backup linked files

[Christos Ricudis]

In article <mailman.1016804466.11555.linux-greek-users at lists.hellug.gr>, Alex Papadopoulos wrote:

> [1] To problhma einai oti den mporw na kanw hard link se directory. To 
> man page tou ln leei oti o root mporei na to kanei, alla dokimasa kai h 
> apanthsh htan:
> 
> root at helios:/home/alex > ln -d docs/HOWTO/ HOWTO
> ln: creating hard link `HOWTO' to `docs/HOWTO/': Operation not permitted
> 
> ..to idio kai xwris to -d, to idio kai me -F. Pws ginetai pleon ayto?

Den ginetai, kai yparxei poly kalos logos poy den ginetai. An epitrepotan 
ta hard links se directory, to filesystem 8a mporouse na metatrapei apo dentro
se kykliko grafo: 

Estw : 

a/
a/b/
a/b/c/

kai mesa sto c/ kanoume ena hard link d poy deixnei pisw sto a/. Ti kaname? 
Kaname mia domh h opoia : 

1) ginetai traverse ep'apeiron (a/b/c/d/b/c/d/b/c/d/ ktl ktl)

kai 

2) den mporei na sbhstei (exoume ena kyklo apo tria directories poy kanena 
toys den mporei na apokthsei mhdeniko reference count wste na epitrapei h 
diagrafh toy).

H lysh sou bebaia einai na kaneis duplicate to directory structure poy 8eleis 
katw apo to backup subdir, kai na kaneis hard links mono sta actual files. 

> [2] H anhsyxia einai h ekshs: (apo to man page tou mkisofs)
> 
> BUGS
>        o      Any  files that have hard links to files not in the
>               tree being copied to the  iso9660  filesystem  will
>               have an incorrect file reference count.

Mh se anhsyxei. To file reference count se ena read-only meso den exei 
apolytws kammia xrhsimothta. Se read-write mediums, eksyphretei o,ti 
kai ola ta object reference counts - oso to reference count den einai 
mhdeniko, to object de ginetai deallocate : 

Exoume ena arxeio kai dyo hard links poy deixnoun sto arxeio (praktika dhladh
exoume treia arxeia poy deixnoyn sto idio i-node, mia poy den yparxei 
apolytws kammia diafora metaksy enos arxeiou kai enos hard link toy) : 

manitari:[ricudis]~/test$ echo > kota ; ln kota rapanaki ; ln rapanaki pepperoni ; ls -l 
total 3
-rw-r--r--   3 ricudis  users           1 Mar 23 00:35 kota
-rw-r--r--   3 ricudis  users           1 Mar 23 00:35 pepperoni
-rw-r--r--   3 ricudis  users           1 Mar 23 00:35 rapanaki

Parathroume oti kai ta 3 arxeia exoun file reference count 3. Trwme to 
pepperoni : 

manitari:[ricudis]~/test$ rm pepperoni ; ls -l 
total 2
-rw-r--r--   2 ricudis  users           1 Mar 23 00:35 kota
-rw-r--r--   2 ricudis  users           1 Mar 23 00:35 rapanaki
manitari:[ricudis]~/test$

To file reference count toy i-node meiw8hke sto 2, alla to arxeio paramenei 
profanws sth 8esh toy, den diagrafetai oso yparxoyn arxeia poy deixnoyn 
sto sygkekrimeno i-node. 

Trwme kai to rapanaki, meiwnontas to reference count sto 1 : 

manitari:[ricudis]~/test$ rm rapanaki ; ls -l
total 1
-rw-r--r--   1 ricudis  users           1 Mar 23 00:35 kota
manitari:[ricudis]~/test$

To reference count exei meiw8ei sto 1. To epomeno rm sthn kota, 8a sbhsei to
arxeio kai mia poy to reference count toy i-node 8a mhdenistei, 8a diagrafei
KAI to i-node. 

Ennoeitai oti ola ayta einai ligaki unapplicable se read-only filesystems
opws to ISO9660. De 8a to xarakthriza akribws 'bug'. 




-- 
Christos Ricudis

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