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c919f6f75c
In APIs such as guestfs_download, when the FileOut parameter exactly matches "/dev/stdout" or "/dev/stderr", don't reopen the possibly redirected output file with O_TRUNC (truncate). Instead dup the file descriptor. This magic behaviour doesn't happen for /dev/fd/* (or any other output file) allowing callers the choice of using /dev/stderr or /dev/fd/2 depending on whether or not they want truncation. This works around an annoying virt-builder bug. If you do: $ virt-builder fedora-21 --install no_such_package -v -x >& /tmp/log then when the `--install' command fails, virt-builder will download the log file using `guestfs_download (g, log, "/dev/stderr")'. Since this truncates the redirected /dev/stderr, the final log file is truncated and corrupted. With this patch the log file is no longer corrupted.