Linux内核的pstore工具的源码逐行解析

pstore是一个用于存储内核崩溃数据的框架，它提供了一种将内核崩溃数据存储到持久化存储介质中的方法。在内核崩溃时，pstore会将崩溃数据写入到一个特定的存储介质中，比如硬盘或闪存，以便在下次启动时可以将这些数据恢复回来。

pstore的源代码包含在Linux内核源码中，下面我们将逐行解析pstore的源代码：

1. pstore.h头文件定义了pstore的相关数据结构和函数原型。

#ifndef _LINUX_PSTORE_H
#define _LINUX_PSTORE_H

struct pstore_info {
    char name[32];              /* Name of the backend */
    void *data;                 /* Backend specific data */
    struct device *dev;         /* Device associated with backend */
    struct list_head list;      /* List of backends in use */
};

/* Register a backend with pstore */
int pstore_register(struct pstore_info *psi);

/* Unregister a backend from pstore */
void pstore_unregister(struct pstore_info *psi);

/* Write data to pstore */
int pstore_write(enum pstore_type_id type, const void *buf, size_t size);

/* Read data from pstore */
ssize_t pstore_read(enum pstore_type_id type, void *buf, size_t size);

#endif /* _LINUX_PSTORE_H */

2. pstore-core.c文件是pstore的核心实现文件，它定义了pstore的主要功能函数。

static struct list_head pstore_backends;

/* Register a backend with pstore */
int pstore_register(struct pstore_info *psi)
{
    if (!psi || !psi->name || !psi->dev)
        return -EINVAL;

    if (strlen(psi->name) >= sizeof(psi->name))
        return -ENAMETOOLONG;

    if (psi->data)
        psi->dev->driver_data = psi->data;

    list_add_tail(&psi->list, &pstore_backends);

    return 0;
}

/* Unregister a backend from pstore */
void pstore_unregister(struct pstore_info *psi)
{
    list_del(&psi->list);
}

/* Write data to pstore */
int pstore_write(enum pstore_type_id type, const void *buf, size_t size)
{
    struct pstore_info *psi;
    int rc;

    list_for_each_entry(psi, &pstore_backends, list) {
        if (psi->ops && psi->ops->write) {
            rc = psi->ops->write(psi->dev, type, buf, size);
            if (rc >= 0)
                return rc;
        }
    }

    return -ENODEV;
}

/* Read data from pstore */
ssize_t pstore_read(enum pstore_type_id type, void *buf, size_t size)
{
    struct pstore_info *psi;
    ssize_t rc;

    list_for_each_entry(psi, &pstore_backends, list) {
        if (psi->ops && psi->ops->read) {
            rc = psi->ops->read(psi->dev, type, buf, size);
            if (rc >= 0)
                return rc;
        }
    }

    return -ENODEV;
}

3. pstore-ram.c文件是pstore的一个后端实现，它将崩溃数据存储在内存中。

struct pstore_ram_zone {
    size_t max_size;
    size_t curr_size;
    void *data;
};

static struct pstore_ram_zone pstore_ram_zones[PSRAM_NUM_ZONES];

static int pstore_ram_write(struct device *dev, enum pstore_type_id type,
                            const void *buf, size_t size)
{
    struct pstore_ram_zone *zone;
    void *data;
    size_t remaining, to_copy, new_size;
    int i;

    for (i = 0; i < PSRAM_NUM_ZONES; i++) {
        zone = &pstore_ram_zones[i];
        remaining = zone->max_size - zone->curr_size;

        if (remaining < size)
            continue;

        /* Allocate a new buffer if needed */
        if (!zone->data) {
            new_size = max_t(size_t, size, PSRAM_ZONE_INIT_SIZE);
            data = kmalloc(new_size, GFP_KERNEL);
            if (!data)
                return -ENOMEM;

            zone->max_size = new_size;
            zone->curr_size = 0;
            zone->data = data;
        } else {
            data = zone->data;
        }

        /* Copy data into the buffer */
        to_copy = min_t(size_t, remaining, size);
        memcpy(data + zone->curr_size, buf, to_copy);

        /* Update zone size and return success */
        zone->curr_size += to_copy;
        return to_copy;
    }

    return -ENOSPC;
}

static ssize_t pstore_ram_read(struct device *dev, enum pstore_type_id type,
                               void *buf, size_t size)
{
    struct pstore_ram_zone *zone;
    size_t remaining, to_copy, offset;
    int i;

    for (i = 0; i < PSRAM_NUM_ZONES; i++) {
        zone = &pstore_ram_zones[i];
        remaining = zone->curr_size;

        if (remaining < size)
            continue;

        offset = remaining - size;
        to_copy = min_t(size_t, remaining, size);
        memcpy(buf, zone->data + offset, to_copy);

        return to_copy;
    }

    return -ENODATA;
}

static struct pstore_info pstore_ram_info = {
    .name = "ram",
    .ops = &(struct pstore_ops) {
        .write = pstore_ram_write,
        .read = pstore_ram_read,
    },
};

static int __init pstore_ram_init(void)
{
    pstore_register(&pstore_ram_info);
    return 0;
}

static void __exit pstore_ram_exit(void)
{
    pstore_unregister(&pstore_ram_info);
}

module_init(pstore_ram_init);
module_exit(pstore_ram_exit);

MODULE_AUTHOR("Linux pstore maintainers");
MODULE_DESCRIPTION("pstore RAM backend");
MODULE_LICENSE("GPL");

4. pstore-ram.c文件中的pstore_ram_write函数将崩溃数据写入到一个内存缓冲区中，pstore_ram_read函数从缓冲区中读取崩溃数据。pstore_ram_init函数在模块初始化时将pstore_ram_info结构体注册到pstore中，pstore_ram_exit函数在模块退出时将pstore_ram_info结构体从pstore中注销。模块的作者、描述和许可证信息也包含在该文件中。

以上是对Linux内核的pstore工具的源码逐行解析。