On Wed, Apr 29, 2015 at 05:48:14PM +0200, Beata Michalska wrote: > On 04/29/2015 03:45 PM, Greg KH wrote: > > On Wed, Apr 29, 2015 at 01:10:34PM +0200, Beata Michalska wrote: > >>>>> 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? > >> > >> AFAIK, for such filesystems there will be similar case with the anonymous > >> major:minor numbers - at least the btrfs is doing so. Not sure we can > >> differentiate here the actual block device. So in this case such events > >> serves merely as a hint for the userspace. > > > > "hint" seems like this isn't really going to work well. > > > > Do you have userspace code that can properly map this back to the "real" > > device that is causing problems? Without that, this doesn't seem all > > that useful as no one would be able to use those events. > > I'm not sure we are on the same page here. > This is about watching the file system rather than the 'real' device. > Like the threshold notifications: you would like to know when you > will be approaching certain level of available space for the tmpfs > mounted on /tmp. You do know you are watching the /tmp > and you know that the dev numbers for this are 0:20 (or so). > (either through calling stat on /tmp or through reading the /proc/$$/mountinfo) > With this interface you can setup threshold levels > for /tmp. Then, once the limit is reached the event will be > sent with those anonymous major:minor numbers. > > I can provide a sample code which will demonstrate how this > can be achieved. Yes, example code would be helpful to understand this, thanks. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
