July 2021 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

trigger timestamp
by Muni Sekhar July 8, 2021

July 8, 2021

Hi all, >From the user space test application , Is it possible to get the trigger timestamp corresponding to SNDRV_PCM_TRIGGER_START & SNDRV_PCM_TRIGGER_STOP events for audio playback capture? -- Thanks, Sekhar

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Re: How to comment or reply to others?
by Abd-Alrhman Masalkhi July 4, 2021

July 4, 2021

I am working at the moment by lieferando, and I newbies in the linux kernel development. I do it as hobby

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How to better control IMA module?
by Xiaolong Wang July 2, 2021

July 2, 2021

Hi all, I have a question regard to kernel IMA module. I’ve enabled IMA on one of my Linux server with `ima=on ima_policy=tcb` everything seems working fine. The only issue is that after about a week the `/sys/kernel/security/ima/ascii_runtime_measurements` grow out of control. As for now I have about 80K items in the file. I also have a customized attestation application that compares the runtime measurements with a list of known “good” measurements. this size of runtime measurements make it substantially long to run the attestation application. Is there a way to limit the size of the `/sys/kernel/security/ima/ascii_runtime_measurements` (not ideal, since some important info might get lost) Is there a way to clean the items in `/sys/kernel/security/ima/ascii_runtime_measurements` (also not ideal, for the same reason as above) Is there a way to control which file the kernel measures (e.g., I found lot of /tmp files are measured which are not necessary) Will the kernel running out of memory? Any suggestions will be deeply appreciated! Thank you -Daniel

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Seeking advice on "monkey patching" a driver
by Ian Pilcher July 2, 2021

July 2, 2021

I maintain a couple of out-of-tree modules that enable "mainstream" distributions to be used on the Thecus N5550 NAS. https://github.com/ipilcher/n5550/tree/master/modules The disk activity LEDs in this NAS are software controlled, so the n5550_ahci_leds module exists to "inject" a wrapper around libahci's qc_issue() function which triggers the correct LED (if any). https://github.com/ipilcher/n5550/blob/25538096fffd7942be8b7f2c66af580620a4… It's certainly a hack, but it makes use of the modules much simpler, as there's no need to patch and rebuild libahci, override the distro- provided module, etc. As long as modprobe is configured to load n5550_ahci_leds immediately after libahci and before any consumers of libahci are loaded, things "just work". The current version of n5550_ahci_leds attempts to ensure that no libahci consumers are loaded before it modifies libahci's ahci_ops.qc_issue. It does this by: * locking module_mutex * getting a reference to the libahci module (with find_module()) * checking libahci's reference count * grabbing a reference to *itself* to prevent itself from being unloaded * modifying ahci_ops.qc_issue * unlocking module_mutex (There similar logic in the n5550_ahci_leds_enabled_store function to reverse the modifications, if no other libahci consumers are loaded.) It's very possible that some or all of these precautions are unnecessary (or that they're inadequate). I am most definitely not an expert at kernel development or the details of the kernel's module loading mechanism. I and few others have, however, been successfully using these modules for a number of years. I've just discovered that neither module_mutex nor find_module() are available in recent kernels, and I'm unsure how to proceed. The two options that I've been able to think of thus far are: * YOLO! I can simply remove the checks from the module and rely on user space to ensure that n5550_ahci_leds is loaded before any libahci consumers load (i.e. before udevd starts). * kprobes - I have a feeling that this is the "correct" way to do this (and it would have the benefit of working even if libahci or its consumers aren't built as modules). OTOH, it isn't clear how I would go about accessing the arguments passed into the function without JProbes, and I'm not thrilled with the idea of adding additional overhead and/or locking to the disk I/O path. I'd really appreciate any thoughts, advice, ideas, links etc. Thanks! -- ======================================================================== In Soviet Russia, Google searches you! ========================================================================

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kernel build error during ubuntu linux kernel build
by ckim＠etri.re.kr July 1, 2021

July 1, 2021

Hello, all I have a strange problem in building the linux kernel from ubuntu. (I want to replace the kernel in ubuntu to debug install failure on qemu virtual machine) I downloaded ubuntu source by "git clone git://kernel.ubuntu.com/ubuntu/ubuntu-focal.git". and because I wanted to use a specific version, I did "git checkout Ubuntu-5.4.0-42.46" (this version is the one used in a ubuntu installation .iso. And you can see related askubuntu question here : https://askubuntu.com/questions/1347390/what-ubuntu-source-version-should-i- use-to-add-some-debug-prints-for-ubuntu-bo ) After git-checkout, the `git log` shows this result : commit 98c4545e2d65ed35c31056f72c4da20f6b5ea0d0 (HEAD, tag: Ubuntu-5.4.0-42.46) Author: Khalid Elmously <khalid.elmously(a)canonical.com> Date: Thu Jul 9 19:50:26 2020 -0400 UBUNTU: Ubuntu-5.4.0-42.46 Signed-off-by: Khalid Elmously <khalid.elmously(a)canonical.com> To build the kernel, I did `ARCH=arm64 CROSS_COMPILE=aarch64-none-elf- make defconfig` and `ARCH=arm64 CROSS_COMPILE=aarch64-none-elf- make -j24 Image`. But this gives me a compile error below. What can be wrong? . . CC mm/interval_tree.o CC drivers/base/regmap/regcache.o CC kernel/time/posix-cpu-timers.o CC mm/list_lru.o CC block/blk-mq.o AS arch/arm64/lib/memchr.o CC fs/ext4/migrate.o security/security.c: In function 'security_add_hooks': security/security.c:477:25: error: 'struct security_hook_heads' has no member named 'socket_getpeersec_stream' 477 | &security_hook_heads.socket_getpeersec_stream) | ^ CC kernel/time/posix-clock.o AS arch/arm64/lib/memcmp.o security/security.c: In function 'security_setprocattr': CC arch/arm64/kvm/../../../virt/kvm/arm/vgic/vgic-v2.o security/security.c:2058:27: error: 'union security_list_options' has no member named 'socket_getpeersec_stream' 2058 | socket_getpeersec_stream.socket_getpeersec_stream = NULL; | ^ In file included from ./include/linux/timer.h:5, from ./include/linux/workqueue.h:9, from ./include/linux/bpf.h:9, from security/security.c:13: security/security.c:2060:25: error: 'struct security_hook_heads' has no member named 'socket_getpeersec_stream' 2060 | &security_hook_heads.socket_getpeersec_stream, | ^ ./include/linux/list.h:857:12: note: in definition of macro 'hlist_entry_safe' 857 | ({ typeof(ptr) ____ptr = (ptr); \ | ^~~ security/security.c:2059:3: note: in expansion of macro 'hlist_for_each_entry' 2059 | hlist_for_each_entry(hp, | ^~~~~~~~~~~~~~~~~~~~ security/security.c:2060:25: error: 'struct security_hook_heads' has no member named 'socket_getpeersec_stream' 2060 | &security_hook_heads.socket_getpeersec_stream, | ^ ./include/linux/list.h:857:28: note: in definition of macro 'hlist_entry_safe' 857 | ({ typeof(ptr) ____ptr = (ptr); \ | ^~~ security/security.c:2059:3: note: in expansion of macro 'hlist_for_each_entry' 2059 | hlist_for_each_entry(hp, | ^~~~~~~~~~~~~~~~~~~~ In file included from ./include/linux/list.h:9, from ./include/linux/timer.h:5, from ./include/linux/workqueue.h:9, from ./include/linux/bpf.h:9, from security/security.c:13: ./include/linux/kernel.h:993:17: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast] 993 | void *__mptr = (void *)(ptr); \ | ^ ./include/linux/list.h:847:40: note: in expansion of macro 'container_of' 847 | #define hlist_entry(ptr, type, member) container_of(ptr,type,member) | ^~~~~~~~~~~~ . . BTW, when I do the same with linux-5.4.21 vanila source, it compiles ok. Can anyone give me an advice? Could this Ubuntu-5.4.0-42.46 version have a bug and maybe I need a patch? Thank you! Chan Kim

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