Handling Errors and Return Codes
In kernel development, robust error handling is crucial for both system stability and debugging. The kernel uses a set of standard error codes, typically defined in errno.h, to indicate various failure conditions. These codes are negative integers, such as -ENOMEM for Out of memory, -EFAULT for Bad address, and -EINVAL for Invalid argument. Returning these codes consistently allows kernel and user space to understand what went wrong and respond appropriately.
error_code_demo.c
1234567891011121314151617181920212223242526272829303132333435363738#include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> #include <linux/errno.h> static int allocate_resource(int should_fail) { if (should_fail) return -ENOMEM; // Out of memory // Simulate success return 0; } static int __init error_code_demo_init(void) { int ret; ret = allocate_resource(1); if (ret) { printk(KERN_ERR "allocate_resource failed: %d\n", ret); return ret; } printk(KERN_INFO "allocate_resource succeeded\n"); return 0; } static void __exit error_code_demo_exit(void) { printk(KERN_INFO "Exiting error code demo module\n"); } module_init(error_code_demo_init); module_exit(error_code_demo_exit); MODULE_LICENSE("GPL"); MODULE_AUTHOR("Device Driver Course"); MODULE_DESCRIPTION("Demo of returning standard kernel error codes");
When writing driver functions, you should propagate error codes up the call chain so that the kernel or calling process can handle them appropriately. In the code above, the allocate_resource function returns -ENOMEM if it simulates a failure. The module's init function receives this code and returns it to the kernel, ensuring that the error is not silently ignored. This pattern is common in kernel code: check for errors after each operation, and return the error code immediately if one occurs. This approach helps maintain clarity and reliability in driver logic.
demo_read.c
1234567891011121314151617#include <linux/fs.h> #include <linux/uaccess.h> #include <linux/errno.h> ssize_t demo_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos) { char kernel_buffer[100] = "Sample data from kernel"; size_t datalen = strlen(kernel_buffer); if (count < datalen) return -EINVAL; // Invalid argument: buffer too small if (copy_to_user(buf, kernel_buffer, datalen)) return -EFAULT; // Failed to copy data to user return datalen; // Success: return number of bytes read }
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In kernel development, robust error handling is crucial for both system stability and debugging. The kernel uses a set of standard error codes, typically defined in errno.h, to indicate various failure conditions. These codes are negative integers, such as -ENOMEM for Out of memory, -EFAULT for Bad address, and -EINVAL for Invalid argument. Returning these codes consistently allows kernel and user space to understand what went wrong and respond appropriately.
error_code_demo.c
1234567891011121314151617181920212223242526272829303132333435363738#include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> #include <linux/errno.h> static int allocate_resource(int should_fail) { if (should_fail) return -ENOMEM; // Out of memory // Simulate success return 0; } static int __init error_code_demo_init(void) { int ret; ret = allocate_resource(1); if (ret) { printk(KERN_ERR "allocate_resource failed: %d\n", ret); return ret; } printk(KERN_INFO "allocate_resource succeeded\n"); return 0; } static void __exit error_code_demo_exit(void) { printk(KERN_INFO "Exiting error code demo module\n"); } module_init(error_code_demo_init); module_exit(error_code_demo_exit); MODULE_LICENSE("GPL"); MODULE_AUTHOR("Device Driver Course"); MODULE_DESCRIPTION("Demo of returning standard kernel error codes");
When writing driver functions, you should propagate error codes up the call chain so that the kernel or calling process can handle them appropriately. In the code above, the allocate_resource function returns -ENOMEM if it simulates a failure. The module's init function receives this code and returns it to the kernel, ensuring that the error is not silently ignored. This pattern is common in kernel code: check for errors after each operation, and return the error code immediately if one occurs. This approach helps maintain clarity and reliability in driver logic.
demo_read.c
1234567891011121314151617#include <linux/fs.h> #include <linux/uaccess.h> #include <linux/errno.h> ssize_t demo_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos) { char kernel_buffer[100] = "Sample data from kernel"; size_t datalen = strlen(kernel_buffer); if (count < datalen) return -EINVAL; // Invalid argument: buffer too small if (copy_to_user(buf, kernel_buffer, datalen)) return -EFAULT; // Failed to copy data to user return datalen; // Success: return number of bytes read }
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