February 2012 - kernelnewbies@kernelnewbies.org

some questions about log level
by loody June 29, 2012

June 29, 2012

hi all: my questions are below: 1. Can I temporarily let kernel message show in stdout? I google some key word as "console_loglevel" and I found following methods: a. echo 8 > /proc/sys/kernel/printk b. write a simple program which calling "klogctl(8, NULL, level)" Then I purposely connect/disconnect USB, but my console keep quiet. But dmesg shows connect/disconnect messages. 2. what is differences between above a and b methods? Are they not to used to change console_loglevel? 3. is it possible the max level of "console_loglevel" doesn't mean it will show on stdout? -- Thanks for your help

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Need help: Generating patch using git
by amit mehta March 8, 2012

March 8, 2012

Hi, kernel janitors group seem like a good place to start learning linux kernel and after reading some of the information available on kernel newbies website, i tried to generate a dummy patch and need your help for moving in correct direction of learning and contributing to linux kernel. So these are the steps that i've followed to generate this dummy patch. 1: Download the latest linux kernel sources using git # mkdir linux-next # cd linux-next # git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git linux-2.6 2: Do some modifications. # pwd /root/linux-next/linux-2.6 # git diff diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c index 6e412a6..9858701 100644 --- a/net/ipv4/ipconfig.c +++ b/net/ipv4/ipconfig.c @@ -441,7 +441,7 @@ static int __init ic_defaults(void) &ic_myaddr); return -1; } - printk("IP-Config: Guessing netmask %pI4\n", &ic_netmask); + printk(KERN_INFO "IP-Config: Guessing netmask %pI4\n", &ic_netmask); } return 0; 3: Generate a patch # pwd /root/linux-next/linux-2.6 # mkdir ../patches # git diff >../patches/ipconfigPatch.txt 4: Test your patch 4a: Clear the local changes from the tree # git checkout -f 4b: Apply the patch # git apply ../patches/ipconfigPatch.txt The above step(4b) did not returned any git error so it seems to me that the steps to generate this patch was correct. 5: Check your mailer 5a: I just copied the contents of ../patches/ipconfigPatch.txt and pasted in the compose area and sent that mail to myself. After receiving this mail i copied and pasted the mail contents in a file under /root/linux-next/patches/dummyPatch.txt and tried to apply this patch using git but it gave me an error as below: # git apply ../patches/dummy.txt fatal: corrupt patch at line 11 Hence it seems i'm missing something here. Please note that this is just for my understanding purpose of generating and submitting patches. -Amit

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error in git clone
by Mayank Agarwal Feb. 28, 2012

Feb. 28, 2012

Hi all, I am trying to create the git repository of linux kernel but on doing git clone i am getting the following error: sudo git clone git:// git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git Initialized empty Git repository in /home/mayank/linuxkernel/linux-stable/.git/ ^[[Agit.kernel.org[0: 149.20.4.72]: errno=Connection timed out fatal: unable to connect a socket (Connection timed out) I tried disabling firewall also but that is also of not help. Any reasons why this error is happening and how can i get over this. Thanks and Regards, Mayank

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How to debug system freeze?
by Łukasz Sowa Feb. 28, 2012

Feb. 28, 2012

Hi, I'm experiencing strange bug when I close lid of my laptop - system freezes (no reaction on keys, no response form ssh) hard and displays some strange colour effects. The kernel log (after reboot) shows nothing. My question is - how to debug it? Maybe there's a way to track last called kernel function or something similar? Thanks, Lukasz Sowa

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mask out an irq line
by cheneydeng Feb. 28, 2012

Feb. 28, 2012

hi all, I know that when an interrupt handler is excuting, the irq line which generated the signal will be masked out,however,if the line is shared by many device.Will all be masked out or just the one which is handling now be masked out ?Doed it tell the difference by the forth argument of request_irq() ? ------------------ best regards！ cheneydeng

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Re: USB Scanner driver
by Manavendra Nath Manav Feb. 28, 2012

Feb. 28, 2012

Hi Oliver, On Tue, Feb 28, 2012 at 2:12 PM, Oliver Neukum <oneukum(a)suse.de> wrote: > Am Dienstag, 28. Februar 2012, 09:32:13 schrieb Manavendra Nath Manav: >> Hi All, >> >> I have connected Metrologic USB Scanner, but Fedora is not able to attach a >> driver to it. Is there a generic USB scanner driver which I can associate > > Apart from a few very old scanners which are repackaged SCSI devices, > scanners are handled by libusb. There is no kernel driver involved. > >> with it to make it work? This scanner is HID compliant device. Can't I make >> usbhid driver to make the scanner work? The sources from Metrologic said >> that it should work in USB Keyboard emulation mode. How to enable this? > > Keyboard emulation is a bad idea. You need to find the correct backend of SANE > for your scanner. > > Regards > Oliver In my Barcode scanner device SANE utility is not supported according to the documentation of Metrologic. Is it correct that SANE is predominately used for image capture functionality? how we can use it for barcode scanning? -- Manavendra Nath Manav

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Re: USB Scanner driver
by Manavendra Nath Manav Feb. 28, 2012

Feb. 28, 2012

Hi Ondrez >>>Hi All, >>> >>>I have connected Metrologic USB Scanner, but Fedora is not able to attach a >>>driver to it. Is there a generic USB scanner driver which I can associate >>>with it to make it work? This scanner is HID compliant device. Can't I make >>>usbhid driver to make the scanner work? The sources from Metrologic said >>>that it should work in USB Keyboard emulation mode. How to enable this? >>> >>><<< dmesg snip >>> >>>[ 7002.199153] usb 8-2: new low speed USB device using uhci_hcd and address >>>18 >>>[ 7002.373938] usb 8-2: New USB device found, idVendor=0c2e, idProduct=0200 >>>[ 7002.373943] usb 8-2: New USB device strings: Mfr=1, Product=2, >>>SerialNumber=0 >>>[ 7002.373946] usb 8-2: Product: Honeywell Scanning and Mobility Scanner >>>[ 7002.373949] usb 8-2: Manufacturer: Honeywell Scanning and Mobility >>>[ 7002.399070] input: Honeywell Scanning and Mobility Honeywell Scanning and >>>Mobility Scanner as >>>/devices/pci0000:00/0000:00:1d.2/usb8/8-2/8-2:1.0/input/input13 >>>[ 7002.399170] generic-usb 0003:0C2E:0200.000B: input,hidraw2: USB HID v1.11 >>>Keyboard [Honeywell Scanning and Mobility Honeywell Scanning and Mobility >>>Scanner] on usb-0000:00:1d.2-2/input0 >>>[ 7008.463407] usb 8-2: USB disconnect, address 18 >>>[ 7011.780271] usb 8-2: new low speed USB device using uhci_hcd and address >>>19 >>>[ 7011.957957] usb 8-2: New USB device found, idVendor=0c2e, idProduct=0720 >>>[ 7011.957962] usb 8-2: New USB device strings: Mfr=1, Product=2, >>>SerialNumber=0 >>>[ 7011.957965] usb 8-2: Product: Honeywell Scanning and Mobility Scanner >>>[ 7011.957968] usb 8-2: Manufacturer: Honeywell Scanning and Mobility >>>[root@pe1800xs ~]# cat /proc/bus/usb/devices >>>T: Bus=08 Lev=01 Prnt=01 Port=01 Cnt=01 Dev#= 19 Spd=1.5 MxCh= 0 >>>D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 >>>P: Vendor=0c2e ProdID=0720 Rev= 1.00 >>>S: Manufacturer=Honeywell Scanning and Mobility >>>S: Product=Honeywell Scanning and Mobility Scanner >>>C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=450mA >>>I:* If#= 0 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=00 Prot=00 Driver=(none) >>>E: Ad=02(O) Atr=03(Int.) MxPS= 8 Ivl=10ms >>>E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=10ms >>>-- >>>Thanks & Regards, >>>Manavendra Nath Manav On Tue, Feb 28, 2012 at 2:15 PM, Ondrej Zary <linux(a)rainbow-software.org> wrote: > On Tuesday 28 February 2012, Manavendra Nath Manav wrote: >> Hi All, >> >> I have connected Metrologic USB Scanner, but Fedora is not able to attach a >> driver to it. Is there a generic USB scanner driver which I can associate >> with it to make it work? This scanner is HID compliant device. Can't I make >> usbhid driver to make the scanner work? The sources from Metrologic said >> that it should work in USB Keyboard emulation mode. How to enable this? > > You forgot to say that this is a *barcode* scanner. It should work fine in USB > keyboard mode. If it's configured in some other mode, use the "MetroSelect > Configuration Guide" to change the mode (by scanning some special barcodes). > > > -- > Ondrej Zary Yeah, I forgot to mention that it's a barcode scanner. I reconfigured the device mode as USB HID keyboard as given in the Metrologic manual. Now the driver associated with it shows as "usbhid". But still when i scan any barcode i am not able to see any output on the console. Is there any redirection required? -- Manavendra Nath Manav

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Semaphore
by SaNtosh kuLkarni Feb. 28, 2012

Feb. 28, 2012

A certain kernel process has acquired a semaphore lock and meanwhile during this period the process gets killed abruptly (and it has not released the sem lock..//.sem down).....and the other processes cannot acquire the lock, what can be done in this case. -- *Regards, Santosh Kulkarni*

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USB Scanner driver
by Manavendra Nath Manav Feb. 28, 2012

Feb. 28, 2012

Hi All, I have connected Metrologic USB Scanner, but Fedora is not able to attach a driver to it. Is there a generic USB scanner driver which I can associate with it to make it work? This scanner is HID compliant device. Can't I make usbhid driver to make the scanner work? The sources from Metrologic said that it should work in USB Keyboard emulation mode. How to enable this? <<< dmesg snip >>> [ 7002.199153] usb 8-2: new low speed USB device using uhci_hcd and address 18 [ 7002.373938] usb 8-2: New USB device found, idVendor=0c2e, idProduct=0200 [ 7002.373943] usb 8-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [ 7002.373946] usb 8-2: Product: Honeywell Scanning and Mobility Scanner [ 7002.373949] usb 8-2: Manufacturer: Honeywell Scanning and Mobility [ 7002.399070] input: Honeywell Scanning and Mobility Honeywell Scanning and Mobility Scanner as /devices/pci0000:00/0000:00:1d.2/usb8/8-2/8-2:1.0/input/input13 [ 7002.399170] generic-usb 0003:0C2E:0200.000B: input,hidraw2: USB HID v1.11 *Keyboard* [Honeywell Scanning and Mobility Honeywell Scanning and Mobility Scanner] on usb-0000:00:1d.2-2/input0 [ 7008.463407] usb 8-2: USB disconnect, address 18 [ 7011.780271] usb 8-2: new low speed USB device using uhci_hcd and address 19 [ 7011.957957] usb 8-2: New USB device found, idVendor=0c2e, idProduct=0720 [ 7011.957962] usb 8-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [ 7011.957965] usb 8-2: Product: Honeywell Scanning and Mobility Scanner [ 7011.957968] usb 8-2: Manufacturer: Honeywell Scanning and Mobility [root@pe1800xs ~]# cat /proc/bus/usb/devices T: Bus=08 Lev=01 Prnt=01 Port=01 Cnt=01 Dev#= 19 Spd=1.5 MxCh= 0 D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 P: Vendor=0c2e ProdID=0720 Rev= 1.00 S: Manufacturer=Honeywell Scanning and Mobility S: Product=Honeywell Scanning and Mobility Scanner C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=450mA I:* If#= 0 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=00 Prot=00 *Driver=(none)* E: Ad=02(O) Atr=03(Int.) MxPS= 8 Ivl=10ms E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=10ms -- Thanks & Regards, Manavendra Nath Manav

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Replacing a page in page_cache
by Jack David Feb. 28, 2012

Feb. 28, 2012

Hi All, I am trying to replace a page which is already present in page_cache. Is there any direct way to do so (via some kernel API)? My experiment is something like, I have a file opened and read completely in user space app (just to make sure that all the file is present in page cache). From kernel, I am allocating a new page, filling some data into it, and want to store this data by replacing some existing page from page_cache. Initially I was thinking of removing a page (at a particular index) from page_cache and then add my new page at the same index. But by doing so, that page will be treated as containing invalid data, hence again the data will be fetched from the disk and it will overwrite whatever I had initially written into that page. Is there any way I can add the page into page_cache (by add_to_page_cache_lru) and still mark it Uptodate (SetPageUptodate or something) without any bad consequences? Regards, Jack

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