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Re: dd new iflag= oflag= flags directory, nolinks

From: Paul Eggert
Subject: Re: dd new iflag= oflag= flags directory, nolinks
Date: Tue, 07 Mar 2006 08:14:05 -0000
User-agent: Gnus/5.1007 (Gnus v5.10.7) Emacs/21.4 (gnu/linux)

Phillip Susi <address@hidden> writes:

> You can't open() and write() to a directory, so how does it make
> any sense to ask dd to set O_DIRECTORY?

You can open a directory without writing to it.  Something like this:

   $ mkdir foo
   $ dd if=foo iflag=directory count=0
   0+0 records in
   0+0 records out
   0 bytes (0 B) copied, 2e-05 seconds, 0 B/s

You can think of this as a way to do a "test -d foo && test -r foo"
atomically, without race conditions.  Admittedly this is somewhat
twisted, but the new documentation does say that iflag=directory is of
"limited utility"....

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