Question

我正在使用内核3.13.0编写Linux设备驱动程序，而且我很困惑为什么我会收到此警告。

warning: initialization from incompatible pointer type [enabled by default]
     .read = read_proc,
     ^
warning: (near initialization for ‘proc_fops.read’) [enabled by default]

据我所知，我的file_operations设置proc函数与设备函数相同。我可以读/写/ dev / MyDevice没有问题，也没有警告。 proc写入函数不会发出警告，只会读取。我做错了什么？

/*****************************************************************************/
//DEVICE OPERATIONS
/*****************************************************************************/ 
static ssize_t dev_read(struct file *pfil, char __user *pBuf, size_t
  len, loff_t *p_off)
{
    //Not relevant to this question
}

static ssize_t dev_write(struct file *pfil, const char __user *pBuf,
                         size_t len, loff_t *p_off)
{
    //Not relevant to this question
}

static struct file_operations dev_fops =
{ //None of these cause a warning but the code is identical the proc code below
    .owner = THIS_MODULE,
    .read = dev_read,
    .write = dev_write
};

/*****************************************************************************/
//PROCESS OPERATIONS
/*****************************************************************************/
static int read_proc(struct file *pfil, char __user *pBuf, size_t
              len, loff_t *p_off)
{
    //Not relevant to this question
}

static ssize_t write_proc(struct file *pfil, const char __user *pBuf,
                         size_t len, loff_t *p_off)
{
    //Not relevant to this question
}

struct file_operations proc_fops = 
{
    .owner = THIS_MODULE,
    .write = write_proc,
    .read = read_proc, //This line causes the warning.
};

编辑：所以答案是，我是一个因为没有看到＆＃34; int＆＃34;与＆＃34; ssize_t＆＃34;。谢谢大家！ Codenheim和Andrew Medico几乎在同一时间得到了正确答案，但我之所以选择Medico，是因为它对未来的访客更为迂腐和明显。

Answer 1

read_proc函数的返回类型（抛出警告）与编译干净的函数不匹配。

static ssize_t dev_read(struct file *pfil, char __user *pBuf, size_t len, loff_t *p_off)

VS

static int read_proc(struct file *pfil, char __user *pBuf, size_t len, loff_t *p_off)

ssize_t和int的大小可能不同。您的函数的返回类型应为ssize_t。

Answer 2

使用文件操作时，只需按照此结构遵循规则

struct file_operations {
    struct module *owner;
    loff_t (*llseek) (struct file *, loff_t, int);
    ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
    ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
    ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
    ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
    ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
    ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
    int (*iterate) (struct file *, struct dir_context *);
    unsigned int (*poll) (struct file *, struct poll_table_struct *);
    long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
    long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
    int (*mmap) (struct file *, struct vm_area_struct *);
    int (*open) (struct inode *, struct file *);
    int (*flush) (struct file *);
    int (*release) (struct inode *, struct file *);
    int (*fsync) (struct file *, loff_t, loff_t, int datasync);
    int (*aio_fsync) (struct kiocb *, int datasync);
    int (*fasync) (int, struct file *, int);
    int (*lock) (struct file *, int, struct file_lock *);
    ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
    unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
    int (*check_flags)(int);
    int (*flock) (struct file *, int, struct file_lock *);
    ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, size_t, unsigned int);
    ssize_t (*splice_read)(struct file *, struct pipe_inode_info *, size_t, unsigned int);
    int (*setlease)(struct file *, long arg, struct file_lock **);
    long (*fallocate)(struct file *, int mode, loff_t offset, loff_t len);
    int (*show_fdinfo)(struct seq_file *m, struct file *f); };

您可以在Kernel Documentation Documentation / filesystems / vfs.txt中找到此结构，或者您可以使用来自Kernel Source的标记vim -t file_operations找到它，或者您可以查看头文件/include/linux/fs.h.

只是你的错误是返回类型你使用静态int而不是使用ssize_t。

Answer 3

函数指针需要一个返回类型为ssize_t的函数，但是你给它一个int

您需要ssize_t，而不是int。

为什么存在不兼容的指针类型警告？

3 个答案: