July 2018 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Question about memcpy
by bing zhu July 17, 2018

July 17, 2018

Dear Sir/Ma'am Thank you for your time ,i'm a student new to linux kernel. I have a question about memcpy,i noticed that memcpy is faster in kernel than in user space for example : in a module helloworld , i use memcpy to copy a 4096B to a block of memory for like 10000 times and in user space i do the same thing,I noticed that kernel is faster than user , is it possible that in kernel when i insmod hello it can not be scheduled but in user space it will so kernel is faster? is there a possible way that a user task can run a block of code that uninterruptable? No switch ,no schedule ? Thank you !

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Re: newly add MAP_SYNC flag to mmap
by Alex Arvelaez July 17, 2018

July 17, 2018

16.07.2018 10:15 PM David Frank <david_frank95(a)yahoo.com> napisał(a): > > Thanks Valdis. > > Yes, I got the kernel and header files installed. > > But there seems to be a lot of mman.h. I found one in /usr/include/asm-generic that defined MAP_SYNC, and I included it also, now I got passed compile and linking. I feel like your toolchain should be able to pick up the right file when you do #include <sys/mman.h> Regards, Alex

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Trying to export per process network bandwidth stats under /proc/[pid]/
by Amos Bird July 14, 2018

July 14, 2018

Hello! I'm trying to add a proc entry under /proc/[pid] in order to get per process network bandwidth stats. I suppose it's similar to /proc/[pid]/io . However I couldn't find a modular way to add entries under /proc/[pid]. This thread https://lists.kernelnewbies.org/pipermail/kernelnewbies/2011-January/000475… suggests modifying the kernel which isn't practical to me. Here is what I've found by going through a bit of the related kernel code. 1. I need to find a way to override or hooking `sock_sendmsg`/`sock_recvmsg` functions with accounting variables like `task_io_accounting` 2. a way to add proc entries under /proc/[pid] with readops printing `current` netio accounting variables. Am I on the right path of implementing this? Thanks! -- Amos Bird amosbird(a)gmail.com

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mmap huge page and MAP_SYNC flag support
by David Frank July 12, 2018

July 12, 2018

Hi,How do I enable the MAP_SYNC flag in mmap for linux 4.15, my code does not compile with that flag on linux 4.15.0-041500rc7-generic #201801072330 Also, how do I make mmap support map size of 2GB or larger, currently the call to mmap fails with mapsize of 2GB. thanks, David

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What does the "-DPACKAGE" means?
by Dengke Du July 12, 2018

July 12, 2018

Hi all What does the "-DPACKAGE" means? ``````````````````````````````````````````````````````````` $(OUTPUT)test-libbfd.bin: $(BUILD) -DPACKAGE='"perf"' -lbfd -lz -liberty -ldl ``````````````````````````````````````````````````````````` In this link: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/tools/buil…

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Use of enums, why?
by John Whitmore July 11, 2018

July 11, 2018

I only learning the ropes, and might have missed the memo on the use of enums so forgive me. I have looked at https://www.kernel.org/doc/html/v4.10/process/coding-style.html#macros-enum… but that didn't answer my question. I'm doing a clean up of staging:rtl8192u: clearing out checkpatch errors and triming out data structures which aren't used in the code. So I came across a typedef of an enumerated type in the file: drivers/staging/rtl8192u/r8192U.h typedef enum rf_optype { RF_OP_By_SW_3wire = 0, RF_OP_By_FW, RF_OP_MAX } rf_op_type; A quick grep for this type in drivers/staging/rtl8192u directory shows that the type is never used outside that header definition. So I can remove it? Well no you can't because the values defined in the enum are used. In drivers/staging/rtl8192u/r8192U_core.c for example: priv->Rf_Mode = RF_OP_By_SW_3wire; that element priv->Rf_Mode is defined in the structure typedef struct r8192_priv { ... u8 Rf_Mode; /* For Firmware RF -R/W switch */ ... } So now to the question, as I understand it the compiler will use an int type for the enumerated type. The data structure r8192_priv doesn't use this int type because the programmer knows that a u8 will do to hold the 3 possible values defined by the enumerated type. So you're saving a few bytes in a data structure, which I'm happy about, but the point of enumerated types is, as I understand it, so that the compiler can do some checking to ensure a value is not assigned in error. Since the enum isn't being used, there is no compiler type checking, so why use an enumerated type? Might as well have used three #define values. The obvious thing to do is leave well enough alone. But I had to ask what is the correct implementation? Use the enum in the data structure, instead of u8? Or just #define a few constants? #define RF_OP_By_SW_3wire 1 #define RF_OP_By_FW 2 #define RF_OP_MAX 3 Given the space saving of u8 over int I'd probably go with the #define. Guess it depends on how many of those data structures are being declared. thanks for any thoughts or clarification John

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[linux-3.12.19] - kernel panic observed
by Sriram July 10, 2018

July 10, 2018

Hi, I m working on linux-3.12.19 kernel. In our board, we have an IPsec tunnel which carries IPv6 traffic inside Packet structure looks like below, IPv4(OuterIP) || ESP || IPv6(Inner IP) || IPv6 Frag HDR || UDP || Payload. I have written an application which constructs Inner IPv6 packets and writes to raw socket. Through application I m generating IPv6 packets of length not more than 1340. If length of the IPv6 packet is more than 1340, application does the IPv6 fragmentation and 2 fragments are written to raw socket. If I run this application using a script continously, there is no issue observed for around 30-40 mins. After that we see kernel panic with the stack trace like below. Unable to handle kernel paging request for data at address 0x000004d0 Faulting instruction address: 0xc000000000789578 Oops: Kernel access of bad area, sig: 11 [#1] SMP NR_CPUS=24 CoreNet Generic Modules linked in: shm(O) l1d(O) hetmgr(O) sl_reset(O) cu_led(O) airv1588(O) CPU: 7 PID: 2512 Comm: pdcpUlSockTh Tainted: G W O 3.12.19-rt30 #1 task: c0000003fb42dc40 ti: c0000003ef9a0000 task.ti: c0000003ef9a0000 NIP: c000000000789578 LR: c00000000078ca48 CTR: c00000000078c8f0 REGS: c0000003ef9a2f10 TRAP: 0300 Tainted: G W O (3.12.19-rt30) MSR: 0000000080029000 <CE,EE,ME> CR: 24008422 XER: 20000000 SOFTE: 1 DEAR: 00000000000004d0, ESR: 0000000000000100 GPR00: c00000000078ca48 c0000003ef9a3190 c000000000d6b3a0 c0000003ef9a33a0 GPR04: 0000000000000000 c0000003ef9a3740 000000000000000a c0000003ef9f1c80 GPR08: c0000003ef9f1c80 00000000000004d0 0000000000000001 000000007abc6dbb GPR12: 0000019f1a2654f8 c00000000fff7480 00000000107ce2ec 000000001075fc10 GPR16: 0000000000000011 c000000000d56200 0000000000000000 000000001d8a2000 GPR20: 0000000000000000 0000000000000040 c000000000e74b48 c0000003ef9a3200 GPR24: c000000000cbc480 c0000003ef9a3740 c0000003ef9a33a0 c0000003ef9a3740 GPR28: 000000000000000a c000000074b86000 c0000003ef9f1c80 000000000000000a NIP [c000000000789578] .xfrm_resolve_and_create_bundle+0x78/0xbb4 LR [c00000000078ca48] .xfrm_bundle_lookup+0x158/0x6f8 Call Trace: [c0000003ef9a3190] [c0000003ef9a32c0] 0xc0000003ef9a32c0 (unreliable) [c0000003ef9a3330] [c00000000078ca48] .xfrm_bundle_lookup+0x158/0x6f8 [c0000003ef9a3400] [c0000000006d1a9c] .flow_cache_lookup+0x43c/0x4f4 [c0000003ef9a34e0] [c00000000078d348] .xfrm_lookup+0x260/0x6a4 [c0000003ef9a3610] [c0000000007a7edc] .ip6_dst_lookup_flow+0x8c/0xc0 [c0000003ef9a36b0] [c0000000007ca3d0] .rawv6_sendmsg+0x264/0xcc8 [c0000003ef9a3820] [c000000000758c18] .inet_sendmsg+0x98/0x110 [c0000003ef9a38c0] [c000000000694124] .sock_sendmsg+0x94/0xf4 [c0000003ef9a3a20] [c000000000694738] .___sys_sendmsg+0x340/0x350 [c0000003ef9a3c20] [c0000000006990c8] .__sys_sendmsg+0x58/0xb4 [c0000003ef9a3d00] [c0000000006dac94] .compat_sys_sendmsg+0x48/0x70 [c0000003ef9a3d90] [c0000000006db228] .compat_sys_socketcall+0x2b4/0x310 [c0000003ef9a3e30] [c0000000000005a4] syscall_exit+0x0/0x8c Instruction dump: fbc1fff0 fbe1fff8 f821fe61 7c7a1b78 7cdf3378 7c942378 7cb92b78 7cfe3b78 60000000 60000000 e93a0000 3ae10070 <e9290000> 7f43d378 7e84a378 7f25cb78 Kindly let me know if there is any patch available to fix this issue. If further details are required, I can post. Regards, Sriram

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Question about watchdog
by bing zhu July 10, 2018

July 10, 2018

Dear Sir/Ma'am Thank you for your time ,i'm a student new to linux kernel.at present ,i'd like to create a kernel thread say use kthread_create func ,my question is :how can i make this thread to run on a cpu and never get switched or scheduled , there is a while(1).....structure in that thread i need it to do work . at present i comes with errors like "NMI watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [test thread :1881]",i understand there is a watchdog but is there anyway i can feed the dog myself and let my thread have cpu as much as i want ? thanks again ,any information would be great ! best wishes!

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Re: [PATCH] vsprintf: fix build warning
by Tobin C. Harding July 10, 2018

July 10, 2018

CC'ing kernel newbies for anyone else trying to learn how linux-next works. On Fri, Jul 06, 2018 at 11:49:51AM -0400, Steven Rostedt wrote: > On Fri, 6 Jul 2018 23:42:13 +0900 > Sergey Senozhatsky <sergey.senozhatsky(a)gmail.com> wrote: > > > On (07/06/18 15:47), Arnd Bergmann wrote: > > [..] > > > Fixes: bfe80ed3d7c7 ("vsprintf: add command line option debug_boot_weak_hash") > > > > Seems like this one is still in linux-next. > > Can we squash this patch and bfe80ed3d7c7? > > > > I prefer not to do squashes unless absolutely necessary. Yes, it is in > next, but even branches pulled into next should try to resist rebasing > (I never rebase my next branch unless there is a real bug that will > break bisecting). Steve if you do not rebase your next branch and the branch ends up containing fixes to patches like the above doesn't this mean that when you do a pull request to Linus the branch you are asking to be pulled will be too 'dirty' i.e. I thought that the pull request should be like a patch set and only contain the 'final product' not every change that was made during development? I was under the impression that each maintainer constantly rebased their next branches and that was why one has to checkout the tagged linux-next each day instead of just pulling. From information on the net somewhere I have been checking out linux-next using this shell function checkout-next () { local branch='linux-next' git checkout master git remote update linux-next git branch -D $branch git checkout -b $branch $(git tag -l "next-*" | tail -1) } Also, when my leaks tree got included in linux-next I was told that it was ok to rebase and have since been rebasing mercilessly. thanks in advance for your time, Tobin.

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Regarding Signing Linux kernel with Microsoft secure boot keys for UEFI
by inventsekar July 8, 2018

July 8, 2018

Sorry, added the subject .. On Fri 6 Jul, 2018, 11:22 AM inventsekar, <inventsekar(a)gmail.com> wrote: > Dear All,.... > > so I was reading on Quora.... > > https://www.quora.com/What-are-some-features-that-Linus-Torvalds-dismissed-… > > Signing Linux kernel with Microsoft secure boot keys for UEFI. That was > suggested by RedHat developers and Linus flipped them off in his > character... > I went to that link and read two three times, but I could not understand. > > > Could you explain this above issue, on a newbies perspective. > > > Best regards, sekar >

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