Date: Thu, 29 Apr 2010 21:21:00 +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.1.10.1004292114360.30007@a04-0215a.kn.vutbr.cz> In-Reply-To: <201004291418.09768.jhb@freebsd.org> References: <alpine.DEB.1.10.1004291938210.30007@a04-0215a.kn.vutbr.cz> <201004291418.09768.jhb@freebsd.org>
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On Thu, 29 Apr 2010, John Baldwin wrote:
> Date: Thu, 29 Apr 2010 14:18:09 -0400
> From: John Baldwin <jhb@freebsd.org>
> To: freebsd-hackers@freebsd.org
> Cc: Lukáš Czerner <czerner.lukas@gmail.com>
> Subject: Re: ioctl, copy string from user
>
> On Thursday 29 April 2010 1:52:45 pm Lukáš Czerner 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 *)
>
> > 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 ?
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