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-rw-r--r--src/udev/udevd.c33
1 files changed, 31 insertions, 2 deletions
diff --git a/src/udev/udevd.c b/src/udev/udevd.c
index f9ee36870b..aecd208d40 100644
--- a/src/udev/udevd.c
+++ b/src/udev/udevd.c
@@ -31,6 +31,7 @@
#include <time.h>
#include <getopt.h>
#include <dirent.h>
+#include <sys/file.h>
#include <sys/time.h>
#include <sys/prctl.h>
#include <sys/socket.h>
@@ -265,6 +266,7 @@ static void worker_new(struct event *event)
for (;;) {
struct udev_event *udev_event;
struct worker_message msg;
+ int fd_lock = -1;
int err;
log_debug("seq %llu running", udev_device_get_seqnum(dev));
@@ -280,6 +282,30 @@ static void worker_new(struct event *event)
if (exec_delay > 0)
udev_event->exec_delay = exec_delay;
+ /*
+ * Take a "read lock" on the device node; this establishes
+ * a concept of device "ownership" to serialize device
+ * access. External processes holding a "write lock" will
+ * cause udev to skip the event handling; in the case udev
+ * acquired the lock, the external process will block until
+ * udev has finished its event handling.
+ */
+ if (streq_ptr("block", udev_device_get_subsystem(dev))) {
+ struct udev_device *d = dev;
+
+ if (streq_ptr("partition", udev_device_get_devtype(d)))
+ d = udev_device_get_parent(d);
+
+ if (d) {
+ fd_lock = open(udev_device_get_devnode(d), O_RDONLY|O_CLOEXEC|O_NOFOLLOW|O_NONBLOCK);
+ if (fd_lock >= 0 && flock(fd_lock, LOCK_SH|LOCK_NB) < 0) {
+ log_debug("Unable to flock(%s), skipping event handling: %m", udev_device_get_devnode(d));
+ err = -EWOULDBLOCK;
+ goto skip;
+ }
+ }
+ }
+
/* apply rules, create node, symlinks */
err = udev_event_execute_rules(udev_event, rules, &sigmask_orig);
@@ -292,13 +318,16 @@ static void worker_new(struct event *event)
udev_device_update_db(dev);
}
+ if (fd_lock >= 0)
+ close(fd_lock);
+
/* send processed event back to libudev listeners */
udev_monitor_send_device(worker_monitor, NULL, dev);
+skip:
/* send udevd the result of the event execution */
memzero(&msg, sizeof(struct worker_message));
- if (err != 0)
- msg.exitcode = err;
+ msg.exitcode = err;
msg.pid = getpid();
send(worker_watch[WRITE_END], &msg, sizeof(struct worker_message), 0);