February 2015 - kernelnewbies@kernelnewbies.org

How to handle Hotplug with UIO userspace driver
by Mandeep Sandhu Sept. 28, 2017

Sept. 28, 2017

Hi All, We're working on a custom PCIe based hardware, which can be hotplugged into the system. We're using the UIO approach of having a minimal kernel driver which basically handles the interrupt and provides a mmap of the device memory to userspace and userspace driver which mmap's the provided memory and manages the device. We're using systemd and udev rules to spawn off a user process whenever the hardware is plugged into the system. Now my question is, how can we gracefully inform the userspace process if someone pulls out the hardware (sitting on a PCI slot). Even with full hotplug support, there can always be a case of "surprise removal", where someone yanks the board without going through the whole "attention button" routine. While the kernel driver has no problem with hot-removal, I see that if I "unregister" our UIO driver in response to the removal, then the mapping for the hardware's physical memory would become "invalid" (done by UIO on unregsiter). This could possibly cause the user-space process to crash due to illegal memory access. Is there a "standard" way to handle this scenario, i.e for hotpluggable hardware using UIO? Basically, we'd want to "unregister" the UIO device only after the userspace process is informed of the removal so that it could unmap/close the device and exit gracefully. We could try doing it using some systemd trick, where we put a dependency on one of the UIO created files (/dev/uioX), so that when the file is destroyed, systemd could kill/shutdown the process. Although, there's no guarantee that the userspace process won't try to access the mmaped space during that interval, so this isn't a reliable solution either. Any hints, thoughts? Thanks., -mandeep

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How to get the inode - no path_lookup
by Rishi Agrawal Sept. 17, 2015

Sept. 17, 2015

Hi All, I had a module which used the path_lookup function to print the details of any file's inode. I now want to rewrite that module in order to show some juniors how to write some code in kernel. I am using 3.4.6 kernel, I tried finding out path_lookup but google showed that it has been removed. I tried the following code then which did not work . . . dentry = kern_path_create(AT_FDCWD, filename, &path, 1); if (IS_ERR(dentry)) { printk("Failed to obtain the dentry"); return; } its not returning dentry I again tried after seeing the implementation of vfs_stat function user_path_at(AT_FDCWD, filename, lookup_flags, &path); but this also fails. I am using a proc interface to pass the filename, and copying the filename into a kernel buffer. How can I get a copy of vfs inode for a file name. -- Regards, Rishi Agrawal

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Eudyptula challenge task 6 reply
by harshkdev May 5, 2015

May 5, 2015

Hi all, I have sent solution of task 6 on 8/feb/2015.Till now didn't get reply.Do I resend the email or wait. I thought eudyptula is ignoring the reply. Regards Harsh Jain

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Is it all right for Netfilter modules to use control buffers (skb->cb)?
by Alberto Leiva April 28, 2015

April 28, 2015

Hi I was assuming yes, since I've seen at least one module doing this. An example is nf_defrag_ipv6 (ipv6_defrag() calls nf_ct_frag6_gather() which calls NFCT_FRAG6_CB()). What confuses me is that the IPv6 subsystem seems to have its own control buffer: - ipv6_rcv() calls IP6CB(): http://lxr.free-electrons.com/source/net/ipv6/ip6_input.c?v=3.17#L102 - then it calls the netfilter chain, which might include nf_defrag_ipv6: http://lxr.free-electrons.com/source/net/ipv6/ip6_input.c?v=3.17#L186 - then ip6_rcv_finish() comes into play, which calls dst_input(), which might well call ip6_input(), which calls ip6_input_finish(). - ip6_input_finish() once again dereferences the IPv6 version of the control buffer: http://lxr.free-electrons.com/source/net/ipv6/ip6_input.c?v=3.17#L219 If Netfilter modules are allowed to wash out control buffers, how does the IPv6 private data seems to be surviving the Netfilter chain? Thanks

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Question about switch_mm function
by Sreejith M M March 25, 2015

March 25, 2015

Hi, I was trying to understand the difference in scheduling between processes and threads(belong to same process). I was thinking that, when kernel has to switch to a task which belong to the same process, it does not have to clear / replace page global directories and other memory related information. But in switch_mm function some code is put under CONFIG_SMP function. What is its signigicance? Code is below(http://lxr.free-electrons.com/source/arch/x86/include/asm/mmu_context… . What I infer is that the code is doing flush tlb, reload page table directories etc in multiprocessor mode(obviously) but I believe this code may never be executed . Can anyone help to understand what this part of the function supposed to do? 60 #ifdef CONFIG_SMP 61 else { 62 this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK); 63 BUG_ON(this_cpu_read(cpu_tlbstate.active_mm) != next); 64 65 if (!cpumask_test_cpu(cpu, mm_cpumask(next))) { 66 /* 67 * On established mms, the mm_cpumask is only changed 68 * from irq context, from ptep_clear_flush() while in 69 * lazy tlb mode, and here. Irqs are blocked during 70 * schedule, protecting us from simultaneous changes. 71 */ 72 cpumask_set_cpu(cpu, mm_cpumask(next)); 73 /* 74 * We were in lazy tlb mode and leave_mm disabled 75 * tlb flush IPI delivery. We must reload CR3 76 * to make sure to use no freed page tables. 77 */ 78 load_cr3(next->pgd); 79 trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); 80 load_LDT_nolock(&next->context); 81 } 82 } 83 #endif -- Regards, Sreejith

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ACCESS_ONCE usage inside llist_add_batch function
by Cihangir Akturk March 4, 2015

March 4, 2015

Reading the lib/llist.c file in the kernel sources, I came across the llist_add_bach function defined like this; bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, struct llist_head *head) { struct llist_node *first; do { new_last->next = first = ACCESS_ONCE(head->first); } while (cmpxchg(&head->first, first, new_first) != first); return !first; } One thing bugging my mind is the ACCESS_ONCE macro. Is it really needed here ? I mean I would write this function with ACCES_ONCE moved outside the loop like as follows; bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, struct llist_head *head) { struct llist_node *first, *old; old = ACCESS_ONCE(head->first); for (;;) { first = old; new_last->next = old; old = cmpxchg(&head->first, first, new_first); if (old == first) break; } return !first; } I think that it may be faster to just use the return value of cmpxchg. But I am not sure about this. Is my understanding correct ?

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Beginner in Kernel Development
by sahil aggarwal March 3, 2015

March 3, 2015

Hi all, I am using linux since past 9-10 months and have good programming skills in C/C++. Since past few weeks i am looking for good source to dive in kernel development but could not find the starting point and proper order of learning to be followed to join the community. I will be grateful if someone could point me in right direction. Thanks Regards Sahil

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Re: Broadcom-sta (aka wl) --> Error! Bad return status for module build on kernel
by Andrey Skvortsov Feb. 28, 2015

Feb. 28, 2015

On 28 Feb, Lukas Singer wrote: > On Sat, Feb 28, 2015 at 06:19:20PM +0300, Andrey Skvortsov wrote: > > On 28 Feb, Lukas Singer wrote: > > > Hi Kernelnewbies, > > > > > > i am doing the eudytpula challenge, currently on task #2. > > > it is about building your own kernel and booting it. > > > > > > i successfully build the kernel and i am able to boot it but i have issues with my wlan driver. > > > > > > when i run `$ sudo make install´ i get this error: > > > Error! Bad return status for module build on kernel: 4.0.0-rc1-eudyptula-20150228+ (x86_64) > > > Consult /var/lib/dkms/broadcom-sta/5.100.82.112/build/make.log for more information. > > > > > > > > > i am on a debian system. lenovo edge e-135 notebook. > > > my current kernel comes from the official debian stable packages: > > > ~/linux/linux $ uname -r > > > 3.2.0-4-amd64 > > > > > > this is my wlan device: > > > ~/linux/linux $ lspci -nn | grep Network > > > 02:00.0 Network controller [0280]: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller [14e4:4727] (rev 01) > > > > > > i cannot go without wlan. > > > can anybody help? > > > > > > thanks in advance, > > > > > > lukas > > > > Hi, Lukas. > > > > Have you tried brcmsmac in-kernel driver? > > I am not sure about support status for BCM4313, but > > drivers/net/wireless/brcm80211/brcmsmac have a lot of code related t BCM4313. > > I have BCM4312 and am using successfully in-kernel driver instead of Broadcom's out-of-tree driver. > > > > Hi Andrey, > > i tried it again, it works perferctly! thanks. > i also tried the brcmsmac driver from the debian repositories under my > old 3.2 kernel and there it still was slow as hell, seems that the > wireless guys did a very good job improving this driver! > Congrats. That is another reason to run latest kernel. -- Best regards, Andrey Skvortsov Secure e-mail with gnupg: See http://www.gnupg.org/ PGP Key ID: 0x57A3AEAD

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Broadcom-sta (aka wl) --> Error! Bad return status for module build on kernel
by Lukas Singer Feb. 28, 2015

Feb. 28, 2015

Hi Kernelnewbies, i am doing the eudytpula challenge, currently on task #2. it is about building your own kernel and booting it. i successfully build the kernel and i am able to boot it but i have issues with my wlan driver. when i run `$ sudo make install´ i get this error: Error! Bad return status for module build on kernel: 4.0.0-rc1-eudyptula-20150228+ (x86_64) Consult /var/lib/dkms/broadcom-sta/5.100.82.112/build/make.log for more information. the make.log says: ... CFG80211 API is prefered for this kernel version Makefile:80: Neither CFG80211 nor Wireless Extension is enabled in kernel ... but i have cfg80211 configured! ~/linux/linux $ cat .config | grep "CFG80211" CONFIG_CFG80211=y # CONFIG_CFG80211_DEVELOPER_WARNINGS is not set # CONFIG_CFG80211_REG_DEBUG is not set CONFIG_CFG80211_DEFAULT_PS=y # CONFIG_CFG80211_DEBUGFS is not set # CONFIG_CFG80211_INTERNAL_REGDB is not set CONFIG_CFG80211_WEXT=y and i have wext configured! ~/linux/linux $ cat .config | grep "WEXT" CONFIG_WEXT_CORE=y CONFIG_WEXT_PROC=y CONFIG_WEXT_SPY=y CONFIG_WEXT_PRIV=y CONFIG_CFG80211_WEXT=y although the kernel installs and boots, but wlan doesn't work. i am on a debian system. lenovo edge e-135 notebook. my current kernel comes from the official debian stable packages: ~/linux/linux $ uname -r 3.2.0-4-amd64 this is my wlan device: ~/linux/linux $ lspci -nn | grep Network 02:00.0 Network controller [0280]: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller [14e4:4727] (rev 01) i cannot go without wlan. can anybody help? thanks in advance, lukas

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Re: Getting error "failed to setup attributes" on Adding Custom Fields in accelerometer HID driver
by s.rawat Feb. 27, 2015

Feb. 27, 2015

Do I need to define the all the Usage Tags in the input report of a sensor to retrieve minimum any one field or Only a Usage Tag which I wanted to retrieve is enough. e.g for an input report of an accelerometer which has the below fields(added new one in Bold), HID_USAGE_SENSOR_ACCEL_X_AXIS HID_USAGE_SENSOR_ACCEL_Y_AXIS HID_USAGE_SENSOR_ACCEL_Z_AXIS *HID_USAGE_SENSOR_DATA_MOTION_STATE,* *HID_USAGE_SENSOR_DATA_CUSTOM_VALUE_2* *HID_USAGE_SENSOR_DATA_CUSTOM_VALUE_3* *HID_USAGE_SENSOR_DATA_CUSTOM_VALUE_4* I want to retrieve Custom_Value_4 do I also need to define parameters for Data_Motion_state, Custom_Value2,Custom_Value3 as well apart from Custom_Value4 in the below structure. enum accel_3d_channel {.. } struct accel_3d_state {.. } static const struct iio_chan_spec accel_3d_channels[] = { ..} I did so but was getting error - "failed to setup attributes" but after I modified the code in the function : accel_3d_parse_report() like below to accommodate all the non Contigous Usage Tags and associated them with their channels - *_SCAN_INDEX_* . I did not get this error but some other error (listed at the end of the mail) //First Three channel X,Y and Z whose Usage Tags are contionus - 0x200453/54/55 for (i = 0; i <= CHANNEL_SCAN_INDEX_Z; ++i) { ret = sensor_hub_input_get_attribute_info(hsdev, HID_INPUT_REPORT, usage_id, HID_USAGE_SENSOR_ACCEL_X_AXIS + i, &st->accel[CHANNEL_SCAN_INDEX_X + i]); accel_3d_adjust_channel_bit_mask(channels, CHANNEL_SCAN_INDEX_X + i, st->accel[CHANNEL_SCAN_INDEX_X + i].size); } //Fourth channel For Data Motion - 0x200451 ret = sensor_hub_input_get_attribute_info(hsdev, HID_INPUT_REPORT, usage_id, HID_USAGE_SENSOR_DATA_MOTION_STATE, // For CHANNEL_SCAN_DATA_MOTION &st->accel[CHANNEL_SCAN_INDEX_X + i]); accel_3d_adjust_channel_bit_mask(channels, CHANNEL_SCAN_INDEX_X + i, st->accel[CHANNEL_SCAN_INDEX_X + i].size); //Last Three Channel for Custom Value 2,3,4 - 0x200545/46/47 for (i = 0; i <= 2; ++i) { ret = sensor_hub_input_get_attribute_info(hsdev, HID_INPUT_REPORT, usage_id, HID_USAGE_SENSOR_DATA_CUSTOM_VALUE_2 + i, &st->accel[CHANNEL_SCAN_INDEX_X + i + 4]); //start after CHANNEL_SCAN_DATA_MOTION Channel accel_3d_adjust_channel_bit_mask(channels, CHANNEL_SCAN_INDEX_X + i + 4, st->accel[CHANNEL_SCAN_INDEX_X + i].size); } But now I am getting a different error : [13778.127716] iio iio:device4: tried to double register : in_accel_x_index [13778.127899] hid_sensor_accel_3d HID-SENSOR-200073.3.auto: failed to initialize trigger buffer [13778.143676] hid_sensor_accel_3d: probe of HID-SENSOR-200073.3.auto failed with error -16 I am still figuring out where else Do I have to modify the code in order to receive the above custom values .. Thanks, S On Thu, Feb 26, 2015 at 6:54 PM, Daniel Baluta <daniel.baluta(a)gmail.com> wrote: > + linux-iio list. > > On Thu, Feb 26, 2015 at 8:04 AM, s.rawat <imsaurabhrawat(a)gmail.com> wrote: > > I have modified the hid-sensor-accel_3d.c driver to add the custom > fields - > > CHANNEL_SCAN_DATA_MOTION and HID_USAGE_SENSOR_DATA_CUSTOM_VALUEX ( X = > > 2,3,4). > > Below are my modifications : > > > > enum accel_3d_channel { > > CHANNEL_SCAN_INDEX_X, > > CHANNEL_SCAN_INDEX_Y, > > CHANNEL_SCAN_INDEX_Z, > > CHANNEL_SCAN_DATA_MOTION, > > CHANNEL_CUSTOM_VALUE_2, > > CHANNEL_CUSTOM_VALUE_3, > > CHANNEL_CUSTOM_VALUE_4, > > ACCEL_3D_CHANNEL_MAX, > > > > static const u32 accel_3d_addresses[ACCEL_3D_CHANNEL_MAX] = { > > HID_USAGE_SENSOR_ACCEL_X_AXIS, > > HID_USAGE_SENSOR_ACCEL_Y_AXIS, > > HID_USAGE_SENSOR_ACCEL_Z_AXIS, > > HID_USAGE_SENSOR_DATA_MOTION_STATE, > > HID_USAGE_SENSOR_DATA_CUSTOM_VALUE2, > > HID_USAGE_SENSOR_DATA_CUSTOM_VALUE3, > > HID_USAGE_SENSOR_DATA_CUSTOM_VALUE4 > > }; > > > > > > > > /* Channel definitions */ > > static const struct iio_chan_spec accel_3d_channels[] = { > > { > > .. > > .. > > .. > > { > > .type = IIO_ACCEL, > > .modified = 1, > > .channel2 = IIO_MOD_X, > > .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), > > .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) | > > BIT(IIO_CHAN_INFO_SCALE) | > > BIT(IIO_CHAN_INFO_SAMP_FREQ) | > > BIT(IIO_CHAN_INFO_HYSTERESIS), > > .scan_index = CHANNEL_SCAN_DATA_MOTION, > > }, > > { > > .type = IIO_ACCEL, > > .modified = 1, > > .channel2 = IIO_MOD_X, > > .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), > > .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) | > > BIT(IIO_CHAN_INFO_SCALE) | > > BIT(IIO_CHAN_INFO_SAMP_FREQ) | > > BIT(IIO_CHAN_INFO_HYSTERESIS), > > .scan_index = CHANNEL_CUSTOM_VALUE_2, > > }, > > { > > .type = IIO_ACCEL, > > .modified = 1, > > .channel2 = IIO_MOD_X, > > .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), > > .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) | > > BIT(IIO_CHAN_INFO_SCALE) | > > BIT(IIO_CHAN_INFO_SAMP_FREQ) | > > BIT(IIO_CHAN_INFO_HYSTERESIS), > > .scan_index = CHANNEL_CUSTOM_VALUE_3, > > }, > > { > > .type = IIO_ACCEL, > > .modified = 1, > > .channel2 = IIO_MOD_X, > > .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), > > .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) | > > BIT(IIO_CHAN_INFO_SCALE) | > > BIT(IIO_CHAN_INFO_SAMP_FREQ) | > > BIT(IIO_CHAN_INFO_HYSTERESIS), > > .scan_index = CHANNEL_CUSTOM_VALUE_4, > > } > > > > > > > > /* Capture samples in local storage */ > > static int accel_3d_capture_sample(struct hid_sensor_hub_device *hsdev, > > unsigned usage_id, > > size_t raw_len, char *raw_data, > > void *priv) > > { > > struct iio_dev *indio_dev = platform_get_drvdata(priv); > > struct accel_3d_state *accel_state = iio_priv(indio_dev); > > int offset; > > int ret = -EINVAL; > > > > switch (usage_id) { > > case HID_USAGE_SENSOR_ACCEL_X_AXIS: > > case HID_USAGE_SENSOR_ACCEL_Y_AXIS: > > case HID_USAGE_SENSOR_ACCEL_Z_AXIS: > > case HID_USAGE_SENSOR_DATA_MOTION_STATE: > > case HID_USAGE_SENSOR_DATA_CUSTOM_VALUE2: > > case HID_USAGE_SENSOR_DATA_CUSTOM_VALUE3: > > case HID_USAGE_SENSOR_DATA_CUSTOM_VALUE4: > > offset = usage_id - HID_USAGE_SENSOR_ACCEL_X_AXIS; > > > > > > > > /* Parse report which is specific to an usage id*/ > > static int accel_3d_parse_report(struct platform_device *pdev, > > struct hid_sensor_hub_device *hsdev, > > struct iio_chan_spec *channels, > > unsigned usage_id, > > struct accel_3d_state *st) > > { > > int ret; > > int i; > > > > for (i = 0; i <= CHANNEL_CUSTOM_VALUE_4; ++i) { //previously < > > CHANNEL_SCAN_INDEX_Z > > ret = sensor_hub_input_get_attribute_info(hsdev, > > > > > > > > After build /insmod i get the following dmesg : > > > > hid_sensor_accel_3d:HID-SENSOR-200073.3 auto : failed to setup attributes > > hid_sensor_accel_3d:HID-SENSOR-200073.3 auto.failed with error -1 > > > > > > I am not getting what else I have to modify to avoid this error .If i > remove > > the portion in bold(and use this original code > > : > http://lxr.free-electrons.com/source/drivers/iio/accel/hid-sensor-accel-3d.c > ) > > I can happily insert the module without any error and can interact with > the > > driver using my application. > > > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > >

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