linux-ext4 - Re: ext2_block_alloc

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Message-ID: <804dabb00812222029x76d34c24o798ade5dd0e31351@mail.gmail.com>
Date:	Tue, 23 Dec 2008 12:29:46 +0800
From:	"Peter Teoh" <htmldeveloper@...il.com>
To:	"Mike Snitzer" <snitzer@...il.com>
Cc:	"Rohit Sharma" <imreckless@...il.com>,
	Kernelnewbies <kernelnewbies@...linux.org>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: ext2_block_alloc_info

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"?   "2317946" is the physical block number
right?   And what is the zero after the "2317946"?

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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