hard links to files on other filesystems disallowed: why?
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From: Grant Edwards on 20 Feb 2010 23:47 On 2010-02-21, Rahul <nospam(a)nospam.invalid> wrote: > Grant Edwards <invalid(a)invalid.invalid> wrote in news:hlpf6m$s6j$1 > @reader2.panix.com: > >> If you launch her through a double-slit setup, isn't it >> possible for her to pass through _both_ her house and your >> house? > > Are "entangled nieces" a possibility? Definitely. My neice in Australia seemed to know it when my neice in the US went into labor two weeks ago. If that's not entanglement, I don't know what is... -- Grant
From: Marc Haber on 21 Feb 2010 04:29 Rahul <nospam(a)invalid.invalid> 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. (1) echo "foo" > foo.1 (2) ln foo.1 foo.2 (3) echo "bar" > foo.2 (4) cat foo.1 Try this on a normal system, and then try this on a system with your suggested new hard link semantics. Optionally, repeat this test after umounting (and optionally physically removing the device holding) the file system where foo1 is stored on as step (2a). Greetings Marc -- -------------------------------------- !! No courtesy copies, please !! ----- Marc Haber | " Questions are the | Mailadresse im Header Mannheim, Germany | Beginning of Wisdom " | http://www.zugschlus.de/ Nordisch by Nature | Lt. Worf, TNG "Rightful Heir" | Fon: *49 621 72739834
From: Marten Kemp on 21 Feb 2010 08:27 Rahul wrote: > Dan Mills <dmills(a)exponent.myzen.co.uk> wrote in > news:4b805f72$0$2533$da0feed9(a)news.zen.co.uk: > >> How do you tell which file systems inode the number refers to? Inodes >> are not unique system wide, only within a single filesystem. > > True. But that's just how the current implimentation is. One could always > use a [ uuid, inode] tuple where the uuid uniquely referred to the foreign > file system. > > Again, I'm not saying "this ougt to be done" or "this is easy to do" etc. > BUt just trying to figure out how come this "feature" never crept in? Are > there other compelling reasons besides a lack of implimentation not to > allow cross file system hard links? I see several reasons why people might > want cross-FS-hardlinks. > > Another way to put this: Hypothetically, if some smart guy were to try and > write his OS would this be an OK feature? Use a 'volser' (volume serial number) to identify partitions as is done in some mainframe OSen. I come from a zVM background and the actual device address isn't part of a partition's location. The mapping of the volser to the device address is done by the OS at the time the device is mounted, giving you the ability to move file systems between devices without a large amount of pain. I'd much rather deal with 'doofus-root' than with 'hda1' in fstab, for example. Cross-FS-hardlinks could be special entries containing the volser where the FS is to be found and the inode within the FS. I'd be willing to wager that cross-FS-hardlinks weren't implemented because that would create a special type of pointer. -- -- Marten Kemp (Fix ISP to reply) You can't help being ignorant 'cause there's always something you don't know; what you can't be is stupid.
From: pk on 21 Feb 2010 08:42 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. It all boils down to where the data blocks are. True hardlinks (ie, on the same filesystem) share the inode, and thus the associated data blocks. If cross-fs hardlinks existed, then you'd have to find a way to share the data blocks between those two filesystems. If instead you keep the data on only one of the filesystems, then one of th links (that on the fs with no data blocks) would be no different from a symlink.
From: J G Miller on 21 Feb 2010 09:12
On Sat, 20 Feb 2010 22:15:25 -0500, despen wrote: > There is no requirement that the target of a soft link exist. Indeed not, but it does raise the issue of whether or not dangling links are dangerous and a potential security hole. |