[PATCH] makedevs: make special node creation idempotent

[Arnout Vandecappelle (Essensium/Mind)]

When makedevs is called for a second time with the same device file, it
will fail because the files already exist and mknod() gives -EEXISTS.

To avoid this, check if the file already exists and if so, if it is of
the right type. The chmod and chown changes are still done.

function                                             old     new   delta
makedevs_main                                       1086    1201    +115
.rodata                                           138731  138832    +101
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 216/0)             Total: 216 bytes
   text    data     bss     dec     hex filename
 856021   15958    1968  873947   d55db busybox_old
 856237   15958    1968  874163   d56b3 busybox_unstripped

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
---
 miscutils/makedevs.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/miscutils/makedevs.c b/miscutils/makedevs.c
index c945a13..49f011d 100644
--- a/miscutils/makedevs.c
+++ b/miscutils/makedevs.c
@@ -225,6 +225,7 @@ int makedevs_main(int argc UNUSED_PARAM, char **argv)
 			dev_t rdev;
 			unsigned i;
 			char *full_name_inc;
+			struct stat st;
 
 			if (type == 'p') {
 				mode |= S_IFIFO;
@@ -244,10 +245,23 @@ int makedevs_main(int argc UNUSED_PARAM, char **argv)
 			for (i = start; i <= start + count; i++) {
 				sprintf(full_name_inc, count ? "%s%u" : "%s", full_name, i);
 				rdev = makedev(major, minor + (i - start) * increment);
-				if (mknod(full_name_inc, mode, rdev) < 0) {
+				if (stat(full_name_inc, &st) == 0) {
+					if ((mode & S_IFMT) != (st.st_mode & S_IFMT)) {
+						bb_error_msg("line %d: node %s exists but is of wrong file type", linenum, full_name_inc);
+						ret = EXIT_FAILURE;
+						continue;
+					}
+					if (st.st_rdev != rdev) {
+						bb_error_msg("line %d: node %s exists but is wrong device number", linenum, full_name_inc);
+						ret = EXIT_FAILURE;
+						continue;
+					}
+				} else if (mknod(full_name_inc, mode, rdev) < 0) {
 					bb_perror_msg("line %d: can't create node %s", linenum, full_name_inc);
 					ret = EXIT_FAILURE;
-				} else if (chown(full_name_inc, uid, gid) < 0) {
+					continue;
+				}
+				if (chown(full_name_inc, uid, gid) < 0) {
 					bb_perror_msg("line %d: can't chown %s", linenum, full_name_inc);
 					ret = EXIT_FAILURE;
 				} else if (chmod(full_name_inc, mode) < 0) {
-- 
2.9.3