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. BR 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>