_directory(int fd, const char *name);
> +void igt_configfs_remove_directory(int fd, const char *name);
> +
> +#endif /* IGT_CONFIGFS_H */
> diff --git a/lib/meson.build b/lib/meson.build
> index d7bb72c57..f087947e7 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -19,6 +19,7 @@ lib_sources = [
>   	'igt_collection.c',
>   	'igt_color_encoding.c',
>   	'igt_facts.c',
> +	'igt_configfs.c',
>   	'igt_crc.c',
>   	'igt_debugfs.c',
>   	'igt_device.c',

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com