- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

block mailing list?
by Raymond Jennings March 15, 2013

March 15, 2013

Is there a kernel list dedicated to discussion of block devices?

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Need of different memory zones
by Niroj Pokhrel March 15, 2013

March 15, 2013

Hi All, I have been studying Memory Management in linux. But I am confused with the division of different ZONE. The use of ZONE_DMA and ZONE_NORMAL is fine. But I am confused with ZONE_HIGHMEM, if the system is 32 bit then why can't it map 4GB memory (2^32). I had thought that ZONE_NORMAL was for the kernel usage so directly mapped and ZONE_HIGHMEM for the user process and is not directly mapped to facilitate virtual addressing. But I know I am not getting something right. While going through Ch - 15 of Rubini's Linux Device Driver (Memory Management and DMA) I came across following line "a 64-bit architecture such as Intel’s x86-64 can fully map and handle 64-bits of memory.Thus, x86-64 has no ZONE_HIGHMEM and all physical memory is contained within ZONE_DMA and ZONE_NORMAL." So, if it can be directly mapped why not in 32 bit architecture. I am really confused. Please Help. Thanking you in Advance Yours, Niroj Pokhrel

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[ARM-LINUX] Quiry regarding the DMA mapping.
by sandeep kumar March 15, 2013

March 15, 2013

Dear All i have one question regarding DMA mapping. i know that dma_alloc* API does the mapping for DMA' able memory. But is it the only way to get dma'able memory? Can we do a dma to pmem or ion reserved heaps as well, right away without dma_alloc?(this also assures us the physical contigious region) -- With regards, Sandeep Kumar Anantapalli,

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networking question
by devendra.aaru March 15, 2013

March 15, 2013

Hey all, I have got a strange bug(?) while testing the multicasting server and client. I have done only the INADDR_ANY bind in server and client adds its IP_MULTICAST_IF to 224.0.0.1 , surprisingly i recvd pkts from the client with out joining using IP_ADD_MEMBERSHIP. Is that a bug? or as we listening on INADDR_ANY will make us recv all the mcast/bcast pkts? while if i do tx on 224.0.0.3 , the server is not able to recv the packets. any ideas?

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When to use blk_end_request_* routines.
by Pranay Kumar Srivastava March 14, 2013

March 14, 2013

Hi, I'm using SLES11-SP1 kernel 2.6.32 .12-0.7 I wrote a block driver for an in-memory disk. The driver seems to work fine however sometimes when I try to unload the driver the machine freezes, the module_exit code looks like the following, /*We take no more requests!*/ spin_lock_irqsave(&pks_disk->queue_lock,flags); blk_stop_queue(pks_disk->pks_disk_rqq); spin_unlock_irqrestore(&pks_disk->queue_lock,flags); /*Remove disk*/ del_gendisk(pks_disk->pks_disk_gd); /*free queue*/ blk_cleanup_queue(pks_disk->pks_disk_rqq); I searched around and found out that while processing the requests from request queue you've got to use one of the blk_end_request* functions (which I did). However if I only use a) blk_end_request: The module removal code freezes machine. b) blk_end_request_cur: The module removal code works fine. There's one more c)blk_end_request_all: Didn't used this one cuz the above one worked :P. I digged around in the source and found this function blk_update_request and in the comment section it says " Actual device drivers should use blk_end_request instead" which I did and the driver module didn't liked it when I tried to remove it :( Now I'm confused as I've got no clue when to use which function can anyone give some examples please? --P.K.S ::DISCLAIMER:: ---------------------------------------------------------------------------------------------------------------------------------------------------- The contents of this e-mail and any attachment(s) are confidential and intended for the named recipient(s) only. E-mail transmission is not guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or may contain viruses in transmission. The e mail and its contents (with or without referred errors) shall therefore not attach any liability on the originator or HCL or its affiliates. Views or opinions, if any, presented in this email are solely those of the author and may not necessarily reflect the views or opinions of HCL or its affiliates. Any form of reproduction, dissemination, copying, disclosure, modification, distribution and / or publication of this message without the prior written consent of authorized representative of HCL is strictly prohibited. If you have received this email in error please delete it and notify the sender immediately. Before opening any email and/or attachments, please check them for viruses and other defects. ----------------------------------------------------------------------------------------------------------------------------------------------------

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Unlocking task_list read lock before performing a sleepy operation
by Pranami Bhattacharya March 14, 2013

March 14, 2013

Dear All, I was trying the following and had a doubt. >From my kernel module I want to iterate over task list and do some sleepy operation for all the process for which my task->flag is set .I know by holding read_lock(tasklist_lock)/rcu_read_lock I should not be performing any sleepy operation. So I have coded like below : 1. Take the read lock 2. Iterate over task (for_each_process) 3. If my flag is set I unlock the tasklist_lock and get_task_struct 4. Perform the sleepy operation 5. Then put_task_struct 6. Again take read_lock(&tasklist_lock); 7. Loop continues The code snippet is as shown below : read_lock(&tasklist_lock); for_each_process(c) { if (c->my_flag) { read_unlock(&tasklist_lock); get_task_struct(c); ... perform_sleepy_operation(); ... put_task_struct(c); read_lock(&tasklist_lock); } } Please let me know if this approach is correct. Thanks and Regards, Pranami

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nmi_watchdog kernel parameter is set but NMI interrupts are not incremented
by Kevin Wilson March 13, 2013

March 13, 2013

I read the nmi_watchdog section in http://lxr.free-electrons.com/source/Documentation/sysctl/kernel.txt I tried booting with nmi_watchdog=2 and with nmi_watchdog=1. In both cases I did not see that the NMI interrupts are incremented (cat /proc/interrupts showed 0 0 for NMI) I saw on the web the most new computers from the last 2-3 years should have support for using nmi_watchdog. I am using Fedora 18. (x86_64) I would appreciate if someone (preferably more than one) will try to boot with nmi_watchdog=2 and will report the result. rgs, Kevin

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Implementing Network Packet Capturing in Linux-3.5.7
by Prasad Lakshman March 13, 2013

March 13, 2013

Hi, I am trying to implement packet capturing in Linux-3.5.7. I have the procedure which works in Linux-2.4 , will the same procedure work on Linux-3.5.7 I am bit new to this , the procedure i am following is implementing Netfilter hooks capture the packets at several points of path in TCP/IP protocol stack NF_IP_PRE_ROUTING 1st hook NF_IP_LOCAL_IN 2nd hook NF_IP_FORWARD 3rd NF_IP_POST_ROUTING 4th NF_IP_LOCAL_OUT 5th Each hook is activated. Kernel modules can register to listen at any of these hooks. 1. NF_ACCEPT . 2. NF_DROP . 3. NF_STOLEN . 4. NF_QUEUE . 5. NF_REPEAT . does this procedure work with the new kernel version also now from user space i am going to use Libipq I for communicating with ip_queue. Please someone let me know if i am missing something, Regards, Blprasad.

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BUG: unable to handle kernel paging request EIP is at kmem_cache_alloc when testing a new bluetooth driver
by Ahmed Abdelfattah March 13, 2013

March 13, 2013

Hello , I am writing a kernel module to abstract a Bluetooth USB dongle as a character device (using btusb as a base for my work) so that the user space bluetooth stacks (like the new broadcom stack released in Android 4.2) can communicate with the Bluetooth USB device. I tested the driver by a writing simple HCI reset command and monitoring the HCI event my driver works OK for a short time but then the kernel randomly panics after undetermined number of loops writing reset and reading an event . The EIP is always at kmem_cache_alloc but with different stack traces. my guess is that I am somehow corrupting the memory but I can't really determine how to debug because the kernel doesn't break in my code but as I mentioned before I get usually a different stack trace. Here is is an example pastebin.com/9jhUuaDn and another log pastebin.com/Ftzju4BZ Any idea what can cause this panic or how to debug it ? -- regards , Ahmed Abdelfattah

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pthread_lock
by ishare March 13, 2013

March 13, 2013

when pthread_unlock(mutex) is called , do other threads waiting for mutex be waked up immediately? or be waked up at the next schedule?

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