Date: Wed, 29 Jul 2015 17:52:22 -0700 From: Laurie Jennings <laurie_jennings_1977@yahoo.com> To: John-Mark Gurney <jmg@funkthat.com> Cc: John Baldwin <jhb@freebsd.org>, freebsd-net@freebsd.org Subject: Re: Locking Memory Question Message-ID: <1438217542.41867.YahooMailBasic@web141502.mail.bf1.yahoo.com> In-Reply-To: <20150729232522.GN78154@funkthat.com>
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-------------------------------------------- On Wed, 7/29/15, John-Mark Gurney <jmg@funkthat.com> wrote: Subject: Re: Locking Memory Question To: "Laurie Jennings" <laurie_jennings_1977@yahoo.com> Cc: "John Baldwin" <jhb@freebsd.org>, freebsd-net@freebsd.org Date: Wednesday, July 29, 2015, 7:25 PM =20 Laurie Jennings via freebsd-net wrote this message on Wed, Jul 29, 2015 at 15:26 -0700: >=20 > I have a problem and I can't quite figure out where to look. This is what Im doing: >=20 > I have an IOCTL to read a block of data, but the data is too large to return via ioctl. So to get the data, > I allocate a block in a kernel module: > =20 > foo =3D malloc(1024000,M_DEVBUF,M_WAITOK); >=20 >=A0 I pass up a pointer and in user space map it using /dev/kmem: =20 An easier solution would be for your ioctl to pass in a userland pointer and then use copyout(9) to push the data to userland...=A0 This means the userland process doesn't have to have /dev/kmem access... =20 Is there a reason you need to use kmem?=A0 The only reason you list above is that it's too large via ioctl, but a copyout is fine, and would handle all page faults for you.. =20 __________________________________ I'm using kmem because the only options I could think of was to 1) use shared memory 2) use kmem 3) use a huge ioctl structure. Im not clear how I'd do that. the data being passed up from the kernel is a= variable size. To use copyout I'd have to pass a pointer with a static buffer, right? Is there a way to malloc user space me= mory from within an ioctl call? Or would I just have to pass down a pointer to a huge buffer large enough for = the largest possible answer? thanks Laurie
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