Date: Thu, 29 Apr 2010 16:56:12 -0400 From: John Baldwin <jhb@freebsd.org> To: "=?iso-8859-15?q?Luk=E1=A8?= Czerner" <czerner.lukas@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: ioctl, copy string from user Message-ID: <201004291656.12565.jhb@freebsd.org> In-Reply-To: <alpine.DEB.1.10.1004292220170.30007@a04-0215a.kn.vutbr.cz> References: <alpine.DEB.1.10.1004291938210.30007@a04-0215a.kn.vutbr.cz> <201004291606.35899.jhb@freebsd.org> <alpine.DEB.1.10.1004292220170.30007@a04-0215a.kn.vutbr.cz>
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On Thursday 29 April 2010 4:28:31 pm Luk=E1=A8 Czerner wrote:
> On Thu, 29 Apr 2010, John Baldwin wrote:
> > > >=20
> > > > On Thursday 29 April 2010 1:52:45 pm Luk=E1=A8 Czerner wrote:
> > > > > Hi,
> > > > >=20
> > > > > I know that there are plenty of examples in the kernel code, but I
> > > > > just can not get it working, so maybe I am doing some stupid mist=
ake
> > > > > I am not aware of. Please give me a hint if you can.
> > > > >=20
> > > > > What I want to do is simply call the ioctl from the userspace with
> > > > > (char *) argument. Then, in kernel ioctl handling function copy t=
he
> > > > > string argument into the kernel space. I have tried it various wa=
ys,
> > > > > everything without any success.
> > > > >=20
> > > > > *** Userspace ***
> > > > > char name[MAXLEN];
> > > > >=20
> > > > > strncpy(name, argv[1], MAXLEN);
> > > > > fprintf(stdout,"Name: %s\n",name);
> > > > >=20
> > > > > if (ioctl(fd, MYIOCTL, name)) {
> > > >=20
> > > > On BSD systems, ioctl() copies the data into the kernel for you ahe=
ad of=20
> > time. =20
> > > > What does the definition of MYIOCTL look like?
> > >=20
> > > #define MYIOCTL _IOW('M', 0, char *)
> >=20
> > Ok. In that case the argument to ioctl needs to be a pointer to a char=
*,
> > not the raw char * itself. Try doing 'ioctl(fd, MYIOCTL, &name)' from=
=20
> > userland to see if that fixes it.
>=20
> I have already tried that, but still without any success. The buffer
> remains unchanged (which is weird IMO).
Can you print out the value of 'ap->a_data' from the kernel and the value of
'&name' in userland?
> > Generally yes, but it depends on the lock. If it is the vn_lock lock t=
hen it=20
> > is ok to do a blocking malloc(). As a general rule I do try to call ma=
lloc()
> > before acquiring locks (basically preallocating) whenever possible.
>=20
> So I suppose M_NOWAIT will do the trick when there is no other way
> (preallocations etc..) ? Of course I should test if it does not
> return NULL then.
Yes, but in a VOP_IOCTL() handler it should be safe to M_WAITOK malloc() as
long as you do it before you acquire any mutexes.
=2D-=20
John Baldwin
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