Messages in this thread | | | Date | Fri, 2 Apr 2004 23:39:34 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH] cowlinks v2 |
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Hi!
> > Okay, now I have to start talking about implementation. Assume ext2 as > > a base. Theres new object "cowid" which contains, well, id for > > get_data_id() and usage count. Each inode either has pointer to > > "cowid" object, or it is plain old regular file. > > Pavel has it exactly right. > > A simple way to store COWID objects in the filesystem itself is as > another ordinary inode. The attributes of that inode (mtime, mode > etc.) aren't important (except to fsck), only the size and data > pointers are important. The files which point to a COWID need a flag > to indicate that, too.
Actually, my solution has one weirdness...
> a copyfile a b rm a
...now b has pointer to cowid with usage count of 1. Which is slightly ugly (and wastes one cowid entry), but should be harmless.
> get_data_id() is one way to detect equivalent files. Another would be > a function files_equal(fd1, fd2) which returns a boolean.
files_equal(...) would lead to quadratic number of calls, no?
> get_data_id() has the advantage that it can report immediately whether > a file has _any_ cowlink peers, which is important for programs that > scan trees. Perhaps getxattr() would be reasonable interface, using a > named attribute "data-id".
Yes, get_data_id() is extremely ugly name. Pavel -- When do you have a heart between your knees? [Johanka's followup: and *two* hearts?] - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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