The Linux Debug File System is a virtual memory File system that was developed so that debug kernel information can be accessed in user space whenever desired. It is a RAM based File system.
The Debug File system will be enabled in the Linux kernel build if “CONFIG_DEBUG_FS” is enabled in the kernel config. The debug file system is mounted at mount point “/sys/kernel/debug”.
The Debug File System can be mounted dynamically with a command like –
- mount -t debugfs none /sys/kernel/debug
a couple properties of the Debug File System is provided below
- debugFS directory is only accessible to root user
- Unlike procfs and sysfs which has one value per file rule, debugfs does not have such a limitation
To create a debug File System access to a kernel module, APIs are present. A few APIs are provided below
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Debug FS API |
Description |
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struct dentry *debugfs_create_dir(const char *name, struct dentry *parent) |
This will create a directory called “name” underneath the indicated parent directory. |
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struct dentry *debugfs_create_file(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops); |
Creates a debug file in the “parent” directory |
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struct dentry *debugfs_create_file_size(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops, loff_t file_size); |
Create a debug File with an initial File size |
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void debugfs_remove(struct dentry *dentry); |
Remove an entry from debug FS |
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void debugfs_remove_recursive(struct dentry *dentry); |
Remove the entire hierarchy of files |
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struct dentry *debugfs_create_u8(const char *name, mode_t mode, struct dentry *parent, u8 *value);
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Create an entry to export a u8 value |
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struct dentry *debugfs_create_u16(const char *name, mode_t mode, struct dentry *parent, u16 *value);
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Create an entry to export a u16 value |
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struct dentry *debugfs_create_u32(const char *name, mode_t mode, struct dentry *parent, u32 *value);
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Create an entry to export a u32 value
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struct dentry *debugfs_create_bool(const char *name, mode_t mode, struct dentry *parent, u32 *value);
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Create an entry to export a bool value |
In addition, a number of support APIs are provided to create specific file types. The below links provide the interested reader with a list of the different APIs that are supported and further information on debugfs.
- https://www.kernel.org/doc/html/latest/filesystems/debugfs.html
- https://www.kernel.org/doc/html/latest/filesystems/debugfs.html
Linux Kernel – Adding DebugFS support to a Linux kernel module
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