feat(dns) 实现 DNS 解析事件的捕获

[Ghostbaby]

功能：

• 完整 ebpf example dns failure 的代码的移植
• 完成多内核的适配

[Ghostbaby]

struct iov_iter 内存布局发生变化
内核 4.19

struct iov_iter {
        unsigned int               type;                 /*     0     4 */

        /* XXX 4 bytes hole, try to pack */

        size_t                     iov_offset;           /*     8     8 */
        size_t                     count;                /*    16     8 */ 
        union {                    
                const struct iovec  * iov;               /*    24     8 */
                const struct kvec  * kvec;               /*    24     8 */
                const struct bio_vec  * bvec;            /*    24     8 */
                struct pipe_inode_info * pipe;           /*    24     8 */
        };                                               /*    24     8 */
        union {
                long unsigned int  nr_segs;              /*    32     8 */
                struct {
                        int        idx;                  /*    32     4 */
                        int        start_idx;            /*    36     4 */
                };                                       /*    32     8 */
        };                                               /*    32     8 */

        /* size: 40, cachelines: 1, members: 5 */
        /* sum members: 36, holes: 1, sum holes: 4 */
        /* last cacheline: 40 bytes */
};

内核 5.10

struct iov_iter {
        u8                         iter_type;            /*     0     1 */
        bool                       nofault;              /*     1     1 */
        bool                       data_source;          /*     2     1 */

        /* XXX 5 bytes hole, try to pack */

        size_t                     iov_offset;           /*     8     8 */
        size_t                     count;                /*    16     8 */
        union {
                const struct iovec  * iov;               /*    24     8 */
                const struct kvec  * kvec;               /*    24     8 */
                const struct bio_vec  * bvec;            /*    24     8 */
                struct xarray *    xarray;               /*    24     8 */
                struct pipe_inode_info * pipe;           /*    24     8 */
        };                                               /*    24     8 */
        union {
                long unsigned int  nr_segs;              /*    32     8 */
                struct {
                        unsigned int head;               /*    32     4 */
                        unsigned int start_head;         /*    36     4 */
                };                                       /*    32     8 */
                loff_t             xarray_start;         /*    32     8 */
        };                                               /*    32     8 */

        /* size: 40, cachelines: 1, members: 7 */
        /* sum members: 35, holes: 1, sum holes: 5 */
        /* last cacheline: 40 bytes */
};

内核 6.8

struct iov_iter {
        u8                         iter_type;            /*     0     1 */
        bool                       nofault;              /*     1     1 */
        bool                       data_source;          /*     2     1 */

        /* XXX 5 bytes hole, try to pack */

        size_t                     iov_offset;           /*     8     8 */
        union {
                struct iovec       __ubuf_iovec;         /*    16    16 */
                struct {
                        union {    
                                const struct iovec  * __iov; /*    16     8 */
                                const struct kvec  * kvec; /*    16     8 */
                                const struct bio_vec  * bvec; /*    16     8 */
                                struct xarray * xarray;  /*    16     8 */
                                void * ubuf;             /*    16     8 */
                        };                               /*    16     8 */
                        size_t     count;                /*    24     8 */
                };                                       /*    16    16 */
        };                                               /*    16    16 */
        union {
                long unsigned int  nr_segs;              /*    32     8 */
                loff_t             xarray_start;         /*    32     8 */
        };                                               /*    32     8 */

        /* size: 40, cachelines: 1, members: 6 */
        /* sum members: 35, holes: 1, sum holes: 5 */
        /* last cacheline: 40 bytes */
};

问题

1. 通过 iov_iter.iov 获取 DNS 解析的数据，在6.8内核需要处理不兼容的字段。

方案

1. 参考Handling incompatible field and type changes 章节解决不兼容字段的问题

struct task_struct___old {
    long state;
} __attribute__((preserve_access_index));