8 IPC.md

IPC

1) Pipe

pipe(): reader Descriptor, writer Descriptor

ialloc new inode
create file table entry for reader, writer point to inode
create descripter for reader, writer, point to file table entry
set inode reference count = 2
return reader,writer

• Each IPC contain
  • table ipc entry with key
  • status
  • permission
  • recycled
  • get
  • index = desc mod total entry

Messages:

• Messages as linked linked msg
• Message queue structure:
  • Total bytes on list
  • pointer to first and last message
  • maximum bytes
  • last process to send messages
  • time stamps of all operations

1. msgget(key,flag): descriptor

2) msgsnd(msg_descriptor, msg, count, flag):bytes sent

    check permissions
    while no space :
        if no wait flag:
            return
        sleep
    get a header
    copy data from user space to kernel
    modify ds:
            add header to queue
            header points data
            timestamps
            pid
    wake all process

3) msgrecv(msg_des, buffer, size_buffer, msg_type, flag):

    check permission
    loop:
        if type == 0:
            select first message
        if type>0:
            select first message with given type
        if type<0:
            select message less than abs(type)
        if theres a message:
            adjust message size
            if too small error
            copy text from kernel to user
            unlink message from queue
            return

4. msgctl(id,cmd,mstatbuf)