Mastering Linux Kernel Development

Data structures

Each message queue is created by enumerating a set of data structures by the underlying SysV IPC subsystem. struct msg_queue is the core data structure, and an instance of this is enumerated for each message queue:

struct msg_queue {        struct kern_ipc_perm q_perm;        time_t q_stime; /* last msgsnd time */        time_t q_rtime; /* last msgrcv time */        time_t q_ctime; /* last change time */        unsigned long q_cbytes; /* current number of bytes on queue */        unsigned long q_qnum; /* number of messages in queue */        unsigned long q_qbytes; /* max number of bytes on queue */        pid_t q_lspid; /* pid of last msgsnd */        pid_t q_lrpid; /* last receive pid */       struct list_head q_messages; /* message list */ struct list_head q_receivers;/* reader process list ...