On Fri 17-04-15 16:44:16, Andreas Dilger wrote: > On Apr 17, 2015, at 5:31 AM, Jan Kara <jack@xxxxxxx> wrote: > > On Wed 15-04-15 09:15:44, Beata Michalska wrote: > >> Introduce configurable generic interface for file > >> system-wide event notifications to provide file > >> systems with a common way of reporting any potential > >> issues as they emerge. > >> > >> The notifications are to be issued through generic > >> netlink interface, by a dedicated, for file system > >> events, multicast group. The file systems might as > >> well use this group to send their own custom messages. > >> > >> The events have been split into four base categories: > >> information, warnings, errors and threshold notifications, > >> with some very basic event types like running out of space > >> or file system being remounted as read-only. > >> > >> Threshold notifications have been included to allow > >> triggering an event whenever the amount of free space > >> drops below a certain level - or levels to be more precise > >> as two of them are being supported: the lower and the upper > >> range. The notifications work both ways: once the threshold > >> level has been reached, an event shall be generated whenever > >> the number of available blocks goes up again re-activating > >> the threshold. > >> > >> The interface has been exposed through a vfs. Once mounted, > >> it serves as an entry point for the set-up where one can > >> register for particular file system events. > >> > >> Signed-off-by: Beata Michalska <b.michalska@xxxxxxxxxxx> > > Thanks for the patches! Some comments are below. > > > >> --- > >> Documentation/filesystems/events.txt | 254 +++++++++++ > >> fs/Makefile | 1 + > >> fs/events/Makefile | 6 + > >> fs/events/fs_event.c | 775 ++++++++++++++++++++++++++++++++++ > >> fs/events/fs_event.h | 27 ++ > >> fs/events/fs_event_netlink.c | 94 +++++ > >> fs/namespace.c | 1 + > >> include/linux/fs.h | 6 +- > >> include/linux/fs_event.h | 69 +++ > >> include/uapi/linux/fs_event.h | 62 +++ > >> include/uapi/linux/genetlink.h | 1 + > >> net/netlink/genetlink.c | 7 +- > >> 12 files changed, 1301 insertions(+), 2 deletions(-) > >> create mode 100644 Documentation/filesystems/events.txt > >> create mode 100644 fs/events/Makefile > >> create mode 100644 fs/events/fs_event.c > >> create mode 100644 fs/events/fs_event.h > >> create mode 100644 fs/events/fs_event_netlink.c > >> create mode 100644 include/linux/fs_event.h > >> create mode 100644 include/uapi/linux/fs_event.h > >> > >> diff --git a/Documentation/filesystems/events.txt b/Documentation/filesystems/events.txt > >> new file mode 100644 > >> index 0000000..c85dd88 > >> --- /dev/null > >> +++ b/Documentation/filesystems/events.txt > >> @@ -0,0 +1,254 @@ > >> + > >> + Generic file system event notification interface > >> + > >> +Document created 09 April 2015 by Beata Michalska <b.michalska@xxxxxxxxxxx> > >> + > >> +1. The reason behind: > >> +===================== > >> + > >> +There are many corner cases when things might get messy with the filesystems. > >> +And it is not always obvious what and when went wrong. Sometimes you might > >> +get some subtle hints that there is something going on - but by the time > >> +you realise it, it might be too late as you are already out-of-space > >> +or the filesystem has been remounted as read-only (i.e.). The generic > >> +interface for the filesystem events fills the gap by providing a rather > >> +easy way of real-time notifications triggered whenever something intreseting > >> +happens, allowing filesystems to report events in a common way, as they occur. > >> + > >> +2. How does it work: > >> +==================== > >> + > >> +The interface itself has been exposed as fstrace-type Virtual File System, > >> +primarily to ease the process of setting up the configuration for the file > >> +system notifications. So for starters it needs to get mounted (obviously): > >> + > >> + mount -t fstrace none /sys/fs/events > >> + > >> +This will unveil the single fstrace filesystem entry - the 'config' file, > >> +through which the notification are being set-up. > >> + > >> +Activating notifications for particular filesystem is as straightforward > >> +as writing into the 'config' file. Note that by default all events despite > >> +the actual filesystem type are being disregarded. > > Is there a reason to have a special filesystem for this? Do you expect > > extending it by (many) more files? Why not just creating a file in sysfs or > > something like that? > > > >> +Synopsis of config: > >> +------------------ > >> + > >> + MOUNT EVENT_TYPE [L1] [L2] > >> + > >> + MOUNT : the filesystem's mount point > > I'm not quite decided but is mountpoint really the right thing to pass > > via the interface? They aren't unique (filesystem can be mounted in > > multiple places) and more importantly can change over time. So won't it be > > better to pass major:minor over the interface? These are stable, unique to > > the filesystem, and userspace can easily get them by calling stat(2) on the > > desired path (or directly from /proc/self/mountinfo). That could be also > > used as an fs identifier instead of assigned ID (and thus we won't need > > those events about creation of new trace which look somewhat strange to > > me). > > > > OTOH using major:minor may have issues in container world where processes > > could watch events from filesystems inaccessible to the container if they > > guess the device number. So maybe we could use 'path' when creating new > > trace but I'd still like to use the device number internally and for all > > outgoing communication because of above mentioned problems with > > mountpoints. > > Please don't make major:minor part of the interface. That doesn't make > sense for network filesystems. Using the mountpoint to set this up is > fine, and really what is expected by userspace tools to monitor a specific > mountpoint. We could use sb->s_id to identify the events. So for setup I agree that mountpoint is probably the easiest. For reporting back from kernel, sb->s_id isn't enough because as Beata noted, this isn't unique. You are right that for network filesystems (or in-memory filesystem for that matter) device number doesn't make any particular sense but each fs (even e.g. procfs) is assigned a "virtual" device number which uniquely identifies that filesystem. You can see that device number in /proc/self/mountinfo and you will also see it in st_dev from stat(2). So using that is IMHO better than devising own unique number. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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