hard links to files on other filesystems disallowed: why?
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From: The Natural Philosopher on 20 Feb 2010 15:09 Rahul 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 is a structural reason. Hard links are duplicate directory entries actually on the disk. They cannot refer to another disk.
From: The Natural Philosopher on 20 Feb 2010 15:14 J G Miller 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? ;) she may be superposed in an infinitee number of places if her name is Schrödinger..
From: Rahul on 20 Feb 2010 17:04 The Natural Philosopher <tnp(a)invalid.invalid> wrote in news:hlpfid$b1j$3 @news.albasani.net: > There is a structural reason. > > Hard links are duplicate directory entries actually on the disk. > > They cannot refer to another disk. > Thanks for the explanations guys. I think I understand how it is done. Buy nothing in these explainations precludes why the links cannot point to a inode on another filesystem that is also mounted. If two filessytems are both mounted all storage on them is pretty much identical in terms of inodes etc. , right? Or maybe I don't see the obvious.... -- Rahul
From: Jerry Peters on 20 Feb 2010 17:15 Rahul <nospam(a)invalid.invalid> wrote: > The Natural Philosopher <tnp(a)invalid.invalid> wrote in news:hlpfid$b1j$3 > @news.albasani.net: > >> There is a structural reason. >> >> Hard links are duplicate directory entries actually on the disk. >> >> They cannot refer to another disk. >> > > Thanks for the explanations guys. I think I understand how it is done. Buy > nothing in these explainations precludes why the links cannot point to a > inode on another filesystem that is also mounted. If two filessytems are > both mounted all storage on them is pretty much identical in terms of > inodes etc. , right? Or maybe I don't see the obvious.... > The directory entry contains the inode number in this filesystem. Let's suppose it also contained some sort of FS info. What would that be? It can't be a device number because there's no guarantee that the device number is a constant (USB devices in particular). So how do you "point" to the other FS? Jerry
From: Dan Mills on 20 Feb 2010 17:17
On Sat, 20 Feb 2010 22:04:47 +0000, Rahul wrote: > Thanks for the explanations guys. I think I understand how it is done. > Buy nothing in these explainations precludes why the links cannot point > to a inode on another filesystem that is also mounted. How do you tell which file systems inode the number refers to? Inodes are not unique system wide, only within a single filesystem. > If two > filessytems are both mounted all storage on them is pretty much > identical in terms of inodes etc. , right? Or maybe I don't see the > obvious.... An Inode number is ONLY unique within a file system, so a directory entry can only point to an inode within the same file system. Inode 12345 is only sufficient to identify a file within a file system, it is not sufficient to identify a file system wide as there may be many mounted file systems and quite a few of them could have an inode numbered 12345. Regards, Dan. |