On Tue, Apr 28, 2015 at 04:46:46PM +0200, Beata Michalska wrote: > On 04/28/2015 04:09 PM, Greg KH wrote: > > On Tue, Apr 28, 2015 at 03:56:53PM +0200, Jan Kara wrote: > >> On Mon 27-04-15 17:37:11, Greg KH wrote: > >>> On Mon, Apr 27, 2015 at 05:08:27PM +0200, Beata Michalska wrote: > >>>> On 04/27/2015 04:24 PM, Greg KH wrote: > >>>>> On Mon, Apr 27, 2015 at 01:51:41PM +0200, 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 newly introduced multicast group. > >>>>>> > >>>>>> Threshold notifications have been included, allowing > >>>>>> 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> > >>>>>> --- > >>>>>> Documentation/filesystems/events.txt | 231 ++++++++++ > >>>>>> fs/Makefile | 1 + > >>>>>> fs/events/Makefile | 6 + > >>>>>> fs/events/fs_event.c | 770 ++++++++++++++++++++++++++++++++++ > >>>>>> fs/events/fs_event.h | 25 ++ > >>>>>> fs/events/fs_event_netlink.c | 99 +++++ > >>>>>> fs/namespace.c | 1 + > >>>>>> include/linux/fs.h | 6 +- > >>>>>> include/linux/fs_event.h | 58 +++ > >>>>>> include/uapi/linux/fs_event.h | 54 +++ > >>>>>> include/uapi/linux/genetlink.h | 1 + > >>>>>> net/netlink/genetlink.c | 7 +- > >>>>>> 12 files changed, 1257 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 > >>>>> > >>>>> Any reason why you just don't do uevents for the block devices today, > >>>>> and not create a new type of netlink message and userspace tool required > >>>>> to read these? > >>>> > >>>> The idea here is to have support for filesystems with no backing device as well. > >>>> Parsing the message with libnl is really simple and requires few lines of code > >>>> (sample application has been presented in the initial version of this RFC) > >>> > >>> I'm not saying it's not "simple" to parse, just that now you are doing > >>> something that requires a different tool. If you have a block device, > >>> you should be able to emit uevents for it, you don't need a backing > >>> device, we handle virtual filesystems in /sys/block/ just fine :) > >>> > >>> People already have tools that listen to libudev for system monitoring > >>> and management, why require them to hook up to yet-another-library? And > >>> what is going to provide the ability for multiple userspace tools to > >>> listen to these netlink messages in case you have more than one program > >>> that wants to watch for these things (i.e. multiple desktop filesystem > >>> monitoring tools, system-health checkers, etc.)? > >> As much as I understand your concerns I'm not convinced uevent interface > >> is a good fit. There are filesystems that don't have underlying block > >> device - think of e.g. tmpfs or filesystems working directly on top of > >> flash devices. These still want to send notification to userspace (one of > >> primary motivation for this interfaces was so that tmpfs can notify about > >> something). And creating some fake nodes in /sys/block for tmpfs and > >> similar filesystems seems like doing more harm than good to me... > > > > If these are "fake" block devices, what's going to be present in the > > block major/minor fields of the netlink message? For some reason I > > thought it was a required field, and because of that, I thought we had a > > "real" filesystem somewhere to refer to, otherwise how would userspace > > know what filesystem was creating these events? > > > > What am I missing here? > > > > confused, > > > > greg k-h > > > > For those 'fake' block devs, upon mount, get_anon_bdev will assign > the major:minor numbers. Userspace might get those through stat. How can userspace do the mapping backwards from this "anonymous" major:minor number for these types of filesystems in such a way that they can "know" how to report the block device that is causing the event? thanks, greg k-h -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>