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12-30-2009, 10:00 AM
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#1
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LQ Newbie
Registered: May 2009
Location: Bangalore, India
Distribution: Kubuntu 2.6.31-14
Posts: 19
Rep: 
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Why do inode numbers start from 1 and not 0 ?
The C language convention counts array indices from 0. Why do inode numbers start from 1 and not 0 ?
I am currently reading "The design of the Unix Operating System" by Maurice J Bach and was struck on this question from the exercises.
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12-30-2009, 10:50 AM
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#2
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Guru
Registered: Mar 2004
Distribution: SusE 8.2
Posts: 5,861
Rep: 
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Hint: what's the value of "null"?
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12-30-2009, 11:00 AM
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#3
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LQ Veteran
Registered: Nov 2005
Location: Annapolis, MD
Distribution: Arch/XFCE
Posts: 17,797
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Quote:
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Why do inode numbers start from 1 and not 0 ?
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Why should they start with 0?
Quote:
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The C language convention counts array indices from 0.
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So what?
Why does GRUB count from 0?
Why does hard disk device numbering start with "a" and "1"?
Seriously---there are many kinds of computer utilities and conventions--there is no standard that says that numbering should start with 0 or 1. Unfortunately, you simply have to remember what convetion is followed for each situation. |
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12-30-2009, 12:16 PM
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#4
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Member
Registered: Sep 2007
Location: Mariposa
Distribution: Debian lenny, Slackware 12
Posts: 806
Rep:
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Quote:
Originally Posted by pixellany
Why does GRUB count from 0?
Why does hard disk device numbering start with "a" and "1"?
Seriously---there are many kinds of computer utilities and conventions
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Correct. But it's interesting to note that if you use inode=0 to mean that we're not referencing an inode (yet), that makes it easy to initialize a directory block: just smear it with 0x00 bytes. |
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12-31-2009, 03:04 PM
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#5
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Senior Member
Registered: Feb 2004
Location: SE Tennessee, USA
Distribution: Gentoo, LFS
Posts: 4,554
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Throughout the "C" world, an all-zero value is used to indicate "nothing." For instance, a value of zero in some inode-number slot would indicate that there is no inode associated with that slot.
Many Linux and Unix systems actually use inode numbers now that are random.
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12-31-2009, 08:03 PM
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#6
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Member
Registered: Sep 2007
Location: Mariposa
Distribution: Debian lenny, Slackware 12
Posts: 806
Rep:
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Quote:
Originally Posted by sundialsvcs
Many Linux and Unix systems actually use inode numbers now that are random.
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Citation needed. |
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12-31-2009, 09:20 PM
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#7
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LQ Veteran
Registered: Nov 2005
Location: Annapolis, MD
Distribution: Arch/XFCE
Posts: 17,797
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Quote:
Originally Posted by wje_lq
Citation needed.
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Why? (We're not writing peer-reviewed papers here......  ) |
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01-01-2010, 12:24 AM
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#8
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Member
Registered: Sep 2007
Location: Mariposa
Distribution: Debian lenny, Slackware 12
Posts: 806
Rep:
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Quote:
Originally Posted by pixellany
Why? (We're not writing peer-reviewed papers here...... ) |
Not to prove the point, but to provide more information. I'd like to read about this random inode number assignment idea in more detail. Why would they do this? (for example) |
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01-01-2010, 04:00 AM
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#9
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Senior Member
Registered: Sep 2004
Distribution: FreeBSD 9.1, Kubuntu 12.10
Posts: 2,967
Rep:
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Quote:
Originally Posted by wje_lq
Not to prove the point, but to provide more information. I'd like to read about this random inode number assignment idea in more detail. Why would they do this? (for example)
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Security? One might derive some useful information from a file system based on the ordering of the inodes. I totally made that up, but it seems like something the government would do.
Kevin Barry |
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01-01-2010, 06:36 AM
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#10
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Senior Member
Registered: Oct 2005
Distribution: Gentoo, Slackware, LFS
Posts: 2,052
Rep:
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maybe for quicker inode searching algorithms?
Code:
for (n = x; n; ++n) {
...
n = n->next; # something similar?
}
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01-07-2010, 06:33 AM
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#11
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Senior Member
Registered: Jan 2005
Location: Melbourne, Australia
Distribution: Debian Squeeze (Fluxbox WM)
Posts: 1,357
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Quote:
Originally Posted by sundialsvcs
Many Linux and Unix systems actually use inode numbers now that are random.
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That might be true of a particular filesystem. But on Linux filesystems at least, many of the inode numbering schemes are simply an incrementing counter (exceptions including things like the implementation of FAT). The inode number does get hashed for lookup purposes.
Last edited by neonsignal; 01-07-2010 at 06:34 AM.
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1 members found this post helpful.
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