MFS root filesystem and static binaries size

[Stanislav Zaharov]

On Wed, Oct 17, 2012 at 12:13 AM, Devin Teske <devin.teske at fisglobal.com>wrote:

>
> On Oct 16, 2012, at 11:13 AM, Stanislav Zaharov wrote:
>
> Hello,
>
> I have a question regarding the mfsroot file system organization on
> installation cd.
> How is it possible that we have bigger binary files in ls list while actual
> occupied space is less.
>
>
> The beauty of crunchgen(1).
>
> If you use the "-i" flag to ls, you'll see the inode numbers (and
> subsequently notice that a great-many inodes are identical).
>
> When two files have the same inode, they are "hard links" to each other.
> Unlike a "soft link" (or "symbolic link" as they are more appropriately
> called), which stores a destination-path of the target, a hard link instead
> looks and acts no different than the original in every way.
>
> So, I can hear you asking, if all these binaries are linked to the same
> file, what file is that?
>
> /stand/boot_crunch
>
> This is a "crunched" binary (produced by crunchgen(1)).
>
> Here's the configuration file that is fed to crunchgen(1) that produces
> this binary:
>
> http://svn.freebsd.org/base/stable/9/release/i386/boot_crunch.conf
>
> Quite simply, crunchgen(1) takes a list of programs (progs) and libraries
> (libs) and produces a "crunched" binary.
>
> You then create links (hard or soft) to the crunched binary. The crunched
> binary knows by argv[0] which main() subroutine to invoke.
>
> This ultimately allows things to stay nice and tight (storage space-wise).
>
>
>
> But when we try to copy these files on similar
> filesystem using cp or dd the actual used space is bigger?
>
>
> cp(1) doesn't track hard-links.
>
> tar(1) does.
>
> If you want to copy /stand out of the mfsroot, you can do this:
>
> mkdir /stand2
> tar cf - /stand | tar xf - -C /stand2
>
> A corresponding "ls -li /stand2" should show that the majority of files
> all have the same inode (whereas if you use cp, "ls -li" will instead show
> different inodes for every file that was copied, because again, cp(1) does
> not support retention of hard-links).
>
>
>
>
> For example when we mount mfsroot image we get:
>
> $ df -h /mnt/
>
> Filesystem    Size    Used   Avail Capacity  Mounted on
> /dev/md0      3.9M    3.3M    534k    86%    /mnt
>
> $ ls -lhs /mnt/stand
> ...
>  766 -r-xr-xr-x  30 root  wheel     3M 10 apr  2012 dhclient
>  766 -r-xr-xr-x  30 root  wheel     3M 10 apr  2012 cpio
>  766 -r-xr-xr-x  30 root  wheel     3M 10 apr  2012 camcontrol
>  766 -r-xr-xr-x  30 root  wheel     3M 10 apr  2012 boot_crunch
> ...
>
> But:
>
> $ du -hc /mnt/stand
> ...
> 3,2M    total
>
>
> But if we copy these files onto another UFS filesystem we really consume
> the space:
>
> $ cp -a /mnt/stand /tmp/stand
>
> $ du -hc /tmp/stand
> ...
> 91M    total
>
>
> How is it possible and why does it matter for mfsroot?
>
>
> The reason crunchgen(1) is used to create /stand/boot_crunch for the
> install media (mfsroot) is to save space and simplify the environment. When
> using a crunched binary, there are no libraries to worry about for example
> (all the libraries are compiled-in).
> --
> Cheers,
> Devin
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>


Thank you for the explanation!
-- 
Respectfully,
Stanislav Putrya
System & network administrator
WWW: fotostrana.ru
WWW2: bsdway.ru
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e-mail: root.vagner at gmail.com
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