April 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

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Documentation for usbmouse.c
by Ronit Halder May 9, 2015

May 9, 2015

Where do i get documentation for usb mouse ( usbmouse.c ).I was reading /home/roni/linux/drivers/hid/usbhid/usbmouse,c and i am unable to understand some part of it.So,i need help.

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About bootmem allocation/freeing flow
by yoma sophian May 5, 2015

May 5, 2015

hi all: I have several questions about free_all_bootmem_core: 1. In __free_pages_bootmem, we set set_page_count(p, 0) while looping nr_pages, why we need to set_page_refcounted(page) before calling __free_pages? 2. how about the pages that allocated by calling alloc_bootmem_xxxx? in free_all_bootmem, we just free the pages that used to record bootmem stage present pages like below. if so, isn't possible the pages got by calling alloc_bootmem_xxxx will be over-written by later page allocation ? page = virt_to_page(bdata->node_bootmem_map); pages = bdata->node_low_pfn - bdata->node_min_pfn; pages = bootmem_bootmap_pages(pages); count += pages; while (pages--) __free_pages_bootmem(page++, 0); appreciate your kind help in advance,

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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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Re:execve error
by Avinash Sridharan April 30, 2015

April 30, 2015

Are you passing the arguments to execve correctly? Usually the EFAULT error occurs, cause the argument format to execve is not correct and the kernel is unable to interpret the executable that needs to be launched, or the parameters that need to be passed to the new process. Just an example: http://www.linuxquestions.org/questions/programming-9/execve-alwayse-produc… On Thu, Apr 23, 2015 at 9:00 AM <kernelnewbies-request(a)kernelnewbies.org> wrote: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. How can I fetch the files likely directory > /usr/src/kernels/<kernel version> from kernel source tree? > (tianlilai) > 2. execve error (Rohith) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 23 Apr 2015 17:59:56 +0800 > From: tianlilai <laitianli2015(a)outlook.com> > Subject: How can I fetch the files likely directory > /usr/src/kernels/<kernel version> from kernel source tree? > To: kernelnewbies(a)kernelnewbies.org > Message-ID: <BLU436-SMTP88F0913B3897AE70E7C950A9ED0(a)phx.gbl> > Content-Type: text/plain; charset="utf-8"; format=flowed > > > Hi,I have built the kernel source tree and running in PC mechine.Now I > want to fetch the files likely directory /usr/src/kernels/<kernel > version> from this kernel source tree.How can I do? Thanks very much! > > > > > ------------------------------ > > Message: 2 > Date: Thu, 23 Apr 2015 17:55:22 +0530 > From: Rohith <itsnotrohit(a)gmail.com> > Subject: execve error > To: kernelnewbies(a)kernelnewbies.org > Message-ID: > < > CABsTBT6S0vRNFo0bxxBcWDx3k8JMpzbYyKbbUB8oxT-W%2B8Tr-A(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hi all, > > I'm facing a strange issue with execve. It fails with -EFAULT > intermittently. I found that whenever it failed the stack allocated to the > process is in the last page of the CONFIG_TASK_SIZE. > > For example, if CONFIG_TASK_SIZE is set to 0x4000_0000, the process would > fail in execve if the stack happens to be in the page: > > 3ffdf000-40000000 rw-p 00000000 00:00 0 [stack] > > I tried changing CONFIG_TASK_SIZE=0x30000000 and the process this time > fails at the end 0x30000000 address. > > I also found that the execve seem to use the largest stack address > (STACK_TOP_MAX, function __bprm_mm_init(), fs/exec.c) while copying > argv/envp to the new process space. > > I don't know how to debug further. I feel that the user process stack > should never be allocated at the CONFIG_TASK_SIZE? Any idea or suggestion > on how to debug further, please tell me. > > thanks, > rohit >

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[PATCH] .gitignore: Simplify Git ignoring generated directories.
by Robert P. J. Day April 29, 2015

April 29, 2015

Signed-off-by: Robert P. J. Day <rpjday(a)crashcourse.ca> --- am i correct in assuming that this change, first of all, makes it clear that only directories are involved and, also, that one can simply ignore all directories with the name "generated"? diff --git a/.gitignore b/.gitignore index 4ad4a98..9301b0c 100644 --- a/.gitignore +++ b/.gitignore @@ -68,9 +68,8 @@ Module.symvers # # Generated include files # -include/config -include/generated -arch/*/include/generated +include/config/ +generated/ # stgit generated dirs patches-* 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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4.1-rc1 fails with O3 optimization
by Andev April 28, 2015

April 28, 2015

Hello Newbies, I usually compile my kernel with an unsupported O3 option(why not? :). Today after running the latest 4.1-rc1 kernel with O3, I got a boot failure. This is the first time this has happened for me. If someone is interested in debugging this, please read on. Can you try to reproduce this bug? If yes, can you also bisect this? I am a bit swamped right now and can try to reproduce this only on Wednesday. If you are interested, apply the following patch, compile and see if the kernel boots. Thanks! diff --git a/Makefile b/Makefile index 14c722f..05950ca 100644 --- a/Makefile +++ b/Makefile @@ -297,8 +297,8 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \ HOSTCC = gcc HOSTCXX = g++ -HOSTCFLAGS = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu89 -HOSTCXXFLAGS = -O2 +HOSTCFLAGS = -Wall -Wmissing-prototypes -Wstrict-prototypes -O3 -fomit-frame-pointer -std=gnu89 +HOSTCXXFLAGS = -O3 ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1) HOSTCFLAGS += -Wno-unused-value -Wno-unused-parameter \ @@ -616,7 +616,7 @@ KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os $(call cc-disable-warning,maybe-uninitialized,) else -KBUILD_CFLAGS += -O2 +KBUILD_CFLAGS += -O3 endif -- Andev

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Re: 4.1-rc1 fails with O3 optimization
by leo kirotawa April 28, 2015

April 28, 2015

that .config you sent is for 4.0-rc2, is that right? here is the diff after a make oldconfig [1] [1] http://pastebin.com/4Lfs2it0 On Tue, Apr 28, 2015 at 12:35 PM, Andev <debiandev(a)gmail.com> wrote: > On Tue, Apr 28, 2015 at 9:03 AM, leo kirotawa <kirotawa(a)gmail.com> wrote: >> I could boot it using qemu. So what's the point? > > Could you try the attached config and see if it boots? > >> >> On Tue, Apr 28, 2015 at 2:41 AM, Andev <debiandev(a)gmail.com> wrote: >>> >>> On Mon, Apr 27, 2015 at 9:00 PM, Bobby Powers <bobbypowers(a)gmail.com> >>> wrote: >>> > Hello, >>> > >>> > Andev wrote: >>> >> I usually compile my kernel with an unsupported O3 option(why not? :). >>> > >>> > Because there have been publications that show on major benchmarks, >>> > the effects of -O3 are indistinguishable from noise: >>> > http://people.cs.umass.edu/~emery/pubs/Stabilizer-UMass-CS-TR2011-43.pdf >>> > >>> > Have you noticed that -O3 provides any performance benefits over -O2? >>> > >>> >>> Look here: http://www.spinics.net/lists/kernel/msg1962561.html >>> >>> Btw, this will help uncover problems in either gcc or the kernel for >>> sure. So no harm in trying! >>> >>> -- >>> Andev >>> >>> _______________________________________________ >>> Kernelnewbies mailing list >>> Kernelnewbies(a)kernelnewbies.org >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >> >> >> >> -- >> >> ---------------------------------------------- >> Leônidas S. Barbosa (Kirotawa) >> blog: corecode.wordpress.com > > > > -- > Andev -- ---------------------------------------------- Leônidas S. Barbosa (Kirotawa) blog: corecode.wordpress.com

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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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