Hi, On 05/07/2015 01:57 PM, Beata Michalska wrote: > Hi, > > On 05/05/2015 02:16 PM, Beata Michalska wrote: >> Hi again, >> >> On 04/29/2015 11:13 AM, Greg KH wrote: >>> On Wed, Apr 29, 2015 at 09:42:59AM +0200, Jan Kara wrote: >>>> 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. >>> >>> How are you going to show an event for a filesystem that is made up of >>> multiple block devices? >>> >>>> 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. >>> >>> Ok, then that brings up my next question, how does this handle >>> namespaces? What namespace is the event being sent in? block devices >>> aren't namespaced, but the mount points are, is that going to cause >>> problems? >>> >>> thanks, >>> >>> greg k-h >>> >> >> Getting back to the namespaces ... >> In the current state the notifications will be sent to the init network namespace, >> which means that processes belonging to a different net namespace will not >> be able to receive them. To be more precise, those processes will not be >> able to subscribe to the multicast group, though this can be easily changed. >> Furthermore, the notifications might also be sent to specific namespace. >> In this case, the one, with which the trace for the mount point has been registered, >> which as I believe would be the best approach. >> >> As for the mount namespaces, reading the config file needs to be slightly tweaked, >> to hide away all the registered mount points which does not belong to the current >> mount namespace. >> >> Still, there is one possible 'issue' - the private/slave mount points. >> As the notifications will be sent to all the listeners (within the same netns), >> the events might be visible to processes outside the given mount ns. >> This should be limited to only those listeners that share the mount namespace, >> to which such private/slave mount points belong. As using the generic netlink >> to filter the outgoing messages is doable (with small changes to current >> implementation), the filters themselves seem rather cumbersome, as they would require >> finding the socket’s owner mount namespace, which just doesn't seems right. >> On the other hand, identifying the file system, which generated the event, will >> not be possible for processes outside such namespace, as device major:minor >> numbers are not bound to any namespace (afaict) so they will not provide any >> valid information. They will remain unresolved. >> >> The best way out here though, is to leave it to userspace to properly setup new namespaces: >> the mount namespace with possible private/slave mounts should have a separate >> network namespace to isolate the potential fs events, if required. >> >> >> BR >> Beata >> >> >> > > I'm not really sure where we are with this RFC now (?). > Just wanted to let You know I won't be available for the next two weeks, > in case this comes around. > > Best Regards > Beata > > Things has gone a bit quiet thread wise ... As I believe I've managed to snap back to reality, I was hoping we could continue with this? I'm not sure if we've got everything cleared up or ... have we reached a dead end? Please let me know if we can move to the next stage? Or, if there are any showstoppers? Thank You, Best Regards Beata -- 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/ . 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