why sector number not match block number?

why sector number not match block number?

[Sucan Zhang]

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Hi,

i want to get the exact match between block number and sector number of a
file in domU. so i do follows .


root@feisty:~# ls -l
total 1
-rw-r--r-- 1 root root 4 Jun  9 08:16 a

root@feisty:~# filefrag -v a
Checking a
Filesystem type is: ef53
Filesystem cylinder groups is approximately 122
Blocksize of file a is 1024
File size of a is 2 (1 blocks)
First block: 247208
Last block: 247208
a: 1 extent found

the file has one block and block size is 247208, so the secoter size is
247208 *2 +1 == 78B51 and 247208*2 +2 == 78B52    (block number count begin
from 0 , sector number count begin from 1).

root@feisty:~# echo "a" >> a

command above is a write to a file

root@feisty:~# tail /var/log/messages
Jun  9 08:15:54 feisty kernel: do_blk_req cf9d1de8: cmd cf9d1e64, sec ae85e,
(2/2) buffer:cf7a1800 [write]
Jun  9 08:16:14 feisty kernel: do_blk_req cf9d152c: cmd cf9d15a8, sec ae7c6,
(2/2) buffer:ce81ec00 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d152c: cmd cf9d15a8, sec 2,
(2/2) buffer:d06ee400 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d1f40: cmd cf9d1fbc, sec 6,
(2/2) buffer:d06eec00 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d1e94: cmd cf9d1f10, sec 880d0,
(2/2) buffer:d0392000 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d1de8: cmd cf9d1e64, sec 880d4,
(2/2) buffer:d0392800 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d11d0: cmd cf9d124c, sec 880d8,
(2/2) buffer:cecdf000 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d127c: cmd cf9d12f8, sec ac002,
(2/2) buffer:cf1e4400 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d1124: cmd cf9d11a0, sec ae25a,
(2/2) buffer:cf652400 [write]
Jun  9 08:16:19 feisty kernel: do_blk_req cf9d1b38: cmd cf9d1bb4, sec ae67c,
(2/2) buffer:ce6d1800 [write]

and then to show sector number i had written, i expect to see 78B51 or 78B52
sector number. but none of then display, can you tell me why?

-- 
Regards,
Sucan

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Re: why sector number not match block number?

[John Haxby]

Sucan Zhang wrote:
> and then to show sector number i had written, i expect to see 78B51 or 
> 78B52 sector number. but none of then display, can you tell me why?

I believe you need to add the offset of the partition in which the file 
is located.   If you're using LVM then you'll also need to go through 
the physical extent mapping shown by lvdisplay -m.

jch