open with O_EXCL and O_TRUNC

[Tom Brown]

on src/rcsedit.c:1426 of rcs version 5.7

#   define create(f) open(f, 
OPEN_O_BINARY|OPEN_O_LOCK|OPEN_O_WRONLY|O_CREAT|O_EXCL|O_TRUNC, 
OPEN_CREAT_READONLY) 

uses both the O_EXCL and O_TRUNC flags, which seem to describe mutally
exclusive behavior. The comments on lines 1382-1383 say this is atomic
according to Posix 1003.1-1990.

http://www.opengroup.org/onlinepubs/007904975/functions/open.html
does not say anything about the use of O_EXCL|O_TRUNC, except that any
combination of the flags are allowed.

What is the reason for O_EXCL|O_TRUNC instead of only O_EXCL? My only
guess would be truncating is used for locking on systems that don't
support O_EXCL, but I can't find the code to support that guess.

Tom


I bumped into this because the vfs driver (vmhgfs-only/driver.c) provided with 
VMWare build 5592 returns an error if O_CREAT|O_EXCL|O_TRUNC is set.

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