November 2011 - kernelnewbies@kernelnewbies.org

Locking IOCTL
by Praveen kumar Nov. 24, 2011

Nov. 24, 2011

Hi All, I have a situation where I have to lock the ioctl provided in my driver. I have a uni processor (ARM) system. I am using Mutex as the lock for my ioctl. DEFINE_MUTEX(&lock_ioctl); MyIoctl() { Mutex_lock(&lock_ioctl); Switch(){ ........... } Mutex_unlock(&lock_ioctl); return 0; } I just wanted to know am I using the best lock available for the situation aor do I have any flaw in my implementation??? And from LKD I read that "*lock the data not the code*" and which I am literally doing so ?? any comments on this ? I have interrupts in my driver which is nothing to do with the lock.I am taking care that where ever I return in my ioctl the lock is released. Thanks , Praveen

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busybox utility
by naveen yadav Nov. 24, 2011

Nov. 24, 2011

Dear all, I am checking busybox utility, Is there any other package available similar to busybox which we can use in embedded system . Thanks

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Re: busybox utility
by naveen yadav Nov. 24, 2011

Nov. 24, 2011

Hi All, Thanks for your answer. I want to know is there any similar package like busybox we can use in embedded product. I found few of them but could not found as good as busybox. so this is reason i ask. 1. http://www.fefe.de/embutils/ 2. https://github.com/asdf-systems/gobox 3. http://www.landley.net/code/toybox/about.html For security issue in busybox. I could not find detail but below slide mention it . https://speakerd.s3.amazonaws.com/presentations/4e9334432deb290054011ba7/sl… Thanks On Wed, Nov 23, 2011 at 4:30 PM, Bernd Petrovitsch <bernd(a)petrovitsch.priv.at> wrote: > On Mit, 2011-11-23 at 10:42 +0530, Mandeep Sandhu wrote: >> > I post on Kernel newbies since i could not found any good place to post. > > Why this not good place and not one of the other not good places? > It's about newbies to the (Linux) kernel as such after all (and not > about "Linux newbies"). > There probably more people on the busybox list or embutils ML (is there > one?) who know about "competing products" (what's the socially accepted > term nowadays for that?). > >> > We do not want to use busybox due to its licence and security issue. > > For the license part: Well, tough luck. What's the problem with GPLv2? > > Perhaps Google finds a similar package with another - proprietary? - > license. > There are lots of companies out there, there should be several to choose > a vendor. > >> What security issue are you concerned about? Can you explain your >> concern a little more. >> >> Also, if you have some busybox specific question, ppl on the busybox >> mailing list will be able to help you better. > > For the security part: the busybox list would be eager to hear of any > problems so that one can fix them. > > Bernd > -- > Bernd Petrovitsch Email : bernd(a)petrovitsch.priv.at > LUGA : http://www.luga.at > >

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Ownership of sk_buff
by Vimal Nov. 24, 2011

Nov. 24, 2011

Hi all, When a protocol like TCP or UDP creates an sk_buff and passes it down to the layer 3 and layer 2 protocol functions, which module has ownership of the buffer as it gets passed down? Is it the responsibility of the caller, or the callee to free the sk_buff? Are there any exceptions? Thanks, -- Vimal

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GPL-only symbol Error
by Sengottuvelan S Nov. 23, 2011

Nov. 23, 2011

Hi All, Basically, I am developing a kernel module named "xyz.ko" and my MODULE_LICENSE is "Proprietary". I have got an error "GPL-incompatible module xyz.ko uses GPL-only symbols". I am having trouble identifying it. How to avoid this error in during MODPOST?. Is there any way to avoid this error? Can you someone throw light on this. Regards, S. Sengottuvelan.

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RE: GPL-only symbol Error
by Jeff Haran Nov. 23, 2011

Nov. 23, 2011

> -----Original Message----- > From: Bernd Petrovitsch [mailto:bernd@petrovitsch.priv.at] > Sent: Wednesday, November 23, 2011 2:51 AM > To: Sengottuvelan S > Cc: Graeme Russ; Greg KH; Kernel Newbies; Jeff Haran > Subject: RE: GPL-only symbol Error > > On Die, 2011-11-22 at 17:21 -0800, Jeff Haran wrote: > [....] > > Perhaps, but that's not what I asked about. It seems to me the essence > > of GPL is that it grants people the right to modify GPL sources like > > the Linux kernel in any way they want so long as they make those > > changes available to whoever uses the code in the future. I don't see > > You forgot that you also have the hand out the same rights you have to > other people with the (changed) source. > You forgot that all of that also holds for all of your changes, removal > and additions to that code (and lawyers don't care if the changes good, > bad or ugly). Which is what I suggested in the hypothetical scenario I described. The change to the kernel source to change an EXPORT_SYMBOL_GPL() to EXPORT_SYMBOL() would be published. > > anything in it that prohibits specific changes. So if I take a symbol > > that in the sources from kernel.org is declared with > > EXPORT_SYMBOL_GPL(), make a 1 line change that declares it > > EXPORT_SYMBOL() and put that on a publically available web site, how > > have I violated GPL? > > IANAL (and there are pretty much no non-lurking lawyers on LKML), but > you probably didn't violate the GPL as such on the kernel you downloaded > with such a change. But that hasn't anything to do with the legal side - > ask a lawyer if can change the legal "status" with such a change. Just to be clear, I haven't done any of this. This thread originated with somebody else asking why he was getting this build error when he attempted to build his non-GPL module that referenced EXPORT_SYMBOL_GPL() exported symbols. I was attempting to explain to that original poster why he was getting the error. > > Let's say I then ship a product that uses that custom kernel and a > > non-GPL kernel module of my own writing that only works with the > > custom kernel, how is that prohibited in the GPL license? > > That's the actual bug: You assume that you can legally make a > proprietary Linux kernel module by simply declaring to do so (and going > deeper is not quite possible as we do not know the module ....). I can clearly legally write a user space program that results in calls to kernel symbols without publishing it. To do that I load parameters into registers and onto the stack and issue a trap to generate a system call. A kernel module does almost the same thing, except instead of generating a trap, it makes a more traditional function call. The difference is technical and I don't see anything in the COPYING file that makes any reference to this difference. If I have missed that verbiage in the license, please point it out to me. > Than you stumbled on a warning to help you to realize that (and not > hitting such warnings or plain simply removing them doesn't change > anything on the legal side IMHNLO). > And you think you can "fix" the warning by simply removing it (ignoring > the underlying issue). Again, it I didn't stumble on this warning. The original poster did. All I did was respond to a post on a public email list. > But your kernel module is very probably a derived work of the Linux > kernel anyway and thus automatically and implicitly GPL (even if your > whole company may want it, has been told or think otherwise). "very probably a derived work". That is a big assumption. What in the license defines all code that makes calls into kernel symbols via the dynamic module loader mechanism different than code that calls into that code via a trap? > > Not that I am planning on doing this and I've never done it in the > > past, but technically it seems that there would be no violation here. > > Technically, your module is a derived work of the Linux kernel unless > proven otherwise. Again, not my module, not my company's module. I was simply answering a post to this email list and asking questions around a hypothetical scenario. Jeff Haran

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issues regarding using initramfs for entire root fs?
by Robert P. J. Day Nov. 23, 2011

Nov. 23, 2011

i figure someone here has probably done this -- just as proof-of-concept, i want to create a kernel that incorporates a standalone initramfs root filesystem. if it's useful to know, it will be for a powerpc lite5200 board. it's not something i'd do in normal practice, but it's for a course i'm teaching in a couple weeks, and i thought it would be fun to show how it works. i've never done it myself, so i just want to know what limits or issues i'd run into, such as a hard limit on initramfs size or anything else. obviously, i'll try to build as small an initramfs as possible. as i said, it's not meant to be practical so much as just a demo of it being a possibility. rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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Re: busybox utility
by Thomas Petazzoni Nov. 23, 2011

Nov. 23, 2011

Le Wed, 23 Nov 2011 13:58:13 +0100, Bernd Petrovitsch <bernd(a)petrovitsch.priv.at> a écrit : > IIUC, that .pdf are just *marketing*/*sales* slides where the GoBox > folks basically tell everyone that BusyBox is "bad" (because it is > "huge") and GoBox is "good" (because it is allegedly small). I fully agree here. Those slides are pretty. But that's about the only thing that is nice with those slides. The contents is complete bullshit with no facts to back the statements made in those slides. Just don't trust everything you read on the Internet. Especially things written by marketing people. And again, as asked by Bernd, could you expand on what your problem is with GPLv2 ? Remember that the Linux kernel itself is under GPLv2. Regards, Thomas -- Thomas Petazzoni, Free Electrons Kernel, drivers, real-time and embedded Linux development, consulting, training and support. http://free-electrons.com

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how set_user_nice() function is called
by Enes Albay - انس الباى Nov. 23, 2011

Nov. 23, 2011

Hi! anybody knows that where is set_user_nice() function called in the kernel? i couldn't find that. i just found that in forking operation do_fork()->copy_process()-> dup_task_struct() called then set_user_nice() called but i couldn't find that where. Also how/where do_fork() function called in kernel i couldn't find. Thanks in advance... -- Enes Albay

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plz help with the serial port pgm....
by shibin k reeny Nov. 23, 2011

Nov. 23, 2011

rs232 read pgm is not working when i connect in loopback but write is wroking plz help... pgm #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <fcntl.h> #include <termios.h> #define _POSIX_SOURCE 1 #define BAUDRATE B9600 #define MODEMDEVICE "/dev/ttyS1" int main(void) { int ret, fd; struct termios tio; char buf[255]; /* Open device for reading and writing */ fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NDELAY); if (fd < 0) { fprintf(stderr, "Error opening device %s\n", MODEMDEVICE); goto done; } /* get current port attributes */ ret = tcgetattr(fd, &tio); if (ret < 0) { fprintf(stderr, "Error retreiving attributes, ret=%d\n", ret); goto done; } tcflush(fd, TCIFLUSH); /* set port input speed */ ret = cfsetispeed(&tio, BAUDRATE); if (ret) { fprintf(stderr, "Error setting input Baud rate, ret=%d\n", ret); goto done; } /* set port output speed */ ret = cfsetospeed(&tio, BAUDRATE); if (ret) { fprintf(stderr, "Error setting output Baud rate, ret=%d\n", ret); goto done; } tio.c_cflag &= ~CRTSCTS; /* HW flow ctl OFF */ tio.c_cflag &= ~PARENB; /* no parity */ tio.c_cflag &= ~CSTOPB; /* 1 stop bit */ tio.c_cflag &= ~CSIZE; /* 1 stop bit */ tio.c_cflag |= CS8; /* char size; 8N1 */ tio.c_cflag |= CREAD; /* enable receiver */ /* set port attributes */ ret = tcsetattr(fd, TCSANOW, &tio); if (ret < 0) { fprintf(stderr, "Error setting attributes, ret=%d\n", ret); goto done; } fcntl(fd, F_SETFL, FNDELAY); ret = write(fd, "ab\r", 3); if (ret < 0) fprintf(stderr, "write() of 3 bytes failed!, ret=%d\n", ret); printf("no of data written = %d\n",ret); usleep(5000); while (1) { ret = read(fd, buf, sizeof(char)); if (ret > 0) { printf("%c",buf[0]); } } done: close(fd); return 0; } ################################## output../a.out no of data written = 3 ######################## strace ./a.out read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable) read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily unavailable)

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