Date: Mon, 9 May 2011 10:35:07 -0500 From: Alan Cox <alan.l.cox@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-current@freebsd.org, Andriy Gapon <avg@freebsd.org>, multimedia@freebsd.org Subject: Re: dsp mmap change Message-ID: <BANLkTin%2B6zvOnNk67f93pFO%2BA=VZPmWw%2BQ@mail.gmail.com> In-Reply-To: <201105090945.05130.jhb@freebsd.org> References: <4DC3B764.4030801@FreeBSD.org> <201105061616.41145.jhb@freebsd.org> <20110507191625.GQ48734@deviant.kiev.zoral.com.ua> <201105090945.05130.jhb@freebsd.org>
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On Mon, May 9, 2011 at 8:45 AM, John Baldwin <jhb@freebsd.org> wrote: > On Saturday, May 07, 2011 3:16:25 pm Kostik Belousov wrote: > > On Fri, May 06, 2011 at 04:16:40PM -0400, John Baldwin wrote: > > > On Friday, May 06, 2011 10:04:28 am Kostik Belousov wrote: > > > > On Fri, May 06, 2011 at 04:38:00PM +0300, Andriy Gapon wrote: > > > > > on 06/05/2011 16:32 Kostik Belousov said the following: > > > > > > On Fri, May 06, 2011 at 11:55:00AM +0300, Andriy Gapon wrote: > > > > > >> > > > > > >> I would like to ask for a review and/or testing of the following > patch: > > > > > >> http://people.freebsd.org/~avg/dev_dsp_mmap.diff > > > > > >> > > > > > >> It's supposed to fix an issue described here: > > > > > >> http://lists.freebsd.org/pipermail/freebsd-multimedia/2011- > > > February/011691.html > > > > > >> > > > > > >> In short, the following pseudo-code should do the right thing: > > > > > >> fd = open(/dev/dsp, O_RDWR); > > > > > >> mmap(PROT_READ, fd); > > > > > >> mmap(PROT_WRITE, fd); > > > > > >> > > > > > >> Thank you! > > > > > > > > > > > > I think that you have to call PCM_GIANT_LEAVE() when returning > > > > > > EINVAL on the vm_pager_alloc() failure. > > > > > > > > > > Yes, thank you. > > > > > > > > > > > Your patch hardcodes an assumption that sndbufs are always > > > > > > contiguous. I was unable to convince myself that this is true. > > > > > > > > > > I think that this should be true for the case when DMA is used? > > > > In the current driver, yes, but there is nothing that theoretically > > > > prevents scatter-gather from be used. > > > > > > You could "fix" this by creating an sglist (via sglist_build()) and an > > > OBJT_SG VM object that the d_mmap_single callback returned. I wish > there > > > was a cleaner way to just create a VM object and populate it with pages > > > though, and then use vm_map_insert() to map it into the kernel rather > > > than the more roundabout method of OBJT_SG. > > > > You cannot have one page inserted into two vm objects. Contigmalloc() > > inserts the allocated pages into kernel_object. > > Yes, I would want to allocate N unmapped pages and stuff them into a VM > object that can then be mapped into the kernel and/or into user mappings. > This would be a much cleaner approach for the nvidia driver for example. > > There is a relatively new function, vm_object_populate(), that allocates a collection of pages, inserts them into a vm object, and validates them for use. This function exits in FreeBSD 7.x, 8.x, and HEAD. Alan
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