hard links to files on other filesystems disallowed: why?
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From: Rahul on 20 Feb 2010 13:14 Linux only allows hard-links to be made to files on the same filesystem. Is there a structural reason for this or just legacy of the "founding fathers"? Just curious. -- Rahul
From: Grant Edwards on 20 Feb 2010 13:29 On 2010-02-20, Rahul <nospam(a)invalid.invalid> wrote: > Linux only allows hard-links to be made to files on the same > filesystem. Is there a structural reason for this or just > legacy of the "founding fathers"? Just curious. There's a structural reason. A link is an association between a directory entry and an i-node number. I-node numbers are specific to filesystems. To allow links to files on other filesystems, the design of the directory entry would have to be changed to provide an association with a (filesystem,inode) tuple. AFIAK, there is no general, static way to refer to a specific filesystem the way there is for an inode to refer to a specific file within a filesystem. -- Grant
From: Robert Heller on 20 Feb 2010 14:06 At Sat, 20 Feb 2010 18:14:08 +0000 (UTC) Rahul <nospam(a)invalid.invalid> wrote: > > Linux only allows hard-links to be made to files on the same filesystem. Is > there a structural reason for this or just legacy of the "founding > fathers"? Just curious. It is structural. Kind of in the same way that while it is possible for me to have a *picture* of my niece in *my* house (eg a soft link), while she is at home in *her* house, it is not possible to have her *physically* present in my house, *while* she is also *physically* present in in her house. A hard link is just a directory entry pointing to a specific inode. Initially when a (normal) file is created, two things happen: an inode is allocated and a directory entry is created that points to this inode. It is then possible to create an additional directory entry that points to this same inode. This is all a 'hard-link' is. Nothing about the inode *itself* identifies the filesystem, beyond the fact that the when the inode was fetched, the I/O handle was associated with the file system. Oh, and there is no difference between the original link and the new link. Consider: touch foo ln foo bar rm foo The last two lines above are logicaly *identical* to: mv foo bar A soft link is something else. This is a small file whose contents is a path string. The file has a flag set to indicate that it is in fact a soft link. The path string can be anything and can reference anywhere in the logical file tree (same or different file system, local or remote, etc.). > -- Robert Heller -- 978-544-6933 Deepwoods Software -- Download the Model Railroad System http://www.deepsoft.com/ -- Binaries for Linux and MS-Windows heller(a)deepsoft.com -- http://www.deepsoft.com/ModelRailroadSystem/
From: J G Miller on 20 Feb 2010 14:15 On Sat, 20 Feb 2010 13:06:00 -0600, Robert Heller wrote: > it is not possible to have her *physically* present in my house, > *while* she is also *physically* present in in her house. If you know exactly how much momentum she has, can you be really sure where she is though? ;)
From: Grant Edwards on 20 Feb 2010 15:03
On 2010-02-20, J G Miller <miller(a)yoyo.ORG> wrote: > On Sat, 20 Feb 2010 13:06:00 -0600, Robert Heller wrote: > >> it is not possible to have her *physically* present in my house, >> *while* she is also *physically* present in in her house. > > If you know exactly how much momentum she has, can you be > really sure where she is though? ;) As long as we're going all quantum about it... If you launch her through a double-slit setup, isn't it possible for her to pass through _both_ her house and your house? -- Grant Edwards grante Yow! Isn't this my STOP?! at visi.com |