February 2015 - kernelnewbies@kernelnewbies.org

Re: Overlapping regions in DT
by Stefan Wahren Feb. 11, 2015

Feb. 11, 2015

Hi Tsahee, Am 09.02.2015 um 09:22 schrieb Tsahee Zidenberg: > syscon regmap is one possible way to access a register file from two > different drivers without mapping it twice. But in that case you loose > the name-per-register in devicetree. The devtree maps the general > regfile, and the drivers know the offsets by themselves. > Have a look here: > Have a look: http://thread.gmane.org/gmane.linux.kernel/1352299 thanks for your suggestion. I'll give it a try. Stefan

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Is this a good first patch for enabling screen rotation?
by Brock York Feb. 11, 2015

Feb. 11, 2015

Hello This is my first patch and after speaking to a few kernel devs at LCA2015 I thought I would ask here for some advice on if I have followed the newbie guide correctly. The patch is to get automatic screen rotation working on a acer iconia w500 tablet. The patch was made against linux-next branch next-20150129 and successfully built and ran. Do you think this is a succificient patch to get accepted by the platform-x86 maintainers? I used get_maintainer.pl and it suggested the platform-x86 mailing list. Thank you, any help is much appreciated. Regards Brock York. BEGIN PATCH BELOW------------ Subject: [PATCH] acer-wmi: Enable screen auto-rotation via udev Emit udev event via kobject_uevent when accelerometer position is updated. This is to allow userspace to grab the accelerometer position and rotate the screen accordingly. Swap the x and y values and negate the x value converting the accelerometers coordinate system into the coordinate system userspace udev expects. Accelerometer Expected Coordinates Coordinates x+ y+ ^ ^ | | | | y+<----/ /---->x+ / / z+ z+ Screen Orientation ________ | | | | |________| Tested on a Acer Iconia W500 tablet with Gnome 3 Signed-off-by: Brock York <twunknown(a)gmail.com> --- drivers/platform/x86/acer-wmi.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/platform/x86/acer-wmi.c b/drivers/platform/x86/acer-wmi.c index 3ac29a1..d5678e4 100644 --- a/drivers/platform/x86/acer-wmi.c +++ b/drivers/platform/x86/acer-wmi.c @@ -1491,12 +1491,14 @@ static int acer_gsensor_event(void) return -1; input_report_abs(acer_wmi_accel_dev, ABS_X, - (s16)out_obj->package.elements[0].integer.value); + -(s16)out_obj->package.elements[1].integer.value); input_report_abs(acer_wmi_accel_dev, ABS_Y, - (s16)out_obj->package.elements[1].integer.value); + (s16)out_obj->package.elements[0].integer.value); input_report_abs(acer_wmi_accel_dev, ABS_Z, (s16)out_obj->package.elements[2].integer.value); input_sync(acer_wmi_accel_dev); + + kobject_uevent(&acer_wmi_accel_dev->dev.kobj, KOBJ_CHANGE); return 0; } -- 2.2.2

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Wireless, how to use dual band
by Robert Clove Feb. 11, 2015

Feb. 11, 2015

Hi, I have few laptops and two routers with dual band (TP-LINK TL-WDR3600 N600 WIRELESS DUAL BAND GIGABIT ROUTER) . What i am trying to achieve is if someone want to send msg to a an individual then one of the band should be used (eg 2.4GHz) and if someone want to send message to the group then it should be send through another band (eg 2.8GHz or 5 GHz). How can i do that.? I have created a mesh network and written a simple client server applications through which all laptops communicate. Sorry if this is not the correct mailing list Regards

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Is writer starvation a potential problem with RCU?
by Jeff Haran Feb. 9, 2015

Feb. 9, 2015

I've read that the Linux implementation of read-write locks (rwlock_t) can suffer from so called "writer starvation", whereby threads that take a read lock on a read-write lock can prevent threads attempting to take a write lock on the same read-write lock from ever acquiring the lock because there is no queuing of the readers and writers. If the lock is held for read access, any subsequent reader will get the lock even if a write lock attempt is already in progress. Does anybody happen to know whether or not RCU has a similar issue? Thanks, Jeff Haran

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Overlapping regions in DT
by Stefan Wahren Feb. 8, 2015

Feb. 8, 2015

Hi, currently i work on two DT capable drivers for a ARM9 processor. The former driver mxs_power.c should trigger the population of the underlying power management functions and the ladder take care of the on-chip regulators. In the future more drivers should be added as child nodes of the power driver. My problem is that some of the processor registers are not separated per function. So the drivers need access (mostly read) on the same registers. Here are my questions: How should define i the register space in the device? Define the regions in the parent node and use offsets in the childs? Which functions are recommend for such access? I want to make use of of_platform_populate / of_platform_depopulate. Is there anything i should take care of? The relevant parts of the devicetree is at the end of the mail. Best regards Stefan power: power@80044000 { compatible = "fsl,imx28-power"; /* handled by mxs_power.c */ #address-cells = <1>; #size-cells = <1>; reg = <0x80044000 0x2000>; interrupts = <6>; ranges; reg_vddd: regulator@80044040 { reg = <0x80044040 0x10>, <0x80044010 0x10>, <0x800440c0 0x10>; reg-names = "base-address", "v5ctrl-address", "status-address"; compatible = "fsl,imx28-vddd"; /* handled by mxs-regulator.c */ regulator-name = "vddd"; regulator-min-microvolt = <1350000>; regulator-max-microvolt = <1550000>; vddd-supply = <&reg_vdda>; }; reg_vdda: regulator@80044050 { reg = <0x80044050 0x10>, <0x80044010 0x10>, <0x800440c0 0x10>; reg-names = "base-address", "v5ctrl-address", "status-address"; compatible = "fsl,imx28-vdda"; /* handled by mxs-regulator.c */ regulator-name = "vdda"; regulator-min-microvolt = <1725000>; regulator-max-microvolt = <1950000>; vdda-supply = <&reg_vddio>; }; reg_vddio: regulator@80044060 { reg = <0x80044060 0x10>, <0x80044010 0x10>, <0x800440c0 0x10>; reg-names = "base-address", "v5ctrl-address", "status-address"; compatible = "fsl,imx28-vddio"; /* handled by mxs-regulator.c */ regulator-name = "vddio"; regulator-min-microvolt = <3000000>; regulator-max-microvolt = <3575000>; regulator-microvolt-offset = <80000>; }; };

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Re: Question about kernel interfaces
by Siddhartha De Feb. 7, 2015

Feb. 7, 2015

>(For bonus points, instead of EJECT, explain how you form a curl URL >that does TCSETS. Yes, you *do* have to handle *all* the fields of a >struct termios, for both 32 and 64 bit environments....) I am new to termios programming so please correct me if I am wrong ... I did a bit of googling and well here's a probable curl url and the corresponding pseudocode that needs to be in our interpreter curl http://localhost:7000/IOCTL/TCSETS2?file_descriptor=fd&cflag=something&ispe… And here's a little pseudocode for our interpreter :- struct termios2 tio; // ioctl(fd, TCGETS2, &tio); // assuming get_from_url is a function which parses the incomming url and returns the required parameters cflag=get_from_url (cflag ) ; ispeed = get_from_url ( ispeed ) ; ospeed=get_from_url(ospeed) tio.c_cflag = cflag ; tio.c_ispeed = ispeed; tio.c_ospeed = ospeed; ioctl(fd, TCSETS2, &tio); Thanking you in anticipation , Yours sincerely , Kernel newbie On Wed, Jan 21, 2015 at 11:14 PM, One Thousand Gnomes <gnomes(a)lxorguk.ukuu.org.uk> wrote: > On Sun, 18 Jan 2015 15:03:55 +0530 >> Let's say you need to call an ioctl from a shell script ( I know its a >> very rare use case but please bear with me ... :) ) >> >> So the current way of doing it is probably to write a C program which >> actually calls the ioctl and then call the C program from the shell >> script ... > > That's how Unix is designed yes. It means that the ioctl internals are > hidden from the scripts and the tools provided can be used instead. > >> and the IOCTL_EJECT ioctl would get called on /dev/cdrom >> that is ioctl ( &handle_to_/dev/cdrom , IOCTL_EJECT , &some_buffer ) >> would get called ( by our translator running as a separate program or >> as a service daemon ) > > You can just run "eject". It knows about all the details of doing an > eject. > > The equivalent of a "library" in shell scripts is a program. Small, > simple tools that do one job and do it right, or at least before GNU got > hold of them 8) > > Alan

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Fwd: Getting path in inode_permission
by noyb noybee Feb. 7, 2015

Feb. 7, 2015

On Sat, Feb 7, 2015 at 4:21 AM, <Valdis.Kletnieks(a)vt.edu> wrote: > On Sat, 07 Feb 2015 01:57:44 +0530, noyb noybee said: >> I need the path lookup data as I need to specifically block inode >> loopkups originating from a certain path > > Then just make sure the inodes you don't want accessed aren't in the > namespace. > > Hint: "from a certain path" is almost guaranteed to be a security hole, > because all the attacker has to do is cwd() to some different path. And > there's ../ games that can be played, and so on. > > So what are you trying to protect by blocking some lookups? What's the > threat model here? I am trying to enhance the security features of the chroot "jail"(I know it wasn't built for the purpose). I am trying to prevent access to files outside the "jail" unless they specify a specific passsphrase. Whenever an inode is accessed, inode_persmission is called. I get the pid of the calling process by current->pid in the hook and check if it is a child of the original process for which chroot was run. If yes + if this process hasn't specified a passphrase + the path of the inode shows that it is outside the "jail", the request is blocked. I am also blocking all mounts in the "jail". Regards, winged_elite.

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Getting path in inode_permission
by noyb noybee Feb. 6, 2015

Feb. 6, 2015

I need the path lookup data as I need to specifically block inode loopkups originating from a certain path(hence the permission mask is not enough). Is there a way to get it from inside the inode_permission hook or is there another hook I can use(not file_permission since I want the hook for any kind of access, not just read/writes) ? Regards, winged_elite

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mount namespace + d_path question
by David Legault Feb. 6, 2015

Feb. 6, 2015

Hello, Question regarding pathnames and mount namespaces. As I understand mount namespaces enable different processes to mount filesystems at different locations leading to different paths to the same underlying file. When you do something like the below in kernel code: d_path(&file->f_path, filename, PATH_MAX+11); How can you guarantee that the returned full path is against the root/init mount namespace instead of the calling process' mount namespace? Thanks David

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eudyptula response time
by Dean Michael Ancajas Feb. 6, 2015

Feb. 6, 2015

Hi, does anyone have an idea when is the response time for task 08? When I submitted last december, I was 115th in the queue. I don't want to resubmit again fearing that I will be bumped up into the end. Dean

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