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udev: serialize/synchronize block device event handling with file locks

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This commit is contained in:
Kay Sievers 2014-04-13 19:54:27 -07:00
parent 2f1a3d0868
commit 3ebdb81ef0
1 changed files with 31 additions and 2 deletions
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33
src/udev/udevd.c
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@ -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);