October 2015 - kernelnewbies@kernelnewbies.org

get all the file_system_type registered in linux kernel
by 慕冬亮 Oct. 24, 2015

Oct. 24, 2015

Recently I am learning vfs in kernel. I want to write a kernel module, which can show all the file_system_type registered in linux kernel. But the list head of all the file_system_type - file_systems can't be got through some API! So I check all the file systems in the /proc/filesystems. And use get_fs_type() and file system type name to get the corresponding file_system_type variable. Does someone has easy method to achieve my goal? And how do I read file in the proc file system, for example, /proc/filesystems? Thanks in advance. -mudongliang

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Block Device Settings
by Rishi Agrawal Oct. 24, 2015

Oct. 24, 2015

Hi, I have written a block device driver. I now want to set few limits on it so that it can perform efficiently. Kernel Version : 3.13.0-24-generic #46-Ubuntu SMP 1. I want to limit the number of bio's in one request to 1. 2. I want to limit the number of blocks in a bio to 1. 3. I want to change the block_size/sector_size of the device to 4K/8K/16K/32K based on the user's input. How can I achieve these settings? I found the following settings but I am not very much sure that these are the right ones. Also setting these parameters might end up having a adverse performance issue on the system, which I am not aware about. Please guide. File: blk-settings.c blk_queue_max_segments() blk_queue_max_segment_size() blk_queue_logical_block_size() blk_queue_physical_block_size() blk_limits_io_min() blk_queue_io_min() blk_limits_io_opt() -- Regards, Rishi Agrawal A simple act of caring creates an endless ripple. Be the change that you wish to see in the world. Be thoroughly used up when you die, for the harder you work, the more you live.

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Query Hard Memory Addresses
by Kenneth Adam Miller Oct. 22, 2015

Oct. 22, 2015

So, previously it was discussed that /dev/mem could be used to mmap a specific hardware memory into a process. Now I need to unit test some userland code that does exactly that, but I need to make sure that the unit test selects a small page that is always free in kernel land. How can I query mem to just grab the location of a free page? (my development setup is different from my other deployment; in deployment these values are hard coded, in development they occur on a qemu emulator)

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SHA-1 hash calculate in Kernel.
by lx Oct. 22, 2015

Oct. 22, 2015

hi all: I built a module for calculate the SHA-1. The code is: ################## #include <linux/init.h> #include <linux/module.h> #include <linux/kernel.h> #include <linux/crypto.h> #include <linux/err.h> #include <linux/scatterlist.h> MODULE_LICENSE("Dual BSD/GPL"); #define SHA1_LENGTH 20 static int hello_init(void) { /* * http://lxr.oss.org.cn/source/fs/ecryptfs/crypto.c?v=2.6.30 */ struct scatterlist sg; struct hash_desc desc; //way 1 /* char *plaintext = "c"; size_t len = strlen(plaintext); */ //way 2 /* char *plaintext = kmalloc(sizeof(char), GFP_KERNEL); plaintext = "c"; size_t len = 1; */ // way 3. /* char plaintext[1] = {'c'}; size_t len = 1; */ // way 4. /* char *plaintext = (char *)__get_free_page(GFP_KERNEL); memcpy(plaintext, "c", 1); size_t len = 1; */ int rc = 0; int i; char hashtext[SHA1_LENGTH]; memset(hashtext, 0x00, SHA1_LENGTH); printk(KERN_INFO "sha1: %s\n", __FUNCTION__); sg_init_one(&sg, plaintext, len); desc.tfm = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC); desc.flags = 0; rc = crypto_hash_init(&desc); if (rc) { printk(KERN_ERR "%s: Error initializing crypto hash; rc = [%d]\n", __func__, rc); goto out; } rc = crypto_hash_update(&desc, &sg, len); if (rc) { printk(KERN_ERR "%s: Error updating crypto hash; rc = [%d]\n", __func__, rc); goto out; } rc = crypto_hash_final(&desc, hashtext); if (rc) { printk(KERN_ERR "%s: Error finalizing crypto hash; rc = [%d]\n", __func__, rc); goto out; } crypto_free_hash(desc.tfm); for (i = 0; i < 20; i++) { printk(KERN_INFO "%02x-%d\n", hashtext[i]&0xff, i); } out: printk(KERN_INFO "end\n"); return rc; } static void hello_exit(void) { printk(KERN_ALERT "Goodbye, cruel world\n"); } module_init(hello_init); module_exit(hello_exit); ################## I can just get the right result by way 3 and 4, In way 1 and 2 , I get the wrong result, I check the result by link: http://www.xorbin.com/tools/sha1-hash-calculator . Please tell me why? Thank you.

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How to reserve physical address space region
by sahlot arvind Oct. 21, 2015

Oct. 21, 2015

Hi, Is there an API kernel exposes to use for a driver in order to reserve physical address space? I mean I want to reserve 5GB (or more if allowed) of contiguous physical address space anywhere in the address range (wherever it is available.. doesn't matter) and then I want to map that physical address range in the kernel to get a virtual address so that my driver can dereference that virtual pointer to access the mapped physical address range. Thanks in advance! Sahlot

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(no subject)
by Rock Lee Oct. 21, 2015

Oct. 21, 2015

unsubscribe kernelnewbies Regards ---- Rock Lee

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UIO Kernel Driver with Buildroot and QEMU
by Kenneth Adam Miller Oct. 21, 2015

Oct. 21, 2015

So I'm building a uio kernel driver with buildroot, and I've gotten the driver to compile, installed it and can insmod it in the final buildroot target after booting the image with QEMU. I'm on linux kernel version 3.14, and I followed the guide here: https://www.kernel.org/doc/htmldocs/uio-howto/userspace_driver.html And it describes the location on where the device file that should be opened by userland code as either one of two locations: /dev/uioX, with X being a number or /sys/class/uio/uioX But the each of following returns nothing: ls /dev/uio* ls /sys/class/uio/ After I compile the uio example that is provided in the linux source at source/drivers/uio/uio.c and uio_dmem_genirq.c, and insmod them, I do modprobe uio and modprobe uio_dmem_genirq and each of those return nothing. However, I do see that /sys/modules/uio and /sys/modules/uio_dmem_genirq What am I doing wrong? Or where are the respective device files that I'm supposed to use in my userland driver process? int fd = open("where is it!!?"); mmap(...., fd,..);

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Enable/disable cpu
by Doug Wilson Oct. 20, 2015

Oct. 20, 2015

All, I have been looking at sysfs cpu side code. Had a quick question. On my x86 box: #ls /sys/devices/system/cpu/ I see 4 cpus plus a few more fields such as online/present/possible etc. This come from drivers/base/cpu.c. My question here is, in each of those cpu0-3 folders, there's file by name online which one can use to disable/enable cpu using cpumask. Could someone point me to that code, I could not really pin point to where exactly this attribute is defined. Am just exploring cpu hotplug feature. Thanks.

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clk: Two-output clk provider with standard clk consumer
by Mason Oct. 19, 2015

Oct. 19, 2015

[ This was first sent to the linux-clk@vger ML, but it seems like they only deal with actual patches, not general noob-ish questions ] Hello everyone, I'm trying to write a clk driver. To summarize, the platform has a 27 MHz crystal feeding two PLLs (pll0 and pll1), each feeding resp. cpuclk and sysclk. On my first try, I wrote one DT node for each element, and life was good. But Stephen Boyd wrote: > More discussion will come with the binding, but we're pushing > people towards making real platform drivers for their clock > controllers, instead of parsing everything out of DT and having > one node per clock. So if these are picking things out of some > larger clock controller block, please rewrite the binding to be a > real clock provider. So... I've tried to write a clk driver with the following features: - a single input (crystal oscillator, modeled by fixed-clock) - two separate outputs (cpuclk and sysclk) derived from two separate internal PLLs (pll0 and pll1) I would like to use cpuclk as the input to a fixed-factor-clock node (cpuclk/2). So the device tree would look like this: clocks { ranges; #address-cells = <1>; #size-cells = <1>; xtal: xtal { compatible = "fixed-clock"; clock-frequency = <27000000>; #clock-cells = <0>; }; clkgen: clkgen@10000 { compatible = "foo,clkgen"; reg = <0x10000 0x30>; clocks = <&xtal>; #clock-cells = <1>; }; periphclk: periphclk { compatible = "fixed-factor-clock"; clocks = <&clkgen 0>; clock-mult = <1>; clock-div = <2>; #clock-cells = <0>; }; }; Does this look OK so far? The driver would look like this: (headers and error handling omitted for brevity) static struct clk *output[2]; static struct clk_onecell_data clk_data = { output, 2 }; static void __iomem *clkgen_base; static void __init make_pll(const char *name, const char *parent, void __iomem *reg) { struct clk *clk; unsigned int val, mul, div; val = readl_relaxed(reg); mul = foo(val); div = bar(val); clk = clk_register_fixed_factor(NULL, name, parent, 0, mul, div); printk("clk = %p\n", clk); } static void __init clkgen_setup(struct device_node *np) { int ret; const char *parent = of_clk_get_parent_name(np, 0); clkgen_base = of_iomap(np, 0); make_pll("pll0", parent, clkgen_base + 0); make_pll("pll1", parent, clkgen_base + 8); output[0] = clk_register_divider(NULL, "cpuclk", "pll0", 0, clkgen_base + 0x24, 8, 8, CLK_DIVIDER_ONE_BASED, NULL); output[1] = clk_register_fixed_factor(NULL, "sysclk", "pll1", 0, 1, 3); ret = of_clk_add_provider(np, of_clk_src_onecell_get, &clk_data); printk("ret=%d out0=%p out1=%p\n", ret, output[0], output[1]); } CLK_OF_DECLARE(myclkgen, "foo,clkgen", clkgen_setup); But the periphclk setup fails because the fixed-factor-clock driver only looks up the parent name using of_clk_get_parent_name ("clkgen" in my case) and calls: clk_register_fixed_factor(NULL, "periphclk", "clkgen", 0, 1, 2); Which doesn't keep track of the clkgen output index... <confused> Can someone please point out what I am missing? Thanks!

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System freezes with Kernel BUG at kernel/time/timer.c:1108 run_timer_softirq()
by Raghavendra. S Oct. 19, 2015

Oct. 19, 2015

Hi, In my x86 laptop I could observe random panic with Fatal exception in interrupt. We are testing Wi-Fi with our own driver issue occur randomly after 2-3 hours of testing. Panic is due to fatal except in interrupt and Kernel stack trace is run_timer_softirq()->__run_timers()->cascade()->BUG_ON(tbase_get_base(timer->base) != base); [image: Inline image 1] Any pointers to debug this will be of great help. -Raghu

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