在Linux 2.6.33.6中，源文件在：/usr/src/kernels/2.6.33.6/include/linux/skbuff.h

struct sk_buff在2.6.18中的定义：

struct sk_buff {
        /* These two members must be first. */
        struct sk_buff          *next;
        struct sk_buff          *prev;

        struct sock             *sk;
        struct skb_timeval      tstamp;
        struct net_device       *dev;
        struct net_device       *input_dev;

        union {
                struct tcphdr   *th;
                struct udphdr   *uh;
                struct icmphdr  *icmph;
                struct igmphdr  *igmph;
                struct iphdr    *ipiph;
                struct ipv6hdr  *ipv6h;
                unsigned char   *raw;
        } h;

        union {
                struct iphdr    *iph;
                struct ipv6hdr  *ipv6h;
                struct arphdr   *arph;
                unsigned char   *raw;
        } nh;

        union {
                unsigned char   *raw;
        } mac;

        struct  dst_entry       *dst;
        struct  sec_path        *sp;
        /*
         * This is the control buffer. It is free to use for every
         * layer. Please put your private variables there. If you
         * want to keep them across layers you have to do a skb_clone()
         * first. This is owned by whoever has the skb queued ATM.
         */
        char                    cb[48];

        unsigned int            len,
                                data_len,
                                mac_len,
                                csum;
        __u32                   priority;
        __u8                    local_df:1,
                                cloned:1,
                                ip_summed:2,
                                nohdr:1,
                                nfctinfo:3;
        __u8                    pkt_type:3,
                                fclone:2,
#ifndef CONFIG_XEN
                                ipvs_property:1;
#else
                                ipvs_property:1,
                                proto_data_valid:1,
                                proto_csum_blank:1;
#endif
        __be16                  protocol;

        void                    (*destructor)(struct sk_buff *skb);
#ifdef CONFIG_NETFILTER
        struct nf_conntrack     *nfct;
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
       struct sk_buff          *nfct_reasm;
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
        struct nf_bridge_info   *nf_bridge;
#endif
        __u32                   nfmark;
#endif /* CONFIG_NETFILTER */
#ifdef CONFIG_NET_SCHED
        __u16                   tc_index;       /* traffic control index */
#ifdef CONFIG_NET_CLS_ACT
        __u16                   tc_verd;        /* traffic control verdict */
#endif
#endif
#ifdef CONFIG_NET_DMA
        dma_cookie_t            dma_cookie;
#endif
#ifdef CONFIG_NETWORK_SECMARK
        __u32                   secmark;
#endif

        /* These elements must be at the end, see alloc_skb() for details.  */
        unsigned int            truesize;
        atomic_t                users;
        unsigned char           *head,
                                *data,
                                *tail,
                                *end;
        /* Extra stuff at the end to avoid breaking abi */
#ifndef __GENKSYMS__
        int                      peeked;
#endif
};

struct sk_buff在2.6.33中的定义：

struct sk_buff {
        /* These two members must be first. */
        struct sk_buff          *next;
        struct sk_buff          *prev;

        ktime_t                 tstamp;

        struct sock             *sk;
        struct net_device       *dev;

        /*
         * This is the control buffer. It is free to use for every
         * layer. Please put your private variables there. If you
         * want to keep them across layers you have to do a skb_clone()
         * first. This is owned by whoever has the skb queued ATM.
         */
        char                    cb[48] __aligned(8);

        unsigned long           _skb_dst;
#ifdef CONFIG_XFRM
        struct  sec_path        *sp;
#endif
        unsigned int            len,
                                data_len;
        __u16                   mac_len,
                                hdr_len;
        union {
                __wsum          csum;
                struct {
                        __u16   csum_start;
                        __u16   csum_offset;
                };
        };
        __u32                   priority;
        kmemcheck_bitfield_begin(flags1);
        __u8                    local_df:1,
                                cloned:1,
                                ip_summed:2,
                                nohdr:1,
                                nfctinfo:3;
        __u8                    pkt_type:3,
                                fclone:2,
                                ipvs_property:1,
                                peeked:1,
                                nf_trace:1;
        __be16                  protocol:16;
        kmemcheck_bitfield_end(flags1);

        void                    (*destructor)(struct sk_buff *skb);
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
        struct nf_conntrack     *nfct;
        struct sk_buff          *nfct_reasm;
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
        struct nf_bridge_info   *nf_bridge;
#endif

        int                     skb_iif;
#ifdef CONFIG_NET_SCHED
        __u16                   tc_index;       /* traffic control index */
#ifdef CONFIG_NET_CLS_ACT
        __u16                   tc_verd;        /* traffic control verdict */
#endif
#endif

        kmemcheck_bitfield_begin(flags2);
        __u16                   queue_mapping:16;
#ifdef CONFIG_IPV6_NDISC_NODETYPE
        __u8                    ndisc_nodetype:2;
#endif
        kmemcheck_bitfield_end(flags2);

        /* 0/14 bit hole */

#ifdef CONFIG_NET_DMA
        dma_cookie_t            dma_cookie;
#endif
#ifdef CONFIG_NETWORK_SECMARK
        __u32                   secmark;
#endif
        union {
                __u32           mark;
                __u32           dropcount;
        };

        __u16                   vlan_tci;

        sk_buff_data_t          transport_header;
        sk_buff_data_t          network_header;
        sk_buff_data_t          mac_header;
        /* These elements must be at the end, see alloc_skb() for details.  */
        sk_buff_data_t          tail;
        sk_buff_data_t          end;
        unsigned char           *head,
                                *data;
        unsigned int            truesize;
        atomic_t                users;
};

有了以上定义的话，我们就可以做类似如下定义来使我们的驱动支持多内核了：

struct sk_buff *new_skb;
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
new_skb->mac.raw = (unsigned char *)new_eth_p;
#else
new_skb->mac_header = (unsigned char *)new_eth_p;
#endif

参考：http://www.linuxquestions.org/questions/linux-kernel-70/struct-sk_buff-differs-in-2-6-18-and-2-6-33-kernel-882507/

CentOS 上安装新版本 python

请看： 安装python以及解决版本问题

但在安装新版本后，yum不能正常使用了。原因是yum是基于默认的python版本运行的，例如CentOS6.2基于python2.6。但我们安装版本后建立了链接，覆盖掉了默认python调用，导致yum脚本无法正常调用到自己想要的版本。

解决方案

vim /usr/bin/yum

将第一行 #!/usr/bin/python 修改成 #!/usr/bin/python2.6

安装新版本python

wget http://python.org/ftp/python/2.7.3/Python-2.7.3.tar.bz2
tar xjf Python-2.7.3.tar.bz2
cd Python-2.7.3
./configure
make
make atlinstall

这时 python2.7.3 版本已经安装成功了。 但调用 python –version 依然会显示并使用旧版本

解决办法就是重新建立一个链接并覆盖掉旧的

ln -s /usr/local/bin/python2.7 /usr/bin/python -f

再调用 python –version 显示结果

[root@centos]# python --version
Python 2.7.3

至此，问题解决 :)

压缩

enData = zlib.compress(data)[2:-4]

对应：

compress2(dstbuf, &dstLen, strSrc, srcLen, 6);

解压

deData = zlib.decompress(enData, -zlib.MAX_WBITS)

对应：

bool gzipInflate( const std::string& compressedBytes, std::string& uncompressedBytes ) {
    if ( compressedBytes.size() == 0 ) {
        uncompressedBytes = compressedBytes ;
        return true ;
    }

    uncompressedBytes.clear() ;

    unsigned full_length = compressedBytes.size() ;
    unsigned half_length = compressedBytes.size() / 2;

    unsigned uncompLength = full_length ;
    char* uncomp = (char*) calloc( sizeof(char), uncompLength );

    z_stream strm;
    strm.next_in = (Bytef *) compressedBytes.c_str();
    strm.avail_in = compressedBytes.size() ;
    strm.total_out = 0;
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;

    bool done = false ;

    //if (inflateInit2(&strm, (16+MAX_WBITS)) != Z_OK)
    if (inflateInit2(&strm, -MAX_WBITS) != Z_OK)
    {
        free( uncomp );
        return false;
    }

    while (!done) {
        // If our output buffer is too small
        if (strm.total_out >= uncompLength ) {
            // Increase size of output buffer
            char* uncomp2 = (char*) calloc( sizeof(char), uncompLength + half_length );
            memcpy( uncomp2, uncomp, uncompLength );
            uncompLength += half_length ;
            free( uncomp );
            uncomp = uncomp2 ;
        }

        strm.next_out = (Bytef *) (uncomp + strm.total_out);
        strm.avail_out = uncompLength - strm.total_out;

        // Inflate another chunk.
        int err = inflate (&strm, Z_SYNC_FLUSH);
        if (err == Z_STREAM_END) done = true;
        else if (err != Z_OK)  {
            break;
        }
    }

    if (inflateEnd (&strm) != Z_OK) {
        free( uncomp );
        return false;
    }

    for ( size_t i=0; i<strm.total_out; ++i ) {
        uncompressedBytes += uncomp[ i ];
    }
    free( uncomp );
    return true ;
}

Linux使用gcc编译使用zlib库的代码时，使用 -lz 来链接(link) zlib 库。

否则就会出现类似 undefined reference to `deflateInit_’ 的错误

当调用tcpdump时，出现错误：tcpdump: USB link-layer type filtering not implemented

原因

说明系统可能有多块网卡共存。

需要指定工作网卡才能开始截包，使用参数举例

[root@centos]# tcpdump -i eth0 udp port 53

在实际使用中例子中“eth0”“udp”“53”等参数，要根据实际需要来进行修改。 虽然一般单网卡默认名称应该是eth0，但也有其他情况。实际中要使用ifconfig查看自己需要使用的网卡。

错误原因

我手上一个项目本身采用gcc编译。后来因为代码功能需要移植到g++中时，出现了 “inet_addr” was not declared in this scope 这个错误。

解决方案

// 添加该头文件
#include <arpa/inet.h>

如果出现下面错误：

error: string: No such file or directory
error: vector: No such file or directory
  • 说明在将g++项目用gcc编译
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