Date: Tue, 28 Aug 2012 12:40:29 -0400 From: John Baldwin <jhb@freebsd.org> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: freebsd-current@freebsd.org, current@freebsd.org, Andriy Gapon <avg@freebsd.org> Subject: Re: per file descriptor device callbacks ? Message-ID: <201208281240.29612.jhb@freebsd.org> In-Reply-To: <20120828155025.GA66068@onelab2.iet.unipi.it> References: <20120827073403.GA49223@onelab2.iet.unipi.it> <201208271227.54785.jhb@freebsd.org> <20120828155025.GA66068@onelab2.iet.unipi.it>
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On Tuesday, August 28, 2012 11:50:25 am Luigi Rizzo wrote: > On Mon, Aug 27, 2012 at 12:27:54PM -0400, John Baldwin wrote: > > On Monday, August 27, 2012 3:55:47 am Andriy Gapon wrote: > > > on 27/08/2012 10:34 Luigi Rizzo said the following: > > > > This requires to track calls to open/ioctl/poll/mmap/close. > > > > The difficulty i have is with mmap() and close(), because FreeBSD > > > > seems to handle these calls per-cdev rather than per-file-descriptor > > > > (for instance, no 'struct file' argument is available in mmap(), and > > > > the d_close method is only called on the last close() on the device). > > > > > > devfs_set_cdevpriv(9), etc > > > > mmap() is still problematic, but if you have the freedom to create your > > own VM objects, then d_mmap_single() can let you handle that fairly > > easily. > > Would dev_clone(9) be a better way to do what i need ? > > This way the struct cdev would be unique per file descriptor, > could be used as a key on the page fault callbacks > (i still do not have callbacks on dev_pager_ctor/dtor though). dev_clone() is rather gross and a lot harder to use than devfs_set_cdevpriv(). If you are fine with the inherent problems of the device pager (you can't ever make mappings go away), you can just assign each client a unique offset into your shared object's memory space. However, if you are exporting shared memory buffers, then a better model might be to let your clients use shm_open(SHM_ANON) to create buffers, then pass them into your driver via an ioctl() and use shm_map() to map them into the kernel. -- John Baldwin
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