ceph主要数据结构解析2-Rados.h文件
（1）文件系统id结构：16个字符组成struct ceph_fsid {
unsigned char fsid;
};
以及对应的比较函数：
static inline int ceph_fsid_compare(const struct ceph_fsid *a,
const struct ceph_fsid *b)
{
return memcmp(a, b, sizeof(*a));
}
（2）定义保留的snap的id宏
typedef __le64 ceph_snapid_t;
#define CEPH_SNAPDIR ((__u64)(-1))/* reserved for hidden .snap dir */
#define CEPH_NOSNAP((__u64)(-2))/* "head", "live" revision */
#define CEPH_MAXSNAP ((__u64)(-3))/* largest valid snapid */
struct ceph_timespec {//自定义的时间描述结构体
__le32 tv_sec;
__le32 tv_nsec;
} __attribute__ ((packed));
（3）对象布局宏：对象怎样放到放置组PG里面去（placement group）
#define CEPH_OBJECT_LAYOUT_HASH 1 //哈希
#define CEPH_OBJECT_LAYOUT_LINEAR 2 //线性
#define CEPH_OBJECT_LAYOUT_HASHINO3 //哈希inode
struct ceph_object_layout {//对象布局
struct ceph_pg ol_pgid; /* raw pg, with _full_ ps precision. */
__le32 ol_stripe_unit; /* for per-object parity, if any */
} __attribute__ ((packed));
（4）PG布局宏：PG怎样放置到存储设备上去
#define CEPH_PG_LAYOUT_CRUSH0 //CRUSH算法，伪随机hash
#define CEPH_PG_LAYOUT_HASH 1 //hash
#define CEPH_PG_LAYOUT_LINEAR 2 //线性
#define CEPH_PG_LAYOUT_HYBRID 3
#define CEPH_PG_MAX_SIZE 16/* max # osds in a single pg */
（5）PG编码到一个64位
struct ceph_pg {
__le16 preferred; /* preferred primary osd */参考主osd
__le16 ps; /* placement seed */放置种子
__le32 pool; /* object pool */对象池
} __attribute__ ((packed));
下面是两种对象池的宏定义：
#define CEPH_PG_TYPE_REP 1 //冗余
#define CEPH_PG_TYPE_RAID4 2 //raid
控制PG数量的函数定义：保证b小于bmask并且bmask是2的n次方的最小值
随着时间b的增加产生一个稳定的映射
static inline int ceph_stable_mod(int x, int b, int bmask)
{
if ((x & bmask) < b)
return x & bmask;
else
return x & (bmask >> 1);
}
（6）划时代和版本的组合，被用作存储层的序列化突变
struct ceph_eversion {
__le32 epoch;
__le64 version;
} __attribute__ ((packed));
（7）osd（对象存储设备）映射位的宏定义：
#define CEPH_OSD_EXISTS(1<<0) //osd存在
#define CEPH_OSD_UP (1<<1) //
#define CEPH_OSD_AUTOOUT (1<<2)/* osd was automatically marked out */自动标出
#define CEPH_OSD_NEW (1<<3)/* osd is new, never marked in */新的，从未标记
extern const char *ceph_osd_state_name(int s);//得到对应的名字，实现如下：
const char *ceph_osd_state_name(int s)
{
switch (s) {
case CEPH_OSD_EXISTS:
return "exists";
case CEPH_OSD_UP:
return "up";
case CEPH_OSD_AUTOOUT:
return "autoout";
case CEPH_OSD_NEW:
return "new";
default:
return "???";
}
}
/* osd weights.fixed point value: 0x10000 == 1.0 ("in"), 0 == "out" */
osd的权重值：最大为0x10000相当于1.0，最小为0
#define CEPH_OSD_IN0x10000
#define CEPH_OSD_OUT 0
（8）osd映射标志位定义：
#define CEPH_OSDMAP_NEARFULL (1<<0)/* sync writes (near ENOSPC) */
#define CEPH_OSDMAP_FULL (1<<1)/* no data writes (ENOSPC) */
#define CEPH_OSDMAP_PAUSERD(1<<2)/* pause all reads */暂停所有读
#define CEPH_OSDMAP_PAUSEWR(1<<3)/* pause all writes */
#define CEPH_OSDMAP_PAUSEREC (1<<4)/* pause recovery */
/*
* The error code to return when an OSD can't handle a write
* because it is too large.
*/因为数据太大导致OSD不能处理些时返回的错误代码
#define OSD_WRITETOOBIG EMSGSIZE
（9）osd的操作
#define CEPH_OSD_OP_MODE 0xf000 //操作模式
#define CEPH_OSD_OP_MODE_RD 0x1000 //读
#define CEPH_OSD_OP_MODE_WR 0x2000 //写
#define CEPH_OSD_OP_MODE_RMW 0x3000 //读修改写
#define CEPH_OSD_OP_MODE_SUB 0x4000 //子操作
#define CEPH_OSD_OP_TYPE 0x0f00 //操作类型
#define CEPH_OSD_OP_TYPE_LOCK0x0100//锁
#define CEPH_OSD_OP_TYPE_DATA0x0200 //数据
#define CEPH_OSD_OP_TYPE_ATTR0x0300 //属性
#define CEPH_OSD_OP_TYPE_EXEC0x0400 //执行
#define CEPH_OSD_OP_TYPE_PG 0x0500 //PG
#define CEPH_OSD_OP_TYPE_MULTI 0x0600 /* multiobject */多对象
下面是定义操作模式与类型组合的枚举：
enum {
CEPH_OSD_OP_READ = CEPH_OSD_OP_MODE_RD | CEPH_OSD_OP_TYPE_DATA | 1,
中间省略很多...
CEPH_OSD_OP_PGLS_FILTER = CEPH_OSD_OP_MODE_RD | CEPH_OSD_OP_TYPE_PG | 2,
};
以及定义了判断操作是否为每一种类型或模式的操作，如判断是否为锁操作类型的函数如下：
static inline int ceph_osd_op_type_lock(int op)
{
return (op & CEPH_OSD_OP_TYPE) == CEPH_OSD_OP_TYPE_LOCK;
}
返回操作名称的函数：
extern const char *ceph_osd_op_name(int op);
（10）osd操作标志定义：有详细的英文注释了
enum {
CEPH_OSD_FLAG_ACK = 0x0001,/* want (or is) "ack" ack */
CEPH_OSD_FLAG_ONNVRAM = 0x0002,/* want (or is) "onnvram" ack */
CEPH_OSD_FLAG_ONDISK = 0x0004,/* want (or is) "ondisk" ack */
CEPH_OSD_FLAG_RETRY = 0x0008,/* resend attempt */
CEPH_OSD_FLAG_READ = 0x0010,/* op may read */
CEPH_OSD_FLAG_WRITE = 0x0020,/* op may write */
CEPH_OSD_FLAG_ORDERSNAP = 0x0040,/* EOLDSNAP if snapc is out of order */
CEPH_OSD_FLAG_PEERSTAT_OLD = 0x0080,/* DEPRECATED msg includes osd_peer_stat */
CEPH_OSD_FLAG_BALANCE_READS =0x0100,
CEPH_OSD_FLAG_PARALLELEXEC = 0x0200,/* execute op in parallel */
CEPH_OSD_FLAG_PGOP = 0x0400,/* pg op, no object */
CEPH_OSD_FLAG_EXEC = 0x0800,/* op may exec */
CEPH_OSD_FLAG_EXEC_PUBLIC = 0x1000,/* op may exec (public) */
CEPH_OSD_FLAG_LOCALIZE_READS = 0x2000,/* read from nearby replica, if any */
CEPH_OSD_FLAG_RWORDERED = 0x4000,/* order wrt concurrent reads */
};
enum {
CEPH_OSD_OP_FLAG_EXCL = 1, /* EXCL object create */
CEPH_OSD_OP_FLAG_FAILOK = 2, /* continue despite failure */
};
#define EOLDSNAPC 85/* ORDERSNAP flag set; writer has old snapc*/
#define EBLACKLISTED 108 /* blacklisted */
（11）扩展属性比较操作枚举定义：
enum {
CEPH_OSD_CMPXATTR_OP_NOP = 0,
CEPH_OSD_CMPXATTR_OP_EQ= 1,
CEPH_OSD_CMPXATTR_OP_NE= 2,
CEPH_OSD_CMPXATTR_OP_GT= 3,
CEPH_OSD_CMPXATTR_OP_GTE = 4,
CEPH_OSD_CMPXATTR_OP_LT= 5,
CEPH_OSD_CMPXATTR_OP_LTE = 6
};
enum {
CEPH_OSD_CMPXATTR_MODE_STRING = 1,
CEPH_OSD_CMPXATTR_MODE_U64 = 2
};
（12）osd操作结构体封装定义，可能是来至数据有效负载：
struct ceph_osd_op {
__le16 op; /* CEPH_OSD_OP_* */
__le32 flags; /* CEPH_OSD_FLAG_* */
union {//各种数据包格式定义
struct {
__le64 offset, length;//偏移量和长度
__le64 truncate_size;
__le32 truncate_seq;
} __attribute__ ((packed)) extent;
struct {
__le32 name_len;
__le32 value_len;
__u8 cmp_op; /* CEPH_OSD_CMPXATTR_OP_* */
__u8 cmp_mode; /* CEPH_OSD_CMPXATTR_MODE_* */
} __attribute__ ((packed)) xattr;
struct {
__u8 class_len;
__u8 method_len;
__u8 argc;
__le32 indata_len;
} __attribute__ ((packed)) cls;
struct {
__le64 count;
__le32 start_epoch; /* for the pgls sequence */
} __attribute__ ((packed)) pgls;
struct {
__le64 snapid;
} __attribute__ ((packed)) snap;
struct {
__le64 cookie;
__le64 ver;
__u8 flag;/* 0 = unwatch, 1 = watch */
} __attribute__ ((packed)) watch;
struct {
__le64 offset, length;
__le64 src_offset;
} __attribute__ ((packed)) clonerange;
};
__le32 payload_len;//数据长度
} __attribute__ ((packed));
struct ceph_osd_reply_head {//回复头部
__le32 client_inc; /* client incarnation */
__le32 flags;
struct ceph_object_layout layout;
__le32 osdmap_epoch;
struct ceph_eversion reassert_version; /* for replaying uncommitted */
__le32 result; /* result code */
__le32 object_len; /* length of object name */
__le32 num_ops; //操作数量
struct ceph_osd_op ops;/* ops[], object */存放所有操作
} __attribute__ ((packed));
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