20070317 procfs slide


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20070317 procfs slide

  1. 1. Using and Programming Proc filesystem from internet ...
  2. 2. Content ● What's Procfs ● Basic useness of Procfs ● Programming Procfs ● Example source code ● Conclusion
  3. 3. What is Procfs ● In its simplest form procfs provides file-system abstraction for processes, presenting information about processes, their ex ecution environment, resource utilization etc. as files. ● The original design goal of procfs was to make debugger impl ementation easier. ● Systems like Linux have exposed a lot of other system interf aces and information through procfs ● There are Linux system utilities that essentially cat files in procfs!
  4. 4. What is Procfs (cont.) ● It is a virtual file system – Is a special file system in the linux kernel. – It exists only in memory. – Is a virtual file system that is not associated with a block device but exists only in memory. – allows programs in the user space to access to certain info rmation from the kernel.
  5. 5. What is Procfs (cont.) ● It is an abstraction allowing – access information on – configure the kernel ● It can be mounted by # mount -t proc proc /mnt Now procfs is mounted on /mnt, same to /proc
  6. 6. Basic useness of Procfs ● /proc/sys are sysctl files – They do not belong to procfs – Managed by different APIs ● Number named Dirs – PID as name – Appear and disappear as processes are created, finish
  7. 7. Basic useness of Procfs (cont.) ● Structure – cmdline : argument list, null-separated strings – cwd : symbolic link to the current working directory – environ : environment for the process – exe : a symbolic link containing the actual path name of the executed command – fd : a subdirectory containing one entry for each file which the process has open (file descriptor), a symbolic link to the actual file) – maps : currently mapped memory regions and their access permissions – root : points to the file system root, e.g / – stat : information about the process (used by ps) – statm : information about memory status in pages – status : much of the information in stat and statm in a more human readable/parsable format
  8. 8. Basic useness of Procfs (cont.) ● /proc/self: symbolic link to the current process ● /proc/cpuinfo: a collection of CPU and system architecture depen dent items, for each supported architecture a different list ● /proc/devices: listing of major numbers and device groups ● /proc/pci: listing of all PCI devices found during kernel i nitialization and their configuration (lspci command) ● /proc/tty/driver/serial: information on serial ports ● /proc/version: information on the kernel version – /proc/sys/kernel/ostype – /proc/sys/kernel/osrelease – /proc/sys/kernel/version
  9. 9. Basic useness of Procfs (cont.) ● /proc/sys/kernel/hostname: the name of the machine ● /proc/sys/kernel/domainname: the name of the domain ● /proc/meminfo: information on memory usage ● /proc/loadavg: load average numbers give information on the workload: – the number of jobs in the run queue (state R) or waiting for disk I/O (state D) averaged over 1, 5, and 15 minutes – PID of the last process being executed ● /proc/uptime: two pieces of information on the uptime of the system (seconds), and the amount of time spent in idle process (seconds) – Same information as uptime
  10. 10. Programming Procfs ● Program as kernel module ● #includeu <linux/proc_fs.h> ● struct proc_dir_entry* proc_mkdir (const char* name,struct proc_dir_entry* parent); ● struct proc_dir_entry* create_proc_entry (const char* name, mode_t mode,struct proc_dir_entry* parent); ● struct proc_dir_entry* proc_symlink (const char* name,struct proc_dir_entry* parent, const char *dest); ● void remove_proc_entry (const char *name, struct proc_dir_entry *parent);
  11. 11. Programming Procfs (cont.) ● procfs works with call back functionsfor files: functions that are called when a specific file is being read or written. ● Such functions have to be initialized by setting the file_operations member in the struct proc_dir_entry* that the function create_proc_entry returned. ● For read only proc file, call create_proc_read_entry is enough.
  12. 12. Programming Procfs (cont.) ● define read, write, open, release methods for your proc file see example source code. ● Original procfs can not pass data larger than 1 page. In order to pass large data, you should define a sequence method. ● Other detailed example, see the source code.
  13. 13. Example source code ● kernel module frame work. ● read the source code for each method of proc fs. ● build it ● insmod into kernel ● cd /proc, see /proc/foo and /proc/foo/foo ● try read/write permission ● be root user ● try read/write permission ● rmmod the kernel module
  14. 14. Conclusion ● Its candidate is sysfs. ● But Procfs is still very useful, because it is simple, and lot of legacy software need procfs.
  15. 15. Thank you ! Q & A