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Questions about the zoned page frame allocator and fix mapped addresses
by Sunny Shah April 1, 2015

April 1, 2015

Hello, I have few more questions from my reading of "Understanding the Linux Kernel", chapter "Memory Management". - The book says, about releasing page frames to the per CPU cache - "no page frame is ever released to the cold cache: the kernel always assumes the freed page frame is hot with respect to the hardware cache". What is the reason for this decision ? - It is possible for a page to be in ZONE_NORMAL and yet have it's PG_reserved flag cleared. Is this correct ? - The function "fix_to_virt" for fix-mapped linear addresses does the following: return (0xfffff000UL - (idx << PAGE_SHIFT)); Why are the upper 4096 bytes not used, and the addressing starts from the top of the virtual address space - 4096 ? - The book says "each fix-mapped linear address maps one page frame of the physical memory". Shouldn't it be "maps one *physical location* of memory" rather than one page frame ? - My understanding is that the kernel page table entries for addresses > 896 MB would be empty and those addresses would be mapped using separate data structures used for temporary and permanent kernel mappings and non-contiguous page frame allocation. Is this wrong ? Thanks, Sunny

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what is the precise udev event that handles miscdevices?
by Robert P. J. Day April 1, 2015

April 1, 2015

i can trivially create misc character devices, and i know special device files for them will automatically show up under /dev, but what is the precise udev event/rule that comes into play for this? if i start to monitor udevadm with: $ udevadm monitor --kernel --udev --property and insert my misc char module, i see: KERNEL[5342.740294] add /module/mymisc (module) ACTION=add DEVPATH=/module/mymisc SEQNUM=3007 SUBSYSTEM=module KERNEL[5342.740528] add /devices/virtual/misc/mymisc (misc) ACTION=add DEVNAME=/dev/mymisc DEVPATH=/devices/virtual/misc/mymisc MAJOR=10 MINOR=55 SEQNUM=3008 SUBSYSTEM=misc UDEV [5342.741071] add /module/mymisc (module) ACTION=add DEVPATH=/module/mymisc SEQNUM=3007 SUBSYSTEM=module USEC_INITIALIZED=740419 UDEV [5342.741921] add /devices/virtual/misc/mymisc (misc) ACTION=add DEVNAME=/dev/mymisc DEVPATH=/devices/virtual/misc/mymisc MAJOR=10 MINOR=55 SEQNUM=3008 SUBSYSTEM=misc USEC_INITIALIZED=740750 so, yes, i can see the line "DEVNAME=/dev/mymisc", but is there something i can point at in the collection of udev rules that deals with that? or is that simply done internally? 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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coming shortly: series of simple kernel questions i should know the answers to
by Robert P. J. Day April 1, 2015

April 1, 2015

the lead-in: for the purposes of updating a pile of my existing kernel tutorials and courseware (and writing new material), i'm digging into the source to document numerous concepts from beginning to end, and i'm not surprised when i trip over all sorts of things that are fairly simple but i don't immediately know the answer to. so for the next while, i'm going to ask all sorts of questions to clarify numerous things, then i'll write up the final results and post them for public consumption at my web site so other people can take advantage of this. and i figured it would be useful to ask those questions on this list, as this list is full of clever people who probably know the answers. a lot of the early questions will be based on clarifying details of the driver model, as the current documentation under Documentation/driver-model/ is somewhat out of date so i desperately need to put together something far more current. first question(s) coming shortly ... 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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mmap text file
by Ssagarr Patil April 1, 2015

April 1, 2015

Hi, I am trying to achieve faster file writes using mmap. so I am trying the follwowing: /* open file */ while (loop) { /* get the current file size of output file */ filesize = lseek(outfd, 0, SEEK_END); /* Increase file size */ ftruncate(outfd, (off_t)filesize + (off_t)buf.size); /* mmap destination file */ if((dest = mmap(0, buf.size, PROT_WRITE, MAP_SHARED, outfd, filesize)) == (void *) -1) { printf( "Error mapping ouput file: %s: %d, %d\n", argv[1], i, filesize); perror("MMAP Failed\n"); goto error; } memcpy(dest, src, size); munmap(dest); } I am able to only mmap it once next time it fails to mmap, any pointers why it fails ? Regards, --Sagar

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The Eudyptula Challenge - Sending task
by Leonardo Ariel Carreras Rodríguez March 31, 2015

March 31, 2015

Hello everyone, I am trying to send Task 1. I already verified that my files do what they are supposed to. I am using mutt to send emails, so I have some questions. 1. Because gmail gives an advice about not using less secure apps, I am using another email address. Does Little care about the email or the ID is enough? 2. I attached as text using mutt the files that were required, but I am not sure if that is ok. An email was sent to Little from that 'new' account (not the one from which I started the challenge). 3. How long does it take to know if the task was completed, or at least that is waiting for correction? Regards, Leonardo Carreras

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How to auto-load kernel module when peripheral
by Woody Wu March 31, 2015

March 31, 2015

Hi, I want my usb-serial converter can be automatically ready to use after it plugged into an USB port. Currently I have to manually do 'modprobe ftdi_sio' before use it, otherwise, no module will be loaded and there is no a /dev/ttyUSB0 appearing. I am using mdev instead of udev in this embedded system, and full pathname of mdev had already put in /proc/sys/kernel/hotplug file. I also already added a line into my mdev.conf: ttyUSB* root:tty 660 To make it clear, the problem is when I inserted the convert, I did not see /dev/ttyUSB0 was created and 'lsmod' also not list the 'ftdi_sio' module. If I check the kernel message at the time of inserting the device, I can see: [ 43.425000] usb 1-1: new full speed USB device number 2 using s3c2416-ohci [ 43.585000] usb 1-1: New USB device found, idVendor=0403, idProduct=6001 [ 43.585000] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 43.585000] usb 1-1: Product: FT232R USB UART [ 43.585000] usb 1-1: Manufacturer: FTDI [ 43.585000] usb 1-1: SerialNumber: A900aMbV How do I do? Thanks in advance! -- Life is the only flaw in an otherwise perfect nonexistence -- Schopenhauer woody public key at http://subkeys.pgp.net:11371 (narkewoody(a)gmail.com)

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Re: Can add new module without upgrade the kernel?
by Woody Wu March 31, 2015

March 31, 2015

Sorry, I did not write a subject. On Monday, 30 March 2015, Woody Wu <narkewoody(a)gmail.com> wrote: > Hi, > > I have a kernel already run on production, but I then realized that I need > to add one or two driver to it. But I hope I can avoid to upgrade the > kernel image for those already running products, I hope I can only extend > the kernel by add the driver modules to the root file system. Is that > possible? The current kernel has already compiled with the loadable modules > options, but for the drivers that I want now the old config is 'no'. > > Thanks in advance. > -woody > > > -- > Sent from Gmail Mobile > -- Sent from Gmail Mobile

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(no subject)
by Woody Wu March 30, 2015

March 30, 2015

Hi, I have a kernel already run on production, but I then realized that I need to add one or two driver to it. But I hope I can avoid to upgrade the kernel image for those already running products, I hope I can only extend the kernel by add the driver modules to the root file system. Is that possible? The current kernel has already compiled with the loadable modules options, but for the drivers that I want now the old config is 'no'. Thanks in advance. -woody -- Sent from Gmail Mobile

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Sysfs requirement for running generic_buffer.c application - IIO sensors
by s.rawat March 30, 2015

March 30, 2015

I have two system having different kernel version and drivers(IIO) on which i can run the generic_buffer.c application .On one system it works fine but on the other it does not give the input reports data. I have checked that the system on which it is working has the following sysfs under /sys/bus/iio/devices/iio:deviceX (where X is 1,2,3...) buffer dev in_accel_hysteresis in_accel_offset in_accel_sampling_frequency in_accel_scale *in_accel_x_raw* *in_accel_y_raw* *in_accel_z_raw* name power scan_elements subsystem trigger uevent This is for accelerometer similiarly for magnetometer (in_magn_x_raw,_y_raw,z_raw etc) and for Gyrometer ( in_anglvel_x_raw,in_anglvel_y_raw,in_anglvel_z_raw ) and the one on which it is not working has the below sysfs under /sys/bus/iio/devices/iio:deviceX (where X is 1,2,3...) : buffer dev in_accel_hysteresis in_accel_offset in_accel_sampling_frequency in_accel_scale name power scan_elements subsystem trigger uevent Is the missing _x_raw,_y_raw and _z_raw component main reason for not working of the app,.Where I can enable them in the driver? Thanks and Rgds, Saurabh

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Time stamp of Kernel log prints is not including the suspend time
by manty kuma March 30, 2015

March 30, 2015

When CPU entered into power collapse, the time in the kernel log prints is not counting further. I mean to say that the time stamps of all the prints(end stage prints) during the power collapse are same and after resuming from power collapse, the time is continuing from here. The duration of suspend is not added to the kernel log's time stamps. I would like to know 1. So basically can I consider the wakeup time of the system until a particular print in kernel log is equal to its time stamp? 2. I would like to see in code how these time stamps are generated? Like, before going into power collapse, does it pause a timer or something? Best Regards, Manty

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