On Wed, Jan 21, 2009 at 04:07:54PM +0200, Andriy Gapon wrote: > on 21/01/2009 15:55 Kostik Belousov said the following: > > On Wed, Jan 21, 2009 at 03:40:24PM +0200, Andriy Gapon wrote: > >> on 21/01/2009 15:35 Kostik Belousov said the following: > >>> On Wed, Jan 21, 2009 at 01:20:51PM +0200, Andriy Gapon wrote: > >>>> Question 1: > >>>> I am writing a driver that would use per-open private data (among other > >>>> features). > >>>> Do I have to use D_TRACKCLOSE flag in this case? > >>> No, the dtr registered with devfs_set_cdevpriv(), is called exactly once > >>> when the last close is performed, or the device is destroyed. > >> Kostik, > >> > >> thanks a lot for the explanation! > >> I am still a little bit confused about the term "last close" - what is > >> it? I.e. I'd like to get an answer to the below question. > >> > >>>> In general I am a little bit confused about when d_close is invoked. > >>>> Supposing D_TRACKCLOSE is not set and multiple programs concurrently > >>>> open, use and close a device - when d_close is called - when one program > >>>> closes its last descriptor tied to the device or when the system-wide > >>>> last such descriptor is closed? > > > > The kernel data structures for the opened device are as follows: > > > > filedesc ---> struct file ---> vnode ---> cdev > > [cdevpriv] \ / > > --------->----- > > > > Each -> arrow represents a "many to one" relation. There may be zero > > or one cdevpriv datum associated with struct file. > > > > cdev maintains the si_usecount, that is an accumulation of the vref > > counters for all devfs vnodes that are attached to the cdev. > > devfs_close() vop is called when the struct file is released. > > When D_TRACKCLOSE is specified, d_close driver method will be > > called unconditionally. > > When D_TRACKCLOSE is not specified, d_close is called when si_usecount > > is exactly 1, to become zero after the last close of the file that > > opened a vnode referencing cdev. > > Also, d_close() is called if the vnode is being reclaimed. Possible > > causes are revoke(2) call or forced devfs mp unmount. This interferes > > with close counting. > > > > cdevpriv dtr is called when either struct file is released, or > > device is destroyed by the destroy_dev(). > > Kostik, > > is the following true: if D_TRACKCLOSE is specified then a number of > d_close() calls and a number of cdevpriv dtr calls are equal (provide > each file gets cdevpriv data) ? > If not, what is the case where one is called but not the other?
No, I already described this. See the note about vnode reclamation. Also, d_close counter would have an interacation with destroy_dev(). To give you short summary, for D_TRACKCLOSE, d_close() may be called less times then dtr.
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