Messages in this thread | | | Date | Sat, 12 Jun 1999 10:43:27 +0200 | From | Thomas Pornin <> | Subject | mount union |
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Hello,
I don't think this issue has been recently discussed, but if what I ask is stupid, please do not shoot me.
BSD has an option called 'union' that makes it somehow merge a mounted filesystem with the files that already exist: files are created on the newly mounted filesystem, but the underlying files may be accessed if no file with the same name exists on the new filesystem.
I really like this because it is really fun, and, moreover, it might as well be useful, for instance for: -- diskless machines: /etc NFS mounted, same for every one, with a very small ramdisk mounted over it, that contains the machine-specific information -- compiling from a cdrom with sources (writes are done on a disk), or from a read-only partition -- sharing /usr/local across different architectures, with only binaries that differ (data files, shell scripts, perl scripts are identical, therefore not copied)(sounds like Plan9)
Is this handled by some patch somewhere ? Or are some people working on it ? Is it feasible easily at least ?
Another related fun feature: one filesystem read-only, another one mounted read/write over it. When you open a file for writing, if it is on the read-only filesystem, it is first copied on the read/write one. It would be some sort of patching filesystem.
Ok, maybe all of this is just lunatic ranting.
--Thomas Pornin
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