[PATCH 3/3] kvmtool/run: do not overwrite /virt/init

[Oleg Nesterov <oleg@redhat.com>]

To me kvm_setup_guest_init() behaviour looks "obviously wrong" and
unfriendly because it always overwrites /virt/init.

kvm_setup_guest_init() is also called when we are going to use this
tree as a rootfs, and without another patch ("kvmtool/run: append
cfg.kernel_cmdline at the end of real_cmdline") the user can't use
"lkvm run -p init=my_init_path". This simply means that you can not
use a customized init unless you patch kvmtool.

Change extract_file() to do nothing if the file already exists. This
should not affect do_setup() which calls kvm_setup_guest_init() only
if make_dir(guestfs_name) creates the new/empty dir.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 builtin-setup.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/builtin-setup.c b/builtin-setup.c
index 1e5b1e4..8be8d62 100644
--- a/builtin-setup.c
+++ b/builtin-setup.c
@@ -130,10 +130,14 @@ static int extract_file(const char *guestfs_name, const char *filename,
 
 	snprintf(path, PATH_MAX, "%s%s/%s", kvm__get_dir(),
 				guestfs_name, filename);
-	remove(path);
-	fd = open(path, O_CREAT | O_WRONLY, 0755);
-	if (fd < 0)
+
+	fd = open(path, O_EXCL | O_CREAT | O_WRONLY, 0755);
+	if (fd < 0) {
+		if (errno == EEXIST)
+			return 0;
 		die("Fail to setup %s", path);
+	}
+
 	ret = xwrite(fd, data, (size_t)_size);
 	if (ret < 0)
 		die("Fail to setup %s", path);
-- 
2.4.3