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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This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-1225407102-1272568861=:30007 Content-Type: TEXT/PLAIN; charset=utf-8 Content-Transfer-Encoding: 8BIT 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 ? --8323329-1225407102-1272568861=:30007--
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