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> 1. P.15 Chapter 2 - Process Management
> 1. Process include :
> 1. text section: executing program code
> 2. data section: global variables, a set of resources
> such as open files, pending signals, an address space
> 3. one or more threads of execution
> 2. Each thread includes a unique program counter, process
> stack, and set of processor registers, but linux does not
> differentiate between threads and processes.
> 3. Processes provide two vitualizations:
> 1. virtualized proessor : sharing the processor among
> dozens of other processes
> 2. virtual memory : it lets the process allocate and
> manage memory as if it alone owned all the memory in
> the system.
> 4. When a process exits, it is placed into a special zombie
> state that is used to represent terminated processes until
> the parent calls wait() or waitpid()
> 5. The kernel representation of a running program as a task,
> and the user-space representation as a process.
> 2. P.16 The Process Descriptor and Task Structure
> 1. The kernel stores the processes in a circular doubly
> linked list called the task list.
> 2. The process descriptor contains the data that describe the
> executing program: running state, open files, the
> process's address space, pending signals, permission,
> semaphore, executing time...
> 3. The task_struct is allocated via the slab allocator to
> provide object reuse and cache coloring.
> 4. Prior to the 2.6 kernel series, the task_struct was stored
> at the end of the kernel stack of each process. This
> allowed architectures with few registers, such as x86, to
> calculate the location of the process descriptor via the
> stack pointer without using an extra register to store the
> location.
> 3. P.18 Storing the Process Descriptor
> 1. The system identifies processes by a unique PID. The
> default maximum value is 32767(up to 4294967296).
> 2. It is very useful to be able to quickly lookup the process
> descriptor of the currently executing task, which is done
> via the current macro. This macro must be separately
> implemented by each supported architecture.
> 4. P.19 Process states:
> 1. The state field of the process descriptor describes the
> current condition of the process. The value is represented
> by one of five flags:
> 1. TASK_RUNNING: it is either currently running or on a
> runqueue waiting to run (runqueue are discussed in
> Chap. 3).
> 2. TASK_INTERRUPTIBLE: it is sleeping, blocked, waiting
> for some condition to occur. When this condition
> occurs, the kernel sets the process's state to
> TASK_RUNNING. The processes also awakes prematurely
> and becomes runnable if it receives a signal.
> 3. TASK_UNINTERRUPTIBLE: it will not wake up and become
> runnable if it receives a signal. (see fork())
> 4. TASK_ZOMBIE: The task has terminated, but its parent
> has not yet issued a wait4() system call. The task's
> process descriptor must remain in case the parent
> wants to access it.
> 5. TASK_STOPPED: This occurs if the task receives the
> SIGSTOP, SIGTSTP, SIGTTIN, or SIGTTOU signal or if
> it receives any signal while it is being debugged.
>
> --- refer ---
>
> 1. running: on user space.
> 2. interrupt routine: a exception handler such as KBD,
> timer.
> 3. system call: such as read, write.
> 4. waiting: wait for an event.
> 5. return: kernel will check scheduler, signals.
> 6. ready: ready to run.
>
> interrupt (kernel) scheduler
> ----------.--------------------------------.--------------
> . .
> . .
> running ===+==> system call <==================> waiting
> ^ . | | . ^
> | . | | . |
> | . |=====|=> interrupt routing <==========+
> | . | | .
> | . | | .
> | . v v .
> +-----.----- return <=======================> ready
> . .
> . .
>
>
> 5. P.20 Manipulating the Current Process State
> 1. Using the set_task_state(task, state) function to set the
> given task to the given state.
> 6. P.20 Process Context
> 1. One of the most important parts of a process is the
> executing program code.
> 2. When a program executes a system call or triggers an
> exception, it enters kernel-space. At this point, the
> kernel is said to "be executing on behalf of the process"
> and is in process context.
> 3. When in process context, the current macro is valid.
> 4. All processes are descendents of the init process whose
> PID is 1.
> 5. Every process on the system has exactly one parent.
> Likewise, every process can have one or more children. The
> relationship between processes is stored in the process
> descriptor.
>
># pstree
> init-+-apache--5*[apache]
> |-apmd
> |-atd
> |-bash-+-bash--Xprt
> | |-logger
> | `-tee
> |-bdflush
> |-brltty
> |-cron
> |-5*[getty]
> |-inetd
> |-kapmd
> |-keventd
> |-khubd
> |-kjournald
> |-klogd
> |-kreiserfsd
> |-ksoftirqd_CPU0
> |-kswapd
> |-kupdated
> `-syslogd
>
>
> 7. P.22 Process Creation
> 1. fork() : creates a child process that is a copy of the
> current task. It differs from the parent only in its PID,
> its PPID, and certain resources and statistics, such as
> pending signals, which are not inherited.
> 2. exec() : loads a new executable into the address space and
> begins executing it.
> 3. With Linux, fork() is implemented using copy-on-write
> pages. Instead of duplicating the process address space,
> the parent and the child can share a single copy. The data
> is marked in such a way that if it is written to, a
> duplicate is made and each process receives a unique copy.
> 4. If exec() is called immediately after fork() - they never
> need to be copied. The only overhead incurred by fork() is
> the duplication of the parent's page tables and the
> creation of a unique process descriptor for the child.
> 8. P.23 fork()
> 1. fork() <-- clone() <-- do_fork() <-- copy_process()
> 1. Calls dup_task_struct() which creates a new kernel
> stack, thread_info structure, and task_struct for
> the new process whose values are identical to those
> of the current task.
> 2. Check that the new child will not exceed the
> resource limits on the number of processes for the
> current user.
> 3. Now the child needs to differentiate itself from its
> parent. Various members of the process descriptor
> are cleared or set to initail values.
> 4. Next, the child's state is set to
> TASK_UNINTERRUPTIBLE, to insure it does not yet run.
> 5. Calls copy_flags() to update the flags member of the
> task_struct. The PF_SUPERPRIV flag, which denotes
> whether a task used super-user priv, is cleared. The
> PF_FORKNOEXEC flag, which denotes a process that has
> not called exec(), is set.
> 6. Calls get_pid() to assign an available PID to the
> new task.
> 7. Depending on the flags passed to clone(), either
> copy or share open files, filesystem information,
> signal handlers, process address space, and namespace.
> 8. Share the remaining timeslice between the parent and
> its child.
> 9. Cleanup and return a pointer to the new child.
> 2. ==> The kernel runs the child process first. (avoid
> copy-on-write overhead)
> 9. P.24 vfork()
> 1. The vfork() has the same effect as fork(), except that the
> page table entries of the parent process are not copied.
> Instead, the child executes as the sole thread in the
> parent's address space, and the parent is blocked until
> the child either calls exec() or exits.
> 2. The child is not allowed to write to the address space.
> 3. ==> use fork() is ok in kernel > 2.2.
> 10. P.25 The Linux Implementation of Threads
> 1. The Linux kernel done not provide any special scheduling
> semantics or data structures to represent threads.
> Instead, a thread is merely a process which share certain
> resources. Each thread has a unique task_struct and
> appears to the kernel as a normal process which shares the
> address space, filesystem resources, file descriptors, and
> installed signal handlers.
> 2. Threads are created like normal task with the exception
> that the clone() system call is passed flags corresponding
> to specific resources to be shared:
> clone (CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND, 0);
> fork() can be implemented by clone() as:
> clone (SIGCHLD, 0);
> vfork() as:
> clone (CLONE_VFORK | CLONE_VM | SIGCHLD, 0);
>
>- clone() Flags:
>
> Flag Meaning
> ============== ======================================================
> CLONE_CLEARTID clear the TID
> CLONE_DETACHED the parent does not want a SIGCHLD signal send on exit
> CLONE_FILES parent and child share open files
> CLONE_FS parent and child share filesystem information
> CLONE_IDLETASK set PID to zero (only used by the idle tasks)
> CLONE_NEWNS create a new namespace for the child
> CLONE_PARENT child is to have same parent as its parent
> CLONE_PTRACE continue tracing child
> CLONE_SETTID write the PID back to user-space
> CLONE_SETTLS create a new TLS for the child
> CLONE_SIGHAND parent and child share signal handlers
> CLONE_SYSVSEM parent and child share System V SEM_UNDO semantics
> CLONE_THREAD parent and child aew in the same thread group
> CLONE_VFORK vfork() was used and the parent will sleep until the
> child wakes it
> CLONE_VM parent and child share address space
> ============== ======================================================
>
>
> 11. P.26 Kernel Threads
> 1. Kernel Threads is often useful for the kernel to perform
> some operations in the background -- standard processes
> that exist solely in kernel space.
> 2. The significant difference between kernel threads and
> normal processes is that kernel threads do not have an
> address space and do not context switch into user-space.
> Kernel threads are schedulable and preemptable as normal
> processes.
> 3.
>
> # ps axw
> PID TTY STAT TIME COMMAND
> 1 ? S 0:05 init [5]
> 2 ? SW 0:00 [keventd]
> 0 ? SWN 0:00 [ksoftirqd_CPU0]
> 0 ? SW 0:11 [kswapd]
> 0 ? SW 0:00 [bdflush]
> 0 ? SW 0:00 [kupdated]
> 7 ? SW 0:00 [khubd]
> 8 ? SW 1:45 [kjournald]
> 60 ? SW 0:00 [kapmd]
>
>
> 4. Indeed, a kernel thread can only be created by another
> kernel thread. The interface for spawning a new kernel
> thread from an existing one is: int kernel_thread (int
> (*fn)(void *), void * arg, unsigned long flags) flags:
> most kernel threads pass CLONE_FS | CLONE_FILES |
> CLONE_SIGHAND
> 12. P.27 Process Termination
> 1. Typically, processes destruction occurs when the process
> calls the exit() system call: exit() or return from main().
> 2. A process can also terminate when it receives a signal or
> exception it cannot handle or ignore.
> 3. do_exit() in kernel complete a number of chores(in
> kernel/exit.c):
> 1. Set the PF_EXITING flag in the flags member of the
> task_struct.
> 2. If BSD process accounting is enabled, call
> acct_process() to write out accounting information.
> 3. Call __exit__mm() to release the mm_struct held by
> this process.
> 4. Call sem_exit(). Dequeue its IPC semaphor if it
> queued waiting for.
> 5. Call __exit_files(), __exit_fs(), exit_namespace(),
> and exit_sighand() to decrement the usage count of
> objects related to file descriptors, filesystem
> data, the process namespace, and signal handlers,
> respectively.
> 6. Set the task's exit code, stored in the exit_code
> member of the task_struct, to the code provided by
> exit() or whatever kernel mechanism forced the
> termination.
> 7. Call exit_notify() to send signals to the task's
> parent, reparent any of the task's children to
> another thread in their thread group or the init
> process, and set the task's state to TASK_ZOMBIE.
> 8. Finally, call schedule() to switch to a new process,
> this is the last code the task will ever execute.
> 9. ==> The only memory it occupies is its kernel stack
> and slab object, which contain its thread_info and
> task_struct structures. The task exists solely to
> provide information to its parent.
> 13. P.28 Removal of the Process Descriptor
> 1. The acts of cleaning up after a process and removing its
> process descriptor are separate.
> 2. When it is time to finally deallocate the process
> descriptor, release_task() is invoked. It does the following:
> 1. Call free_uid() to decrement the usage count of the
> process's user.
> 2. Call unhash_process() to remove the process from the
> pidhash and remove the process from the task list.
> 3. If the task was ptraced, reparent it to its original
> parent and remove it from the ptrace list.
> 4. Call put_task_struct() to free the pages containing
> the process's kernel stack and thread_info structure
> and deallocate the slab cache containing the
> task_struct.
> 14. P.28 The Dilemma of the Parentless Task
> 1. http://www.qnx.com/developers/docs/qnx_4.25_docs/qnx4/sysarch/proc.html
>
> 2. The solution, hinted upon previously, is to reparent a
> task's children on exit to either another process in the
> current thread group or, if that fails, the init process.
>
> 1. Commands for Process
> Command Description
> ps report a snapshot of the current processes.
> top display Linux tasks
> nice run a program with modified scheduling priority
> renice alter priority of running processes
> kill
> send a signal to a process Name Num Action Description
> 0 0 n/a exit code indicates if a signal may be sent
> ALRM 14 exit
> HUP 1 exit
> INT 2 exit
> KILL 9 exit this signal may not be blocked
> PIPE 13 exit
> POLL exit
> PROF exit
> TERM 15 exit
> USR1 exit
> USR2 exit
> VTALRM exit
> STKFLT exit may not be implemented
> PWR ignore may exit on some systems
> WINCH ignore
> CHLD ignore
> URG ignore
>
> killall kill processes by name
> skill, snice send a signal or report process status
> pstree display a tree of processes
> pgrep, pkill look up or signal processes based on name and
> other attributes
> free Display amount of free and used memory in the system
> uptime Tell how long the system has been running.
> w Show who is logged on and what they are doing.
> pidof find the process ID of a running program.
> fuser identify processes using files or sockets
> sleep, usleep delay for a specified amount of time
> time counting running time of a command
> jobs show stopped processes list
> history command history
> nohup run a command immune to hangups, with output to a non-tty
> at, batch, atq, atrm queue, examine or delete jobs for later
> execution
> crontab maintain crontab files for individual users
> bg, fg let stopped process run on background, foreground
> procinfo display system status gathered from /proc
> reboot, halt, shutdown, poweroff stop the system
>
> 2. /proc
> 1. apm: advanced power manager
> 1.16 1.2 0x03 0x01 0xff 0x80 -1% -1 ?
> 2. bus: such pci, usb bus.
> 3. cmdline: boot parameter for kernel
> root=/dev/hda4 vga=785 rootfstype=ext3
> 4. cpuinfo
> attribute value
> processor 0
> vendor_id GenuineIntel
> cpu family 6
> model 7
> model name Pentium III (Katmai)
> stepping 3
> cpu MHz 451.028
> cache size 512 KB
> fdiv_bug no
> hlt_bug no
> f00f_bug no
> coma_bug no
> fpu yes
> fpu_exception yes
> cpuid level 2
> wp yes
> flags fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca
> cmov pat pse36 mmx fxsr sse
> bogomips 897.84
>
> 5. devices
> * Character devices:
> Major Number Device Name
> 1 mem
> 2 pty
> 3 ttyp
> 4 ttyS
> 5 cua
> 7 vcs
> 10 misc
> 14 sound
> 29 fb
> 81 video_capture
> 108 ppp
> 128 ptm
> 136 pts
> 162 raw
> 180 usb
>
> * Block devices:
> Major Number Device Name
> 2 fd
> 3 ide0
> 7 loop
> 114 ataraid
>
> 6. dma
> 7. driver
> 8. execdomains
> 9. fb
> 10. filesystems
> /dev node? filesystem
> nodev rootfs
> nodev bdev
> nodev proc
> nodev sockfs
> nodev tmpfs
> nodev shm
> nodev pipefs
> ext3
> ext2
> nodev ramfs
> iso9660
> nodev devpts
> nodev usbdevfs
> nodev usbfs
> nodev autofs
> nodev nfs
> vfat
> reiserfs
>
> 11. fs
> 12. ide
> 13. interrupts
> IRQ Number in CPU0 ??? Name
> 0 20684227 XT-PIC timer
> 1 74567 XT-PIC keyboard
> 2 0 XT-PIC cascade
> 4 153184 XT-PIC serial
> 8 4 XT-PIC rtc
> 10 0 XT-PIC usb-uhci, ESS Solo1
> 11 4078280 XT-PIC eth0
> 12 301378 XT-PIC PS/2 Mouse
> 14 1182857 XT-PIC ide0
> NMI 0
> ERR 0
>
> 14. iomem
> Address Description
> 00000000-0009fbff System RAM
> 0009fc00-0009ffff reserved
> 000a0000-000bffff Video RAM area
> 000c0000-000c7fff Video ROM
> 000f0000-000fffff System ROM
> 00100000-07ffcfff System RAM
> 00100000-00245388 Kernel code
> 00245389-002d0c03 Kernel data
> 07ffd000-07ffefff ACPI Tables
> 07fff000-07ffffff ACPI Non-volatile Storage
> e1000000-e100007f 3Com Corporation 3c905B 100BaseTX
> [Cyclone]
> e1800000-e3dfffff PCI Bus #01
> ?1800000-e1800fff ATI Technologies Inc 3D Rage Pro AGP 1X/2X
> ?2000000-e2ffffff ATI Technologies Inc 3D Rage Pro AGP 1X/2X
> ?2000000-e212bfff vesafb
> e3f00000-e3ffffff PCI Bus #01
> e4000000-e7ffffff Intel Corp. 440BX/ZX/DX - 82443BX/ZX/DX
> Host bridge
> ffff0000-ffffffff reserved
>
> 15. ioports
> IO-Address Description
> 0000-001f dma1
> 0020-003f pic1
> 0040-005f timer
> 0060-006f keyboard
> 0070-007f rtc
> 0080-008f dma page reg
> 00a0-00bf pic2
> 00c0-00df dma2
> 00f0-00ff fpu
> 01f0-01f7 ide0
> 02f8-02ff serial(set)
> 03c0-03df vesafb
> 03f6-03f6 ide0
> 03f8-03ff serial(set)
> 0cf8-0cff PCI conf1
> 9400-947f 3Com Corporation 3c905B 100BaseTX [Cyclone]
> 9400-947f 00:0c.0
> 9800-9803 ESS Technology ES1969 Solo-1 Audiodrive
> 9800-9803 ESS Solo1
> a000-a003 ESS Technology ES1969 Solo-1 Audiodrive
> ?000-a003 ESS Solo1
> a400-a40f ESS Technology ES1969 Solo-1 Audiodrive
> ?400-a40f ESS Solo1
> a800-a80f ESS Technology ES1969 Solo-1 Audiodrive
> ?804-a80f ESS Solo1
> b000-b03f ESS Technology ES1969 Solo-1 Audiodrive
> ?000-b00f ESS Solo1
> b400-b41f Intel Corp. 82371AB/EB/MB PIIX4 USB
> ?400-b41f usb-uhci
> b800-b80f Intel Corp. 82371AB/EB/MB PIIX4 IDE
> ?800-b807 ide0
> ?808-b80f ide1
> d000-dfff PCI Bus #01
> ?800-d8ff ATI Technologies Inc 3D Rage Pro AGP 1X/2X
> e400-e43f Intel Corp. 82371AB/EB/MB PIIX4 ACPI
> e800-e81f Intel Corp. 82371AB/EB/MB PIIX4 ACPI
>
> 16. irq
> 17. kcore
> 18. kmsg
> 19. ksyms : refer to System.map after build kernel source
> 20. loadavg : refer to "uptime" command
> 21. locks
> 22. meminfo : refer to "free", "top" command
> 23. misc
> 24. modules : modules in kernel : build in + insmod
> 25. mounts : refer to "mount", normally ln -s /proc/mounts
> /etc/mtab
> 26. mtrr
> 27. net
> 28. partitions : refer to "fdisk -l"
> major minor #blocks name
> 3 0 19551168 hda
> 3 1 4192933 hda1
> 3 2 88357 hda2
> 3 3 249007 hda3
> 3 4 15020775 hda4
>
> 29. pci
> 30. scsi
> 31. self : "self" process, symbolic to /proc/#PID
> 32. slabinfo
> 33. stat : cpu, swap, interrupt, diskio, boot time
> 34. swaps :
>
>Filename Type Size Used Priority
>/dev/hda3 partition 248996 26540 -1
>
>
> 35. sys
> 36. sysvipc : IPC
> 37. tty
> 38. uptime
> 39. version : refer to "uname -a" command
> 40. video
>
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