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Date: Fri, 11 Jul 2008 22:05:40 +0200
From: Christian Franke <Christian DOT Franke AT t-online DOT de>
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Subject: CoPy to /dev/null fails
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Hi,

this works on Linux:

$ cp file /dev/null

but fails on Cygwin 1.5.25-15:

$ cp file /dev/null
cp: cannot create regular file `/dev/null': Invalid request code


/dev/null exists, so /bin/cp opens it with O_TRUNC only. But this fails 
with EBADRQC (54):

  fd = open("/dev/null", O_WRONLY|O_TRUNC, .)

According to strace, Cygwin calls:

  h = CreateFile("NUL", ., ., TRUNCATE_EXISTING, ., .);

which fails.


Interestingly, this works:

   fd = open("/dev/null", O_WRONLY|O_CREAT|O_TRUNC, .);

Cygwin calls:

  h = CreateFile("NUL", ., ., CREATE_ALWAYS, ., .);

Apparently a subtle (and IMO undocumented) difference between 
TRUNCATE_EXISTING and CREATE_ALWAYS even when file exists.

Christian


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