c - 如何填写用于 msghdr 的 iov_iter 结构？

Question

我正在尝试使用 sock_sendmsg() 从驱动程序发送 UDP 数据包。

关于如何使用 sock_sendmsg() 和 msghdr 填充 UDP 数据包并传输它有几个指南，但它们都是针对旧内核版本的。在 3.13 和 4.8 之间的某个时间，struct msghdr 更改为:

struct msghdr {
    void    *   msg_name;   /* Socket name          */
    int     msg_namelen;    /* Length of name       */
    struct iovec *  msg_iov;    /* Data blocks          */
    __kernel_size_t msg_iovlen; /* Number of blocks     */
    void    *   msg_control;    /* Per protocol magic (eg BSD file descriptor passing) */
    __kernel_size_t msg_controllen; /* Length of cmsg list */
    unsigned int    msg_flags;
};

收件人:

struct msghdr {
    void        *msg_name;  /* ptr to socket address structure */
    int     msg_namelen;    /* size of socket address structure */
    struct iov_iter msg_iter;   /* data */
    void        *msg_control;   /* ancillary data */
    __kernel_size_t msg_controllen; /* ancillary data buffer length */
    unsigned int    msg_flags;  /* flags on received message */
    struct kiocb    *msg_iocb;  /* ptr to iocb for async requests */
};

不是将 msg_iov 设置为指向带有数据的 iovec:

struct msghdr msg = {};
struct iovec iov = {}; 

iov.iov_base = data;
iov.iov_len = dataLen;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;

现在有一个 iov_iter 结构:

struct iov_iter {
    int type;
    size_t iov_offset;
    size_t count;
    union {
        const struct iovec *iov;
        const struct kvec *kvec;
        const struct bio_vec *bvec;
        struct pipe_inode_info *pipe;
    };
    union {
        unsigned long nr_segs;
        struct {
            int idx;
            int start_idx;
        };
    };
};

如何用数据填充 msghdr 中的 iov_iter 结构，以便将其传递给 sock_sendmsg？

Answer 1

在尝试并阅读 Ctx ( lwn.net/Articles/625077 ) 发布的指南后，我明白了。

unsigned long nr_segments = 1;
size_t count = 1;
struct msghdr msg = {};
struct iovec iov = {}; 

iov.iov_base = data;
iov.iov_len = dataLen;

iov_iter_init(&msg.msg_iter, READ, &iov, nr_segments, count);