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From: Eric Blake <ebb9@byu.net>
Subject:  Re: Seems like treatment of NTFS ADS (foo:bar) changed between 1.5   and 1.7 but not mentioned in What's Changed
Date: Tue, 17 Nov 2009 17:36:48 +0000 (UTC)
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Thomas Wolff <towo <at> towo.net> writes:

> Sorry that I take this up once more (after promising <end:of>), but I 
> had this additional idea after seeing your point about being strictly 
> consistent with the POSIX pathname namespace:
> 
> So what about using "/" as a delimiter? If "foo" is a file, "foo/bar" is 
> not a legal pathname in POSIX, so it could be used to access the "bar" 
> fork of "foo" without causing real harm.

NO - a thousand times no.  Using / in file names, but not as a directory, is 
just ASKING to break everything ever written, and penalize speed of interfaces 
that could care less about this.

But, you _could_ borrow a leaf from Solaris, and support and implementation:

openat(open("foo",flags), "bar", flags)

as a way to open the "bar" stream of the "foo" fd, aka "foo:bar" in windows 
terms.  In other words, open("foo/bar") MUST fail, because foo is not a 
directory, but openat(fd_of_foo,"bar") is an extension allowed by POSIX (just 
because we currently fail with ENOTDIR in that situation doesn't mean we have 
to); and by using the *at interfaces, we could isolate the performance penalty 
to just the situations where the fd is not a directory fd.

You would also want to consider implementing opendir2 (borrowing from BSD 
heritage; there, opendir2 exists to allow the user to select whether whiteout 
entries in a union mount will be ignored), and adding a new DTF_* bit that 
allows opening a file to traverse its alternate streams, instead of the normal 
opening a directory to traverse its contents.

But I won't be writing the patches to do that.

-- 
Eric Blake




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