Sdp: fixed unbalanced paren

2012-10-25T23:20:22Z

fixed unbalanced paren

← Older revision		Revision as of 23:20, 25 October 2012
Line 73:		Line 73:
	Row 6: Minor Number.		Row 6: Minor Number.

	Every driver may control different hardware controllers. These controllers are assigned major numbers. Each device they control is assigned a minor number. Any device can be identified with a major minor number pair. (see [http://uw714doc.sco.com/en/HDK_concepts/ddT_majmin.html ~~HKD~~]		Every driver may control different hardware controllers. These controllers are assigned major numbers. Each device they control is assigned a minor number. Any device can be identified with a major minor number pair. (see [http://uw714doc.sco.com/en/HDK_concepts/ddT_majmin.html SCO documentation for major and minor numbers])

	* d = directory		* d = directory

Cdelahou: added major minor number

2012-10-25T22:45:13Z

added major minor number

← Older revision		Revision as of 22:45, 25 October 2012
Line 18:		Line 18:
	Filesystems		Filesystems
	* blocks -> actual data		* blocks -> actual data
	* inodes -> metadata (index node). 2 Types:		* inodes -> metadata (index node).

			2 Types of inode:
	** directories and files are inodes		** directories and files are inodes
	** directory inode -> name to inode mapping		** directory inode -> name to inode mapping
Line 67:		Line 69:



			Row 5: Major Number.
			Row 6: Minor Number.

			Every driver may control different hardware controllers. These controllers are assigned major numbers. Each device they control is assigned a minor number. Any device can be identified with a major minor number pair. (see [http://uw714doc.sco.com/en/HDK_concepts/ddT_majmin.html HKD]

	* d = directory		* d = directory

Cdelahou: added notes

2012-10-25T05:14:42Z

added notes

Show changes

Cdelahou: added notes

2012-10-25T04:57:09Z

added notes

New page

##Linux source code spelunking ( see linux source cross reference)
* /documention
* /arch --> platform specific code
* /drives --> drivers for devices
* /fs -> file system stuff (ext4 is here... open.c)

do\_ prefix on something is a wrapper function that preprocesses args

#####Looking at fs/ directory now...
All these help with the vfs
Relationship between dentry (directory entry) and inode
Contents are inodes, dentry is a string representingo

dentry, inode

Looding at struct dentry
locks --> spin lock, spinning --> locks file by constantly looping over it

###Filesystems
* blocks -> actual data
* inodes -> metadata (index done)
** directories and files are inodes
** directory inode -> name to inode mapping
** file inode -> size, last modified, pointers to data blocks, permissions, etc...
*** pointers to data wihtin inodes tell you where the data is, so that you can access
it

How to explore the kernel from userspace instead of messing about in the source code.

Look at the output of $>mount
* some kernerl services are mounted to various folders (proc mounted to /proc)

in /dev/, do $> ls -l
drwxr-xr-x 2 root root 700 Oct 5 22:23 block
drwxr-xr-x 2 root root 120 Oct 5 22:23 bsg
brw-rw---- 1 root disk 7, 7 Oct 5 22:23 loop7
crw------- 1 root root 10, 237 Oct 5 22:23 loop-control
drwxr-xr-x 2 root root 80 Oct 5 22:23 mapper
crw------- 1 root root 10, 227 Oct 5 22:23 mcelog
crw-r--r-- 1 root root 10, 62 Oct 5 22:23 rfkill
lrwxrwxrwx 1 root root 4 Oct 5 22:23 rtc -> rtc0
crw------- 1 root root 254, 0 Oct 5 22:23 rtc0
brw-rw---- 1 root disk 8, 0 Oct 5 22:23 sda
brw-rw---- 1 root disk 8, 1 Oct 5 22:23 sda1
brw-rw---- 1 root disk 8, 2 Oct 5 22:23 sda2
crw-rw---- 1 root disk 21, 2 Oct 5 22:23 sg2
crw------- 1 root root 21, 3 Oct 5 22:23 sg3
lrwxrwxrwx 1 root root 8 Oct 5 22:23 shm -> /run/shm
crw------- 1 root root 10, 231 Oct 5 22:23 snapshot
drwxr-xr-x 3 root root 180 Oct 5 22:23 snd
lrwxrwxrwx 1 root root 15 Oct 5 22:23 stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root root 15 Oct 5 22:23 stdout -> /proc/self/fd/1
crw-rw-rw- 1 root tty 5, 0 Oct 17 08:47 tty
crw--w---- 1 root tty 4, 0 Oct 5 22:23 tty0
crw------- 1 root root 252, 5 Oct 5 22:23 usbmon5
drwxr-xr-x 4 root root 80 Oct 5 22:23 v4l
crw-rw---- 1 root tty 7, 0 Oct 5 22:23 vcs
crw-rw-rw- 1 root root 1, 5 Oct 5 22:23 zero

major minor numbers? row 5, row 6 <--- LOOOK UP!

/dev is dynamically generated by udev

d = directory
b = block device --> drives, etc.
c = character file --> write or output sequences of characters (printers, zero, null)

random, urandom, null, zero are all device files, but they're really just special
function in the kernel. They use the FILE api, you can read and write to most of
them.

in /dev. run $>df .

Filesystem 1K-blocks Used Available Use% Mounted on
udev 499124 8 499116 1% /dev

The file system for this is udev, dyamically generated

udev rules are set in /etc/udev, sets who can access what devices. Sets policy.
see man udev
what is udevd vs udev?
* udev is filesystem type and a command
* udevd is a daemon that monitors changes

If you kill udevd, your kernel will not be informed of new changes (plugged in
devices). They won't be listed in /dev/.
The user cannot be informed of what is actually mounted.

LOOK UP udevd

initrd has it's own /dev/ folder to allow SPECIAL devices to be mounted to before the file
system and the root /dev/ is loaded

DEV IS defined in posix standard

Kernel state is defined as special files too! We don't need need special functions,
just look at the files in /proc/
* all numbers are process IDs
* other devices like uptime

Ownership, groups, 'n stuff are all displayed in the files

NOTICE that all of the sizes of these files are 0.

When you call $> ps, all it's doing is calling walking the proc directory.

Proc is NOT defined in the POSIX standard. It's a linux thing.

/sys/ and /proc/ are basically the same thing, but /sys is alot more regimented, proc
is loose. <---- LOOOOOOK UP!

Ex:
$> strace ifconfig
You'll notice that much of what ifconfig does is reading kernel /proc/ files

NOTE: /dev/ -> devices
/proc/ and /sys/ -> KERNEL STATE

LINKS

Hardlink --> associate between name and inode. Can have many per inode.

ex:
ls -l /bin | grep gunzip
-rwxr-xr-x 2 root root 2251 Feb 8 2012 gunzip
Two links to gunzip's inode. Meaning, uncompress points to the same inode
gunzip and uncompress binaries have the same inode

Symlink: pointer to a name, not an inode. You can have pointer to a name that's a
has a hardlink to an actual piece of data

COMP 3000 2012 Week 7 Notes - Revision history

Sdp: fixed unbalanced paren

Cdelahou: added major minor number

Cdelahou: added notes

Cdelahou: added notes