mdev: support for serializing hotplug

function                                             old     new   delta
mdev_main                                            503     647    +144

1 files changed, 28 insertions, 3 deletions

diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index c61521cbb..8968e45f8 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -374,8 +374,6 @@ static void load_firmware(const char *const firmware, const char *const sysfs_pa
 int mdev_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int mdev_main(int argc UNUSED_PARAM, char **argv)
 {
-        char *action;
-        char *env_path;
         RESERVE_CONFIG_BUFFER(temp, PATH_MAX + SCRATCH_SIZE);
 
         /* We can be called as hotplug helper */
@@ -417,8 +415,14 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
                         ACTION_RECURSE | ACTION_FOLLOWLINKS,
                         fileAction, dirAction, temp, 0);
         } else {
+                char *seq;
+                char *action;
+                char *env_path;
+                char seqbuf[sizeof(int)*3 + 2];
+                int seqlen = seqlen; /* for compiler */
+
                 /* Hotplug:
-                 * env ACTION=... DEVPATH=... mdev
+                 * env ACTION=... DEVPATH=... [SEQNUM=...] mdev
                  * ACTION can be "add" or "remove"
                  * DEVPATH is like "/block/sda" or "/class/input/mice"
                  */
@@ -427,6 +431,23 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
                 if (!action || !env_path)
                         bb_show_usage();
 
+                seq = getenv("SEQNUM");
+                if (seq) {
+                        int timeout = 2000 / 32;
+                        do {
+                                seqlen = open_read_close("mdev.seq", seqbuf, sizeof(seqbuf-1));
+                                if (seqlen < 0)
+                                        break;
+                                seqbuf[seqlen] = '\0';
+                                if (seqbuf[0] == '\n' /* seed file? */
+                                 || strcmp(seq, seqbuf) == 0 /* correct idx? */
+                                ) {
+                                        break;
+                                }
+                                usleep(32*1000);
+                        } while (--timeout);
+                }
+
                 snprintf(temp, PATH_MAX, "/sys%s", env_path);
                 if (!strcmp(action, "remove"))
                         make_device(temp, 1);
@@ -439,6 +460,10 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
                                         load_firmware(fw, temp);
                         }
                 }
+
+                if (seq && seqlen >= 0) {
+                        xopen_xwrite_close("mdev.seq", utoa(xatou(seq) + 1));
+                }
         }
 
         if (ENABLE_FEATURE_CLEAN_UP)