On Wed 29-04-15 09:03:08, Beata Michalska wrote: > On 04/28/2015 07:39 PM, Greg KH wrote: > > 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 > > > > It needs to be done internally by the app but is doable. > The app knows what it is watching, so it can maintain the mappings. > So prior to activating the notifications it can call 'stat' on the mount point. > Stat struct gives the 'st_dev' which is the device id. Same will be reported > within the message payload (through major:minor numbers). So having this, > the app is able to get any other information it needs. > Note that the events refer to the file system as a whole and they may not > necessarily have anything to do with the actual block device. Or you can use /proc/self/mountinfo for the mapping. There you can see device numbers, real device names if applicable and mountpoints. This has the advantage that it works even if filesystem mountpoints change. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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>