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Message-ID: <20241014121047.103179-1-brgl@bgdev.pl>
Date: Mon, 14 Oct 2024 14:10:47 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Linus Walleij <linus.walleij@...aro.org>,
Kent Gibson <warthog618@...il.com>
Cc: linux-gpio@...r.kernel.org,
linux-kernel@...r.kernel.org,
Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH] gpio: create empty /sys/class/gpio with SYSFS disabled
From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
User-space may want to use some kind of a compatibility layer for the
deprecated GPIO sysfs ABI. This would typically involve mounting
a fuse-based filesystem using the GPIO character device to emulate the
sysfs behavior and layout.
With GPIO_SYSFS disabled, the /sys/class/gpio directory doesn't exist
and user-space cannot create it. In order to facilitate moving away from
the sysfs, add a new Kconfig option that indicates to GPIOLIB that is
should create an empty directory where the GPIO class interface would
exist and enable it by default.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
As I've mentioned under a different patch, I'm working on a user-space
compatibility layer for the sysfs GPIO interface. FUSE allows us to
emulate almost all its functionalities using libgpiod except for
mounting it under /sys/class/gpio if GPIO_SYSFS is disabled. User-space
cannot create directories in sysfs so if we want to allow users to mount
the FUSE emulator under the old location, we need to create an empty
/sys/class/gpio directory from the kernel and this is what is patch is
for.
drivers/gpio/Kconfig | 18 ++++++++++++++++++
drivers/gpio/gpiolib.c | 12 ++++++++++++
2 files changed, 30 insertions(+)
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index bfa6b5a2c537..f2e7163cb46c 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -69,6 +69,24 @@ config GPIO_SYSFS
use the character device /dev/gpiochipN with the appropriate
ioctl() operations instead.
+config GPIO_SYSFS_CLASS_DIR_STUB
+ bool "Create empty /sys/class/gpio directory" if EXPERT
+ depends on !GPIO_SYSFS
+ default y
+ help
+ Say Y here to create an empty /sys/class/gpio directory.
+
+ User-space may want to use some kind of a compatibility layer for the
+ deprecated GPIO sysfs ABI. This would typically involve mounting
+ a fuse-based filesystem using the GPIO character device to emulate
+ the sysfs behavior and layout.
+
+ This option makes GPIOLIB create an empty directory at /sys/class/gpio
+ where user-space can mount the sysfs replacement and avoid having to
+ change existing programs to adjust to different filesystem paths.
+
+ If unsure, say Y.
+
config GPIO_CDEV
bool
prompt "Character device (/dev/gpiochipN) support" if EXPERT
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 97346b746ef5..31efb580beb8 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4873,6 +4873,12 @@ static struct device_driver gpio_stub_drv = {
.probe = gpio_stub_drv_probe,
};
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_CLASS_DIR_STUB)
+static const struct class gpio_class_stub = {
+ .name = "gpio",
+};
+#endif /* CONFIG_GPIO_SYSFS_CLASS_DIR_STUB */
+
static int __init gpiolib_dev_init(void)
{
int ret;
@@ -4899,6 +4905,12 @@ static int __init gpiolib_dev_init(void)
return ret;
}
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_CLASS_DIR_STUB)
+ ret = class_register(&gpio_class_stub);
+ if (ret)
+ pr_err("gpiolib: failed to create the empty gpio class directory\n");
+#endif /* CONFIG_GPIO_SYSFS_CLASS_DIR_STUB */
+
gpiolib_initialized = true;
gpiochip_setup_devs();
--
2.43.0
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