July 2014 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Xserver on framebuffer (/dev/fbX)
by Praveen Kumar Pendyala July 8, 2014

July 8, 2014

Hello, I have a kernel framebuffer driver which creates a new framebuffer device at /dev/fbX (X = 1 or 2 generally). Now I want to run a Xserver on this framebuffer. Can someone please give some pointers on how to do this? My code is available at https://github.com/praveendath92/udlfb (a fork of displayLink kernel driver) I'm attempting a USB remote display for linux. Any help is greatly appreciated. Thanks. Best, Praveen, http://praveenkumar.co.in

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current->exit_code Where does this get initialised?
by manty kuma July 8, 2014

July 8, 2014

Hi, Consider a scenario that a signal handler is getting executed and also ptrace is attached to the process in parallel. I have following queries : 1. If a signal is sent to the process from signal handler, Will the signal be delivered and handled(With ptrace already attached)? 2. what is current->exit_code here <https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/kernel…> ? If this is the exit code of the application, is it properly initialized at this point in time(while the signal is being delivered)? If yes, could someone help me spotting it in source? Looking forward for responses. Thank you Best Regards, Manty

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DMAR:[fault reason 02] Present bit in context entry is clear error
by Ahmed A July 7, 2014

July 7, 2014

Hello, I have a Supermicro motherboard - Kingstar X9DRW-iF (http://www.supermicro.com/products/motherboard/Xeon/C600/X9DRW-iF.cfm ), CPU present in both sockets. I have a FC hba inserted in the right slot (based on spec of motherboard,), which is connected to CPU2 / Socket 1. I unloaded the FC hba driver, and bound the hba device/ports to vfio using the programming API mentioned in vfio doc - https://www.kernel.org/doc/Documentation/vfio.txt. I am using a default container, with one group in it, which contains both ports of the hba (one PCI function per port). After I issue the first command to hba, when hba attempts to download (Read) a fw image from host memory, I am getting a DMAR error: /var/log/syslog:9:Jul 7 08:29:11 host-11 kernel: [569259.473862] dmar: DRHD: handling fault status reg 202 /var/log/syslog:10:Jul 7 08:29:11 host-11 kernel: [569259.535230] dmar: DMAR:[DMA Read] Request device [05:00.1] fault addr 7fffe85e9000 /var/log/syslog:11:Jul 7 08:29:11 host-11 kernel: [569259.535230] DMAR:[fault reason 02] Present bit in context entry is clear From talking to people, it might be due to the IOMMU table not being correctly programmed. Can someone please give me some pointers which kernel function / data structure to look at to root cause the issue. Thank you, Ahmed.

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Re: USB file mmap
by Greg Kroah-Hartman July 7, 2014

July 7, 2014

On Tue, Jul 08, 2014 at 01:26:26AM +0530, Jeshwanth Kumar N K wrote: > Hi Greg, > > Thanks for the reply. > > I recently purchased an mbed board > https://mbed.org/platforms/mbed-LPC1768/ (friend recommended) to learn > USB Mass storage class. And used OpenLPC usb stack with fatfs example > to check how it works (used protocol analyser and stuff, to know whats > happening). In that they are reading each buffer, i mean copying > buffer (8k) of data to RAM and process it. And other idea I found is > using diskio function in openLPC stack to read the data in USB flash > (but this is without file system). The USB storage protocol does not define a specific filesystem, so you can send "raw" block commands to the device, but that's usually not very interesting. > As a Linux user I knew in Linux we can do mmap easily for a file (with > filesystem). So thought of asking from where to start understanding > these concepts :). mmap on a file on disk is the same as USB flash, a USB storage device is just a SCSI device (a quite complex little device, not a trivial one at all.) As I said, you have a filesystem, block layer, SCSI layer, USB layer, and then the VFS and other stuff going on here. So I'd recommend focusing on one layer at a time, otherwise you will be overwhelmed. good luck, greg k-h

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USB file mmap
by Jeshwanth Kumar N K July 7, 2014

July 7, 2014

Hello List, I am trying to understand mmap on files residing in USB flash, so can you please give a pointer from where I can start to understand this? I mean how it works, and which part in kernel takes care of it. Thanks

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differences between async_schedule and async_schedule_domain
by vichy July 6, 2014

July 6, 2014

hi all: I have some questions about: 1. what is the difference between async_schedule and async_schedule_domain 2. when the program is triggered when it is registered as async_schedule and async_schedule_domain is it triggered at softirq stage? thanks for your help in advance,

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Getting an obscure driver into mainline
by Kieran Kunhya July 4, 2014

July 4, 2014

Hello, I have reverse engineered a driver for Sony SxS memory cards which are expresscards used in professional cameras. Unfortunately I haven't figured out how to make it work with DMA as used in the block device API; currently it only works with a memcpy. I'm not really sure if I'm using the block device API incorrectly and was told to ask here (and cc GKH) since I didn't hear much from lkml. My code is here: https://github.com/kierank/sxs-linux What is the next step for getting this into mailing and who is the person to ask about block device DMA? Kieran

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How to use keyring in the kernel?
by Freeman Zhang July 4, 2014

July 4, 2014

Hi List! Recently I want to play with kernel keyring facilities. But I find out that only a few programs like eCryptfs using kernel keyring. I read the documents. It said: The key service defines two special key types: (+) "keyring" Keyrings are special keys that contain a list of other keys. Keyring lists can be modified using various system calls. Keyrings should not be given a payload when created. (+) "user" A key of this type has a description and a payload that are arbitrary blobs of data. These can be created, updated and read by userspace, and aren't intended for use by kernel services. Does it means we keep the keyring in the kernel only for userspace programs to use? How can this strategy ensure security? And most importantly, what if someone need to manipulate (created, updated and read) keys(not keyring) in kernel services while user key type "aren't intended" for that? All the best! Freeman

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Eudyptula Challenge
by me storage July 3, 2014

July 3, 2014

Hi i have checked all the documentation for the task 4. I gone through all chapters. Before submitting the challenge, i checked my files with ' checkpatch.pl ' but it doesn't shows any errors. Even though not getting any errors the challenge is not being completed. So can anyone guide me if any other documents are there to be refer by me. Thank you

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DMA over USB
by Raghavendra July 2, 2014

July 2, 2014

Hello, I have a query regarding DMA(Direct Memory Access) for the usb devices. The understanding of DMA actions over PCI is straight forward. PCI devices support bus mastering capability, such that the PCI devices could take the ownership of the bus and perform access to the memory directly, and a software support exists for the same in Linux. As far as USB devices are concerned, they don’t have the bus mastering capability like the PCI devices. But the USB URB structure have a field named 'dma_addr_t transfer_dma', used for DMA access. The USB driver allocate the DMA buffers coherently and pass the DMA address to the URBs during its initialization. As far as Linux is concerned, how the DMA action being taking place for USB devices. As per my understanding, the USB host controller is taking care of the DMA operations. But I require a little more insight into it. Further more, if it is possible for the USB devices, then can this support be also extended towards low-end protocols such as I2C or SPI? Thanks, Raghavendra ------------------------------------------------------------------------------------------------------------------------------- [ C-DAC is on Social-Media too. Kindly follow us at: Facebook: https://www.facebook.com/CDACINDIA & Twitter: @cdacindia ] This e-mail is for the sole use of the intended recipient(s) and may contain confidential and privileged information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies and the original message. Any unauthorized review, use, disclosure, dissemination, forwarding, printing or copying of this email is strictly prohibited and appropriate legal action will be taken. -------------------------------------------------------------------------------------------------------------------------------

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