The structure of the Reiser file system
A key {a, b, 0, 0} will always yield the stat item of the directory or file, and subsequent items will follow immediately after that in the file system tree. The stat item contains the size of the actual item in bytes. With this information and using the size information of the individual item headers, the keys for other parts of the directory/file can be constructed and the parts located. In many cases, the items will be arranged consecutively on the disk, anyway.
The following three examples will show three different types of files: a very small file consisting only of a stat item and a tail, a larger file that actually has an indirect item, and finally a very large file that spans over multiple indirect items. We again use the example partition from above, which is an image of a partition mounted as "/var" in a SuSe Linux 8.0 system.
Example 1: small file The first example is that of a small file that contains only of a stat item and one direct item. The file is "/var/log/y2start.log-initial". The root directory ("/var") has key {1,2,0,0}, which by navigating the file system tree can be found in block 8416. There we can find that the "log" directory has key {2,13,0,0}. This directory is also contained in block 8416. The file "y2start.log-initial" has key {13, 1633, 0, 0}. By inspecting block 8482, we find that this key is contained in the leaf node block number 24224. The item headers for the keys {13, 1633, 0, 0} and {13, 1633, 1, 2} are as follows: 00000090 0d 00 00 00 61 06 00 00 00 00 00 00 00 00 00 00 ....a...........
000000a0 ff ff 2c 00 a4 0b 01 00 0d 00 00 00 61 06 00 00 ÿÿ,.¤.......a...
000000b0 01 00 00 00 00 00 00 20 ff ff f0 00 b4 0a 01 00 ....... ÿÿð.´...
Key: {13, 1633, 0, 0}
Count: 0xffff
Length: 44 bytes
Location: byte 2980 (0xba4)
Version: 1 (new)
Key: {13, 1633, 1, 2}
Count: 0xffff
Length: 240 bytes
Location: byte 2740 (0xab4)
Version: 1 (new)
At byte 2740 (0xab4) in the block, we find the direct item for the file followed by the stat item at byte 2980 (0xba4): 00000ab0 65 6e 76 0a 65 63 68 6f 20 59 32 44 env.echo Y2D
00000ac0 45 42 55 47 20 28 29 0a 6d 65 6d 69 6e 66 6f 20 EBUG ().meminfo
00000ad0 31 20 3d 20 4d 65 6d 3a 20 31 30 33 33 34 35 36 1 = Mem: 1033456
00000ae0 20 38 35 39 37 36 20 39 34 37 34 38 30 20 30 20 85976 947480 0
00000af0 36 34 32 34 20 35 37 31 37 32 0a 69 53 65 72 69 6424 57172.iSeri
00000b00 65 73 3d 31 0a 68 76 63 5f 63 6f 6e 73 6f 6c 65 es=1.hvc_console
00000b10 3d 31 0a 58 31 31 69 3d 0a 4d 65 6d 54 6f 74 61 =1.X11i=.MemTota
00000b20 6c 3d 31 30 33 33 34 35 36 0a 66 62 64 65 76 5f l=1033456.fbdev_
00000b30 6f 6b 3d 31 0a 75 70 64 61 74 65 3d 0a 58 56 65 ok=1.update=.XVe
00000b40 72 73 69 6f 6e 3d 34 0a 58 53 65 72 76 65 72 3d rsion=4.XServer=
00000b50 66 62 64 65 76 0a 78 73 72 76 3d 58 46 72 65 65 fbdev.xsrv=XFree
00000b60 38 36 0a 73 63 72 65 65 6e 3d 66 62 64 65 76 0a 86.screen=fbdev.
00000b70 6d 65 6d 69 6e 66 6f 20 32 20 3d 20 4d 65 6d 3a meminfo 2 = Mem:
00000b80 20 31 30 33 33 34 35 36 20 39 32 34 30 34 20 39 1033456 92404 9
00000b90 34 31 30 35 32 20 30 20 38 32 33 32 20 36 30 35 41052 0 8232 605
00000ba0 31 36 0a 00 a4 81 05 00 01 00 00 00 ef 00 00 00 16..¤.......ï...
00000bb0 00 00 00 00 00 00 00 00 00 00 00 00 25 15 3e 3d ............%.>=
00000bc0 25 15 3e 3d 25 15 3e 3d 08 00 00 00 d5 02 00 00 %.>=%.>=....Õ...
|
