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Is there any good literature explaining Linux's file system ?
by Yubin Ruan July 10, 2016

July 10, 2016

Hi everybody, I'm really curious about whether there is any literature that describe Linux's file systems(e.g. ext2{3,4}, btrfs) deeply? I can't find much literature about Linux's filesystem. I have read some papers about Unix's file system. For example, **A Fast File System for UNIX**, which explain things in detail(though not so informative for me). I also read **Design and Implementation of the Second Extend Filesystem** by Remy, Theodore, et al. But those papers and blogs can't make thing clear for me, because there are so many things that they have not explained. I wonder is there any book that explain one of the Linux filesystem(design, implementation) in detail, like what Mal Gorman explain about Linux Memory Management in his books **Understand The Linux Memory Manager** and **Code Commentary On The Linux Virtual Memory Manager** ? Thanks in advance, Ruan.

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Re: Setting inode during lookup
by Bruce D. Wilner July 8, 2016

July 8, 2016

<petkov <at> uni-muenster.de> writes: > > On Tuesday 31 August 2004 20:00, Shehjar Tikoo wrote: > > Hi all. > Hi there, > > > > I have a query regarding lookups in VFS.Im using > > version 2.6.7. > > > > open_namei calls path_lookup, in case of a plain open, > > which in turn calls __emul_lookup_dentry, > > if the path is an absolute path. > > In __emul_lookup_dentry theres a call to path_walk > > which calls link_path_walk, Funny how they call this forum .*newbies. You wanna talk newbies, look at the Linux kernel code. Something as simple as namei() had to be split nito umpteen pieces, each of which is less organized than the next. The comments appear to have been written by children and are peppered with "in joke"-style wisecracks that only point to their authors' immaturity and lack of technical seniority. NEVER have I seen more disorganized code. Funny, the CAPTCHA word to enter was "exhumed." This sad sack replacement for namei() looks like it was exhumed from God-knows-where.

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CMA failure
by Ronit Halder July 8, 2016

July 8, 2016

Hi, I am going through CMA (Contiguous Memory Allocator) code. In, What situation CMA unable to allocate memory from a CMA area? regards, Ronit

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spi can't read more than 64 bytes
by Moti Cohen July 7, 2016

July 7, 2016

Hi all, I'm trying to write a kernel device driver for a Freescale imx6 processor based board. This driver is using spi to communicate with a radio module (using linux spi.c). I managed to wr/rd from the module, however once I'm trying to read more than 64 bytes I'm getting coruppted data. here are some details: The SPI reading process goes as follows: 1. Interrupt function is invoked from SPI device via dedicated GPIO line. 2. The interrupt function performs asynchronous SPI read in the following order: 2.1 radio_trx_end_callback is called, as it is the registered call back function. 2.2 radio_trx_end_callback calls hal_frame_read function which prepares spi_message and spi_transfer structures and fill them with relevant data: spi_device , data tx, transfer len , complete handler , … 3. The read itself is done by calling to function spi_async 4. The completion handler function is called and prints the read message, but trying to read more than 64 bytes in one transaction causes the read data to be corrupted. Any idea why am I seeing this behavior ? Is there (in Linux) any definition for the size to be read via the SPI ? The relevant variables and functions can be seen below: Thanks in advance for helping.. __________________________ uint8_t rx_buf[200]; uint8_t reg[200] = {HAL_TRX_CMD_FR, 0xff, 0xff}; struct spi_transfer transfer; struct spi_message spi_msg; // interrupt function //----------------------------------------------------------------------------------------------------------------------- static irq_handler_t radio_trx_end_callback(unsigned int irq, void *dev_id, struct pt_regs *regs) { hal_frame_read(irq, dev_id); return (irq_handler_t) IRQ_HANDLED; // Announce that the IRQ has been handled correctly } //read function //----------------------------------------------------------------------------------------------------------------------- void hal_frame_read(unsigned int irq, void *dev_id) { int status; spi_device->irq = irq; spi_message_init(&spi_msg); spi_msg.spi = spi_device; spi_msg.complete = rf_rx_completion_handler; spi_msg.context = NULL; memset((uint8_t*)&transfer, 0, sizeof(transfer)); memset(rx_buf, 0xFF, sizeof(rx_buf)); memset(reg, 0xFF, sizeof(reg)); reg[0] = HAL_TRX_CMD_FR; transfer.tx_buf = reg; transfer.len =64; transfer.rx_buf = rx_buf; spi_message_add_tail(&transfer, &spi_msg); memset(rx_buf, 0x0, sizeof(rx_buf)); status = spi_async(spi_device, &spi_msg); return; } //read completion handler //----------------------------------------------------------------------------------------------------------------------- static void rf_rx_completion_handler(void *arg) { int ii; //print the received message printk("\npure message: rx_buf [1]-2=%02X\n ", rx_buf [1]-2); for (ii=0; ii< rx_buf [1]-2; ii++) printk("%02X ", rx_buf [2+ii]); printk("\nframe len=%X actual len=%X status=%i\n",spi_msg.frame_length, spi_msg.actual_length, spi_msg.status); send_up_rf_event_to_workque(TRX_END_EVENT); }

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DMA address
by Ronit Halder July 7, 2016

July 7, 2016

Hi, What is a stale DMA address? I have another query. At the time of kernel crash, what happens to the iommu and what happens when devices try to DMA onto memory? regards, Ronit

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memblock structure
by Ronit Halder July 7, 2016

July 7, 2016

There are three memblock_type members memory , reserved and physmem in memblock structure. What is the significance of each member? regards, Ronit

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Developing Linux Kernel Driver for media Codec Driver
by Hao Zhang July 7, 2016

July 7, 2016

hi all i am developing a linux kernel driver for a 4-CH AHD2.0 RX and 9-CH Audio Codec which is named nvp6124 . wedsite : http://www.nextchip.com/ch/products/product.asp?hGubun=AHD. below are few of its characteristics: video codec: it digitizes and decodes ntsc/pal/comet/AHD1.0/AHD2.O video signal into digital video components which represents 8bit bt656/1120 4:2:2 byte interleave fotmat. audio codec: output pcm digital signal converted from analog audio input signals and analog audio signals converted from pcm digital audio. control interface: control and configure through i2c interface. video interface: 4ch analog video input and output 2ch digital signal, each channal has 8 data ports and a clk clock port which can connect to the embedded processer. audio interface(two i2s interface): audio data convert to PCM data,and outputed via i2s interface . PCM data can also input via i2s interface, the input audio data is outputed via internal DAC. i want to submit the driver, but i have some problem on the below points: 1.must i submit the driver through device tree binding? Does the kernel tree accept the driver without device tree binding? just see the video interface ,i know i2c port can binding below the i2c node, but, how can i bind other data port and clock signal port with device trees? 2.how to use device tree to bind device and how does the kernel uses it to match device? can i obtain some document about this? 3.i creat the driver for Cubieboard one(allwinner a10 processer) and Banana PI BPI-M1(allwinner a20 processer) ,if i submit patch ,which kernel version shoudle i use ? must i use the lastest kernel (download in www.kernel.org isn't the sdk of the board)in that boards ? 4.does someone know which lastest kernel version does Cubieboard one and Banana PI BPI-M1 supports? 5.the maintainer doesn't has the device, how do they know the driver is work well on my board? just buit without error or warning ? Best regards :) Hao Zhang

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what is the minimal version of make supported for building the kernel?
by Robert P. J. Day July 6, 2016

July 6, 2016

another curiosity related to my current travels through the initramfs code, i noticed this git commit from back in 2013: $ git show 7ac1815683 commit 7ac181568342ec618d4da1ab03c2babcaa7ee84f Author: Jan Beulich <JBeulich(a)suse.com> Date: Wed Dec 18 17:08:57 2013 -0800 fix build with make 3.80 According to Documentation/Changes, make 3.80 is still being supported for building the kernel, hence make files must not make (unconditional) use of features introduced only in newer versions. Commit 1bf49dd4be0b ("./Makefile: export initial ramdisk compression config option") however introduced "else ifeq" constructs which make 3.80 doesn't understand. Replace the logic there with more conventional (in the kernel build infrastructure) list constructs (except that the list here is intentionally limited to exactly one element). Signed-off-by: Jan Beulich <jbeulich(a)suse.com> Cc: P J P <ppandit(a)redhat.com> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org> diff --git a/Makefile b/Makefile index 858a147..89cee86 100644 --- a/Makefile +++ b/Makefile @@ -732,19 +732,13 @@ export mod_strip_cmd # Select initial ramdisk compression format, default is gzip(1). # This shall be used by the dracut(8) tool while creating an initramfs image. # -INITRD_COMPRESS=gzip -ifeq ($(CONFIG_RD_BZIP2), y) - INITRD_COMPRESS=bzip2 -else ifeq ($(CONFIG_RD_LZMA), y) - INITRD_COMPRESS=lzma -else ifeq ($(CONFIG_RD_XZ), y) - INITRD_COMPRESS=xz -else ifeq ($(CONFIG_RD_LZO), y) - INITRD_COMPRESS=lzo -else ifeq ($(CONFIG_RD_LZ4), y) - INITRD_COMPRESS=lz4 -endif -export INITRD_COMPRESS +INITRD_COMPRESS-y := gzip +INITRD_COMPRESS-$(CONFIG_RD_BZIP2) := bzip2 +INITRD_COMPRESS-$(CONFIG_RD_LZMA) := lzma +INITRD_COMPRESS-$(CONFIG_RD_XZ) := xz +INITRD_COMPRESS-$(CONFIG_RD_LZO) := lzo +INITRD_COMPRESS-$(CONFIG_RD_LZ4) := lz4 +export INITRD_COMPRESS := $(INITRD_COMPRESS-y) ... etc etc ... now, Documentation/Changes currently does indeed state: Current Minimal Requirements ============================ ... snip ... o GNU make 3.80 # make --version but i did a quick grep to find: $ grep -r "else ifeq" * lib/raid6/test/Makefile:else ifeq ($(HAS_NEON),yes) $ so would that single test not violate the rule just described above? is Documentation/Changes entirely up to date with respect to minimal requirements? 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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Re: Bios , Mbr, Grub
by Gnoleba GNOGBO July 6, 2016

July 6, 2016

Hi ! Thanks for your answears. Can you give le the link where i can find "Understanding the linux system startup " please ? Regards Gnoleba Le 6 juil. 2016 04:00, "arshad hussain" <arshad.super(a)gmail.com> a écrit : > > > On 04-Jul-2016, at 2:30 pm, Gnoleba GNOGBO <gnognoleba(a)gmail.com> wrote: > > > > Hi ! > > > > I had read a lot of book and link about initialization of the boot > starting of linux. > > > > I read that , after the post by the bios the mbr is loaded in memory > which routine load this sector ? > > This is architecture specific and is done by BIOS. > > > In this sector of 512 bytes we have 440 bytes for a routine what is the > function of this routine ? > > Actually its 446 bytes. These are executable code. > > 16bytes per partition * 4 = 64bytes + (0xAA55) 2 bytes for MBR Marker = > 66bytes > > 512 - 66 = 446 bytes > > > When this routine is executed ? > > Just after POST. Done by BIOS. > > > The 2 bytes with 0xAA55 what is its function ? > > Its denotes that the sector is executable. Can also be seen as Marker. > > > Who load it in memory ? And the all book i had read said the mbr load > the loader grub How ? And the grub launch the kernel, ok . How this grub is > load ? By which programm ? > > So, i would like that someone give me the names of routines, the order > of their launching and which load or execute what until the grub exécution ? > > I would suggest work it floppy on qemu/bochs first to understand then > gradually > move on to partition tables and boot loaders. > > Read “Understanding the linux kernel” - System Startup chapter for > thorough understanding. > > Thanks. > > > > > Thank you for your help. > > Greg i am waiting a lot from you ! > > > > Best regards > > Gnoleba GNOGBO > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >

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memblock structure
by Ronit Halder July 5, 2016

July 5, 2016

There are three memblock_type members memory , reserved and physmem in memblock structure. What is the significance of each member? regards, Ronit

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