June 2015 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

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

4 8

How to handle float-point operations
by 慕冬亮 July 9, 2015

July 9, 2015

I know there are rarely float-point operations! What's the exception? In the linux kernel, how does it handle the float-point operations in the userland? - mudongliang

5 7

[PATCH 0/4] staging: wilc1000: cover letter
by Luis de Bethencourt July 7, 2015

July 7, 2015

Patches to be applied on top of https://patchwork.kernel.org/patch/6655831/ Thanks! Luis

2 2

Changel anguage
by Gnoleba GNOGBO July 4, 2015

July 4, 2015

Hi ! I would like to change my language to french please. Best regards Gnoleba

2 2

Linux's MMC driver and SDCard life time doubt
by Daniel. July 2, 2015

July 2, 2015

Hi for all, I have an application running on top of an sd card formated with vfat. This application is Java and uses ActiveMQ on same vfat sdcard filesystem, the ActiveMQ generates a huge I/O on sdcard. I know that SDCards sectors have an specific writing limits. I want to know if Linux's mmc driver would spare the writes across whole SDCard improving its life time or if this role is to be played by filesystem? The SDCards live about 15 days before crashing, after crashing I can't format it again, I have no idea about tools for getting a status of SD remaing life time, any pointing would be helpful! Thanks in advance! -- *"Do or do not. There is no try"* *Yoda Master*

2 1

working with linux-next ... must tags be fetched separately?
by Robert P. J. Day July 1, 2015

July 1, 2015

perusing the current instructions on how to work with linux-next here: https://www.kernel.org/doc/man-pages/linux-next.html and i'm puzzled by this part of the instructions: Fetch linux-next plus tags $ git fetch linux-next ... $ git fetch --tags linux-next ... is it really necessary to run two separate fetch commands? from the man page for git-fetch, one reads: -t, --tags Fetch all tags from the remote (i.e., fetch remote tags refs/tags/* into local tags with the same name), in addition to whatever else would otherwise be fetched. so would it not be sufficient to run simply: $ git fetch --tags linux-next or am i misreading something? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

3 3

Divide Error: 0000 [#1] SMP
by Sioban July 1, 2015

July 1, 2015

Hello, I have a problem with my server, it's several times I got "Divide Error: 0000 [#1] SMP". I'm not qualified enough to identify the problem. This is the message, I got : ---------------------------------------------------------------------------------------------------------------------------- [1639377.680125] divide error: 0000 [#1] SMP [1639377.680149] Modules linked in: dm_mod lp parport_pc joydev st sr_mod cdrom xt_multiport nfnetlink_queue nfnetlink nf_conntrack_ipv4 nf_defrag_ipv4 xt_tcpudp iptable_filter ip_tables xt_iprange xt_conntrack nf_conntrack ipt_REJECT xt_mark xt_NFQUEUE x_tables binfmt_misc arc4 ecb md4 hmac nls_utf8 cifs dns_resolver fscache pl2303 usbserial ext4 crc16 mbcache jbd2 snd_hda_codec_hdmi nouveau mxm_wmi wmi video snd_hda_intel snd_hda_controller snd_hda_codec snd_hwdep snd_pcm ttm drm_kms_helper drm snd_timer i2c_algo_bit iTCO_wdt snd iTCO_vendor_support soundcore pcspkr evdev serio_raw kvm_intel kvm shpchp i2c_i801 i2c_core lpc_ich mfd_core asus_atk0110 button processor thermal_sys hwmon_vid coretemp loop fuse ppdev parport autofs4 xfs crc32c_generic libcrc32c hid_generic usbhid hid raid1 md_mod sg sd_mod [1639377.680439] crc_t10dif crct10dif_generic crct10dif_common ata_generic ahci libahci ata_piix pata_jmicron atl1 mii libata ehci_pci uhci_hcd ehci_hcd scsi_mod usbcore usb_common [last unloaded: parport_pc] [1639377.680513] CPU: 2 PID: 2618 Comm: pgld Not tainted 3.16.0-4-686-pae #1 Debian 3.16.7-ckt9-3~deb8u1 [1639377.680542] Hardware name: System manufacturer P5K/P5K, BIOS 1201 10/14/2008 [1639377.680571] task: f0855560 ti: efe54000 task.ti: efe54000 [1639377.680589] EIP: 0060:[<c125bfad>] EFLAGS: 00010246 CPU: 2 [1639377.680609] EIP is at div64_u64+0x2d/0x160 [1639377.680626] EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: 00000000 [1639377.680644] ESI: 00000000 EDI: 00000000 EBP: efe55d4c ESP: efe55d28 [1639377.680662] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 [1639377.680680] CR0: 80050033 CR2: b776b000 CR3: 2fd55000 CR4: 000007f0 [1639377.680698] Stack: [1639377.680711] 00000416 00000000 efe55d4c c111f6b6 0000ba44 00000000 00000000 0000005b [1639377.680749] 00000000 efe55d80 c111f97d 00000000 00000000 00000000 0000005b 00000000 [1639377.680788] 00010000 00000001 00000212 00000000 00000416 f0fb0ea0 efe55e18 c1120dce [1639377.680826] Call Trace: [1639377.680845] [<c111f6b6>] ? pos_ratio_polynom+0x36/0xa0 [1639377.680863] [<c111f97d>] ? bdi_position_ratio.isra.11+0x15d/0x200 [1639377.680883] [<c1120dce>] ? balance_dirty_pages_ratelimited+0x17e/0x690 [1639377.680903] [<c11985f2>] ? generic_write_end+0xb2/0xe0 [1639377.680932] [<f8073380>] ? xfs_vm_write_end+0x40/0xe0 [xfs] [1639377.680951] [<c11171a2>] ? generic_perform_write+0x132/0x1a0 [1639377.680981] [<f8080abb>] ? xfs_file_buffered_aio_write+0xfb/0x1a0 [xfs] [1639377.681011] [<f8080bc9>] ? xfs_file_write_iter+0x69/0x130 [xfs] [1639377.681031] [<c11706d9>] ? cp_new_stat64+0x109/0x120 [1639377.681049] [<c116c099>] ? new_sync_write+0x69/0xa0 [1639377.681067] [<c116c030>] ? do_iter_readv_writev+0x90/0x90 [1639377.681084] [<c116c53d>] ? vfs_write+0x9d/0x1d0 [1639377.681102] [<c116cc06>] ? SyS_write+0x46/0x90 [1639377.681120] [<c147bcdf>] ? sysenter_do_call+0x12/0x12 [1639377.681137] Code: e5 57 56 53 83 ec 18 89 44 24 10 8b 45 0c 89 54 24 14 85 c0 75 40 8b 4c 24 14 8b 5d 08 89 ce 39 cb 0f 87 17 01 00 00 89 c8 31 d2 <f7> f3 31 d2 89 c1 89 f0 f7 f3 89 d6 8b 5c 24 10 89 f2 89 cf 89 [1639377.681292] EIP: [<c125bfad>] div64_u64+0x2d/0x160 SS:ESP 0068:efe55d28 [1639377.681522] ---[ end trace 22f807c15589e633 ]--- ---------------------------------------------------------------------------------------------------------------------------- I also got this message on my SSH session: ---------------------------------------------------------------------------------------------------------------------------- Message from syslogd@shax <mailto:syslogd@shax> at Fri Jun 12 13:55:36 2015 ... shax vmunix: [1639377.681137] Code: e5 57 56 53 83 ec 18 89 44 24 10 8b 45 0c 89 54 24 14 85 c0 75 40 8b 4c 24 14 8b 5d 08 89 ce 39 cb 0f 87 17 01 00 00 89 c8 31 d2 <f7> f3 31 d2 89 c1 89 f0 f7 f3 89 d6 8b 5c 24 10 89 f2 89 cf 89 Message from syslogd@shax <mailto:syslogd@shax> at Fri Jun 12 13:55:36 2015 ... shax vmunix: [1639377.681292] EIP: [<c125bfad>] div64_u64+0x2d/0x160 SS:ESP 0068:efe55d28 ---------------------------------------------------------------------------------------------------------------------------- My system: ---------------------------------------------------------------------------------------------------------------------------- uname -a Linux shax 3.16.0-4-686-pae #1 SMP Debian 3.16.7-ckt9-3~deb8u1 (2015-04-24) i686 GNU/Linux ---------------------------------------------------------------------------------------------------------------------------- Have you any idea from where it can comes ? Or at least, tell where I should go to have some help (kernel.org ?)

6 12

How to get clk rate using clk name?
by victorascroft＠gmail.com June 26, 2015

June 26, 2015

Hello, I am writing a driver for a device which does not require a clock specified in the device tree and always has the clock enabled for it. In this driver I require the clock rate of a specific clock, let's say having the name "foo", for a specific timing calculation. Having this clock name, is it possible to get the clock rate?. With functions like clk_get_rate it is mandatory to have the struct clk pointer to the specific clock which I do not have. While it is definitely possible to specify a clock explicitly in the DT specification and then have the clock allocation done in the clock driver for the SoC, since the peripheral block does not require the clock explicitly, I did like to avoid this. Is this doable? Something like clk_lookup_by_name("foo") returning a struct clk pointer. Regards.

1 0

Filesize in sysfs, debugfs, ...
by Stephan Müller June 26, 2015

June 26, 2015

Hi all, I have a question, what is the policy on file size in sysfs and especially in debugfs? Many (but not all) of the files report a size of 0. Recently I diffed against a file in sysfs. The files were identical, despite the fact one reported size 0. I got the unpleasant result diff -as file1 file2 (treat both as text, report identical files) Files file1 and file2 are identical diff -asq file1 file2 (treat both as text, report just yes/no) Files file1 and file2 differ In brief mode diff looks first for file sizes and stops if they don't match. For files which don't differ in size (e.q, exposing a bool) it would be easy to set the proper size for others it's not. Thank you, Stephan

1 0