// kernel style: tabs, 80 columns, spaces around operators

#include <linux/kernel.h>
#include <linux/slab.h>

struct device_data {
        struct list_head list;
        unsigned long flags;
        void __iomem *base;
        int irq;
};

static int device_init(struct device_data *dev)
{
        int ret;

        dev->base = ioremap(DEVICE_BASE, DEVICE_SIZE);
        if (!dev->base) {
                pr_err("Failed to map device memory\n");
                return -ENOMEM;
        }

        ret = request_irq(dev->irq, device_handler, 0, "mydev", dev);
        if (ret) {
                iounmap(dev->base);
                return ret;
        }

        return 0;
}

// BAD: Linked list for frequently traversed data
struct node {
    struct node *next;
    int value;
};

// Traversal: terrible cache behavior
// Each node is a cache miss

// GOOD: Array-based for cache locality
struct array {
    int *values;
    size_t count;
    size_t capacity;
};

// Traversal: sequential memory access
// Prefetcher works, cache is happy


// When you need linked lists, use the kernel's
#include <linux/list.h>

struct my_item {
    struct list_head list;  // Embed the list node
    int data;
};

struct list_head my_list;
INIT_LIST_HEAD(&my_list);

// Iterate safely
struct my_item *item;
list_for_each_entry(item, &my_list, list) {
    process(item->data);
}

// Single exit point with goto for cleanup
int complex_init(struct device *dev)
{
        int ret;

        dev->buffer = kmalloc(BUF_SIZE, GFP_KERNEL);
        if (!dev->buffer) {
                ret = -ENOMEM;
                goto err_buffer;
        }

        dev->workqueue = create_workqueue("mydev");
        if (!dev->workqueue) {
                ret = -ENOMEM;
                goto err_workqueue;
        }

        ret = register_device(dev);
        if (ret)
                goto err_register;

        return 0;

err_register:
        destroy_workqueue(dev->workqueue);
err_workqueue:
        kfree(dev->buffer);
err_buffer:
        return ret;
}

// Cleanup in reverse order of initialization
// One error path, easy to audit

subsystem: short summary (50 chars or less)

More detailed explanatory text, if necessary. Wrap it to about 72
characters. The blank line separating the summary from the body is
critical.

Explain the problem that this commit is solving. Focus on why you
are making this change as opposed to how. The code shows the how.

If there are any side effects or other unintuitive consequences of
this change, explain them here.

Fixes: abc123def456 ("commit that introduced bug")
Reported-by: Someone <someone@example.com>
Signed-off-by: Your Name <you@example.com>

// Branch prediction: common case first
if (likely(fast_path_condition)) {
    // Common case
    return quick_result;
}
// Slow path
return handle_slow_case();


// Cache-friendly iteration
// BAD: strided access
for (int i = 0; i < rows; i++)
    for (int j = 0; j < cols; j++)
        process(matrix[j][i]);  // Column-major = cache misses

// GOOD: sequential access
for (int i = 0; i < rows; i++)
    for (int j = 0; j < cols; j++)
        process(matrix[i][j]);  // Row-major = cache friendly


// Avoid unnecessary memory barriers
// Use READ_ONCE/WRITE_ONCE for shared data
int value = READ_ONCE(shared_variable);
WRITE_ONCE(shared_variable, new_value);

# Torvalds Git workflow

# Commit often, commit small
git add -p                    # Stage hunks, not files
git commit -m "subsystem: specific change"

# Rebase for clean history (before sharing)
git rebase -i HEAD~5          # Clean up local commits

# Never rebase published history
# History is sacred once pushed

# Bisect to find bugs
git bisect start
git bisect bad HEAD
git bisect good v5.10
# Git finds the breaking commit

# Blame to understand code
git blame -w -C -C file.c     # Ignore whitespace, track moves

// Define clear boundaries between subsystems
// Each subsystem has:
// 1. Public API (exported symbols)
// 2. Internal implementation
// 3. Data structures

// Public API
int subsystem_init(void);
void subsystem_cleanup(void);
int subsystem_do_thing(struct thing *t);

// Internal - not exported
static int internal_helper(void);
static struct cache internal_cache;

// Use proper namespacing
// subsystem_verb_noun()

int netdev_register_device(struct net_device *dev);
int netdev_unregister_device(struct net_device *dev);
int blkdev_read_sector(struct block_device *bdev, sector_t sector);

#include <linux/kref.h>

struct my_object {
    struct kref refcount;
    // ... other fields
};

static void my_object_release(struct kref *kref)
{
    struct my_object *obj = container_of(kref, struct my_object, refcount);
    kfree(obj);
}

// Get reference
struct my_object *my_object_get(struct my_object *obj)
{
    if (obj)
        kref_get(&obj->refcount);
    return obj;
}

// Release reference
void my_object_put(struct my_object *obj)
{
    if (obj)
        kref_put(&obj->refcount, my_object_release);
}