December 2016 - kernelnewbies@kernelnewbies.org

Re: What's the purpose of subsys_interface in linux/device.h?
by Alexander Kapshuk Dec. 16, 2016

Dec. 16, 2016

On Fri, Dec 16, 2016 at 8:57 AM, Perr Zhang <strongbox8(a)zoho.com> wrote: > ---- On Fri, 16 Dec 2016 00:26:24 +0800 Alexander Kapshuk <alexander.kapshuk(a)gmail.com> wrote ---- > > > > Having looked at the pieces of source code below, it appears that > > subsys_interface is the means to expose specific functionality of a > > subsystem/class of devices, as the commentary below states. > > include/linux/device.h:331,350 > > /** > > * struct subsys_interface - interfaces to device functions > > * @name: name of the device function > > * @subsys: subsytem of the devices to attach to > > * @node: the list of functions registered at the subsystem > > * @add_dev: device hookup to device function handler > > * @remove_dev: device hookup to device function handler > > * > > * Simple interfaces attached to a subsystem. Multiple interfaces can > > * attach to a subsystem and its devices. Unlike drivers, they do not > > * exclusively claim or control devices. Interfaces usually represent > > * a specific functionality of a subsystem/class of devices. > > */ > > struct subsys_interface { > > const char *name; > > struct bus_type *subsys; > > struct list_head node; > > int (*add_dev)(struct device *dev, struct subsys_interface *sif); > > void (*remove_dev)(struct device *dev, struct subsys_interface *sif); > > }; > > > > Here's sample usage: > > arch/tile/kernel/sysfs.c:211,216 > > static struct subsys_interface hv_stats_interface = { > > .name = "hv_stats", > > .subsys = &cpu_subsys, > > .add_dev = hv_stats_device_add, > > .remove_dev = hv_stats_device_remove, > > }; > > > > And the add_dev method, whose main purpose seems to be creating a > > sysfs file for a particular device: > > arch/tile/kernel/sysfs.c:189,199 > > static int hv_stats_device_add(struct device *dev, struct subsys_interface *sif) > > { > > int err, cpu = dev->id; > > > > if (!cpu_online(cpu)) > > return 0; > > > > err = sysfs_create_file(&dev->kobj, &dev_attr_hv_stats.attr); > > > > return err; > > } > > > > Here's an example of the hv_stats_interface being registered with the subsystem: > > arch/tile/kernel/sysfs.c:261 > > err = subsys_interface_register(&hv_stats_interface); > > > > Hopefully, other members of this list will offer a better informed > > explanation than that given here. > > Sorry for sending email repeatedly. > I have also read the code: > device_add() -> bus_add_device() -> device_add_attrs(bus, dev) -> device_create_file(dev, &bus->dev_attrs[i]) > Since the attribute file/functionality could be added through bus->dev_attrs, why not to do it in this way? > My understanding is that an interface is like a protocol that has been put in place to enable a particular set of functions within a given subsystem or device model. I am sending a copy of this email to the list as well, so you can hopefully get a better informed reply to your query.

1 0

Website URL problem
by Amit Kumar Dec. 16, 2016

Dec. 16, 2016

Hi, I found this URL( http://janitor.kernelnewbies.org/) in LDD3 by Greg KH and others. But it takes to a page saying "This is the home machine of Rik van Riel." and there some links. I think there is something wrong with DNS settings. Regards, Amit Kumar

1 0

Kernel function sequence
by Wasim Akram Dec. 15, 2016

Dec. 15, 2016

How to know at what sequence , what function are being called when kernel starts ? Any way to trace what function calling what ... so on .? -- Thanks and Regards Wasim Akram

3 2

What's the purpose of subsys_interface in linux/device.h?
by Perr Zhang Dec. 15, 2016

Dec. 15, 2016

Hi, I am reading the code here: device_add()->bus_probe_device() the source code of bus_probe_device() is: void bus_probe_device(struct device *dev) { struct bus_type *bus = dev->bus; struct subsys_interface *sif; ...... mutex_lock(&bus->p->mutex); list_for_each_entry(sif, &bus->p->interfaces, node) if (sif->add_dev) sif->add_dev(dev, sif); mutex_unlock(&bus->p->mutex); } location: http://lxr.free-electrons.com/source/drivers/base/bus.c#L543 Problem: I have already read the relational code of struct subsys_interface, and can't figure out the purpose of struce subsys_interface and its method add_dev() Thank you, -- Perr

1 0

easiest way to deactivate a driver at boot time?
by Robert P. J. Day Dec. 15, 2016

Dec. 15, 2016

(Q asked by a colleague, a wee bit vague on details so i'm hoping i'm describing it correctly, seems like it should be easy to solve.) short form of question: what is the standard way of, at boot time, passing the kernel information to specify that a built-in driver should *not* be started? longer form of question: target system has two "slots", each of which contains a distinct embedded system running linux. both of those systems run the same kernel, *except* that, in slot 0, kernel should start and run a particular driver whereas, in slot 1, the kernel should *not* start that particular driver, whereupon apps on that system will fall back and do things differently. (apparently, the apps will use the simple existence of the driver's /dev/driver special device file to identify which approach to take.) as i understand it, then, whether or not that driver should start is based simply on being able to identify the slot the board is in, and this is something that is allegedly available to u-boot, which will then pass the appropriate info on the kernel command line, telling the kernel whether or not to start that driver. so far, so good. question is, what is the "appropriate" info to pass to the kernel to identify whether or not to start a (built-in) driver? my initial reaction was, define a simple module parameter, say "run", which is tested immediately upon driver startup, and if it's "0", just exit; otherwise, run normally. and then u-boot would add to the boot line: ... drivername.run=0 ... am i overthinking this? i'm used to module parameters being used to pass info to drivers and modules to *customize* their behaviour, not to simply say whether to run or not. is this a reasonable way to do this? is there a better/standard way? and is there a simple example of that in the current kernel source? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

4 5

Re: easiest way to deactivate a driver at boot time?
by Hayward, Shaun Dec. 15, 2016

Dec. 15, 2016

> On Dec 15, 2016, at 7:23 AM, Hayward, Shaun <haywshau(a)amazon.com> wrote: > > >> On Dec 15, 2016, at 4:59 AM, Robert P. J. Day <rpjday(a)crashcourse.ca> wrote: >> >> question is, what is the "appropriate" info to pass to the >> is this a reasonable way to do this? is there a better/standard way? >> and is there a simple example of that in the current kernel source? >> >> rday > > I just (last week) tackled a similar issue. In our case, we used u-boot to detect board type and then load a different device file. This caused our optional device to only be present on the appropriate board (we use udev). We also then used the device tree "model" name from user space to key additional customizations (/sys/firmware/devicetree/base/model, if memory serves me right). > > In this setup, the driver is always in the kernel (we run the same image for both boards), but a device is only registered on boards with the matching device in their device tree. > > Shaun (Forgot to cc list...)

1 0

What is this MODULE_ALIAS() used for?
by Perr Zhang Dec. 14, 2016

Dec. 14, 2016

source code: MODULE_ALIAS("platform:sm501"); static const struct of_device_id of_sm501_match_tbl[] = { { .compatible = "smi,sm501", }, { /* end */ } }; MODULE_DEVICE_TABLE(of, of_sm501_match_tbl); location: http://lxr.free-electrons.com/source/drivers/mfd/sm501.c#L1711 Since there is the MODULE_DEVICE_TABLE(), why the author additionally adds the MODULE_ALIAS()? What exactly is this MODULE_ALIAS() used for?

3 2

IDE for Kernel code browsing
by Madhu K Dec. 14, 2016

Dec. 14, 2016

Hi All, Anybody is using Kscope for kernel source code browsing?, if yes please share the information to enable fields present in "Query" tab. Thanks & regards, Madhu

1 0

Re: pls help in veth
by Er Krishna Dec. 13, 2016

Dec. 13, 2016

Thanks Rami for all the help. Yes lsmod shows that veth is not there. Perhaps the kernel has not been compiled with config_veth option enable in .config. Exact kernel version I will let you know tomorrow but most of the chances its 4.* kernel. Its customized kernel I got from different team, they have build it via yocto and I had to setup one network topology on it. BR/Krish On Tue, Dec 6, 2016 at 8:18 PM, Rami Rosen <roszenrami(a)gmail.com> wrote: > Hi Eri, > The driver is the veth driver, but it should be loaded automatically > when running this > command. > > What do you get when running: > > modprobe veth > > And what do you have when running > lsmod | grep veth ? > > Which kernel are you working with ? can you paste the output of > "uname -a"? is it a kernel you built from source, or a kernel which is > part of a distro? > > Regards, > Rami Rosen > http://ramirose.wix.com/ramirosen > > > > > > > > > > > On 6 December 2016 at 15:15, Er Krishna <erkrishna(a)gmail.com> wrote: > > Hi All, > > > > Can some one pls let me know for below command to run on linux which > driver > > and which package I need to install ? I see I have iproute package > installed > > on my box, but still I am facing below error. > > > > root@krishna:~# ip link add ep1 type veth peer name ep2 > > RTNETLINK answers: Operation not supported > > > > BR/Krish > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > >

2 3

Requesting for info about 15.4 network enabling...
by JANARDHANACHARI KELLA Dec. 12, 2016

Dec. 12, 2016

Hi to all, I am trying to enable 6lowpan network in raspberry pi.. I have built kernel with enabling 6lowpan network and drivers. I wish to route the devices from out side of the network... What I have to do? Please any one can help me, how to process... -- Sincerely Your's Janardhanachari Kella Contact:+91-9908469599 E-mail: eni.chari(a)gmail.com

1 0