linux-ext4 - Re: ext2_block_alloc

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Date:	Tue, 23 Dec 2008 10:30:21 +0530
From:	"Manish Katiyar" <mkatiyar@...il.com>
To:	"Peter Teoh" <htmldeveloper@...il.com>
Cc:	"Mike Snitzer" <snitzer@...il.com>,
	"Rohit Sharma" <imreckless@...il.com>,
	Kernelnewbies <kernelnewbies@...linux.org>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: ext2_block_alloc_info

On Tue, Dec 23, 2008 at 9:59 AM, Peter Teoh <htmldeveloper@...il.com> wrote:
> Sorry, resent due to SMTP error:
>
> anyone knows any way of enumerating all the low level information like
> these for each file?
>
> Best I can get is "debugfs":
>
> So using "show_inode_infor xxxx":
>
> Inode: 1146884   Type: regular    Mode:  0767   Flags: 0x0
> Generation: 4262211373
> User:     0   Group:     0   Size: 4670783
> File ACL: 0    Directory ACL: 0
> Links: 1   Blockcount: 9152
> Fragment:  Address: 0    Number: 0    Size: 0
> ctime: 0x46db7fb6 -- Mon Sep  3 11:29:58 2007
> atime: 0x47c66735 -- Thu Feb 28 15:48:05 2008
> mtime: 0x43118298 -- Sun Aug 28 17:23:36 2005
> BLOCKS:
> (0-11):2317946-0, (IND):2317958, (12-1035):2317959-0, (DIND):2318983,
> (IND):2318984, (1036-1140):2318985-0
> TOTAL: 1144
>
> Here the "BLOCKS" correspond to the block numbering we are talking
> about, right?   It always start at 0 per-file.   "IND" is the indirect
> block.
>  But what is "DIND"?

Double indirect blocks ..... Sine the size of file is 4670783, we
would need 1140 direct blocks (holding data) and other indirect
blocks.

>  "2317946" is the physical block number
> right?
Yes.......

> And what is the zero after the "2317946"?
0 is just the end specifier for a range which debugfs prints. So
either you print the range of blocks or a 0 at the end to mark the
start of a new range. The code to do is present in
e2fsprogs/debugfs/debugfs.c : list_blocks_proc()

list_block_proc () {
...................
	/*
	 * Not a normal block.  Always force a new range.
	 */
	finish_range(lb);
	if (lb->first)
		lb->first = 0;
	else
		fprintf(lb->f, ", ");
	if (blockcnt == -1)
		fprintf(lb->f, "(IND):%u", *blocknr);
	else if (blockcnt == -2)
		fprintf(lb->f, "(DIND):%u", *blocknr);
	else if (blockcnt == -3)
		fprintf(lb->f, "(TIND):%u", *blocknr);
...................
}


Thanks -
Manish


>
> On Tue, Dec 23, 2008 at 10:56 AM, Mike Snitzer <snitzer@...il.com> wrote:
>>
>> On Sat, Dec 20, 2008 at 8:25 PM, Peter Teoh <htmldeveloper@...il.com> wrote:
>> > On Sat, Dec 20, 2008 at 11:43 PM, Rohit Sharma <imreckless@...il.com> wrote:
>> >> A little confusion.
>> >>
>> >> Just refer this structure in linux/ext2_fs_sb.h
>> >>
>> >> struct ext2_block_alloc_info {
>> >>  46        /* information about reservation window */
>> >>  47        struct ext2_reserve_window_node rsv_window_node;
>> >>  48        /*
>> >>  49         * was i_next_alloc_block in ext2_inode_info
>> >>  50         * is the logical (file-relative) number of the
>> >>  51         * most-recently-allocated block in this file.
>> >>  52         * We use this for detecting linearly ascending allocation requests.
>> >>  53         */
>> >>  54        __u32                   last_alloc_logical_block;
>> >
>> > if i interpret the meaning of "file-relative logical number"
>> > correctly, and since one-file-one-inode concept, then it means that it
>> > should mean inode-relative logical block number.
>> >
>> >>  55        /*
>> >>  56         * Was i_next_alloc_goal in ext2_inode_info
>> >>  57         * is the *physical* companion to i_next_alloc_block.
>> >>  58         * it the the physical block number of the block which was
>> >
>> >> inode1 has logical blocks 0 1 2 , physical 22 23 24
>> >> inode2 has logical blocks 0 1 2 , physical 34 35 50
>> >>
>> >
>> > as per comment above, the sequence above looks likely, but then this
>> > is my guess again.
>>
>> You are correct.  last_alloc_logical_block is used to detect if the
>> write workload against a given inode is sequential (the current
>> logical block is last_alloc_logical_block+1).
>>
>> Mike
>
>
>
> --
> Regards,
> Peter Teoh
>
> Ernest Hemingway - "Never mistake motion for action."
> --
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