Date: Thu, 29 Apr 2010 22:28:31 +0200 (CEST) From: "=?ISO-8859-15?Q?Luk=E1=A8_Czerner?=" <czerner.lukas@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org, =?ISO-8859-15?Q?Luk=E1=A8_Czerner?= <czerner.lukas@gmail.com> Subject: Re: ioctl, copy string from user Message-ID: <alpine.DEB.1.10.1004292220170.30007@a04-0215a.kn.vutbr.cz> In-Reply-To: <201004291606.35899.jhb@freebsd.org> References: <alpine.DEB.1.10.1004291938210.30007@a04-0215a.kn.vutbr.cz> <201004291418.09768.jhb@freebsd.org> <alpine.DEB.1.10.1004292114360.30007@a04-0215a.kn.vutbr.cz> <201004291606.35899.jhb@freebsd.org>
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On Thu, 29 Apr 2010, John Baldwin wrote:
> > >
> > > On Thursday 29 April 2010 1:52:45 pm LukᨠCzerner wrote:
> > > > Hi,
> > > >
> > > > 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 mistake
> > > > I am not aware of. Please give me a hint if you can.
> > > >
> > > > What I want to do is simply call the ioctl from the userspace with
> > > > (char *) argument. Then, in kernel ioctl handling function copy the
> > > > string argument into the kernel space. I have tried it various ways,
> > > > everything without any success.
> > > >
> > > > *** Userspace ***
> > > > char name[MAXLEN];
> > > >
> > > > strncpy(name, argv[1], MAXLEN);
> > > > fprintf(stdout,"Name: %s\n",name);
> > > >
> > > > if (ioctl(fd, MYIOCTL, name)) {
> > >
> > > On BSD systems, ioctl() copies the data into the kernel for you ahead of
> time.
> > > What does the definition of MYIOCTL look like?
> >
> > #define MYIOCTL _IOW('M', 0, char *)
>
> 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
> userland to see if that fixes it.
I have already tried that, but still without any success. The buffer
remains unchanged (which is weird IMO).
Just FYI I am using FreeBSD-8.
>
> > > > And the second question. I have commented that I can allocate buffer
> > > > dynamically, but I suppose that there will be some locks involved so
> > > > I think I can not just use M_WAITOK, am I right ?
> > >
> > > malloc() and free() acquire their own locks internally, you do not need to
> > > hold any locks to call them.
> >
> > I probably does not express what I meant very clearly. My concern is
> > that when I am calling malloc with M_WAITOK I can sleep (be
> > rescheduled) and it may be bad thing if I am holding some lock,
> > because I can block others, am I right ?
>
> Generally yes, but it depends on the lock. If it is the vn_lock lock then it
> is ok to do a blocking malloc(). As a general rule I do try to call malloc()
> before acquiring locks (basically preallocating) whenever possible.
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.
Thanks.
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