February 2016 - kernelnewbies@kernelnewbies.org

mkinitcpio
by Tobin Harding Feb. 9, 2016

Feb. 9, 2016

Hi, I have a kernel build question please. After build and install of new kernel and modules mkinitcpio gives the following warning ==> WARNING: No modules were added to the image. This is probably not what you want. Web search did not turn up anything. Complete command and output is: # mkinitcpio -g initramfs-custom.img -k 4.5.0-eudyptula+ ==> Starting build: 4.5.0-eudyptula+ -> Running build hook: [base] -> Running build hook: [udev] -> Running build hook: [autodetect] -> Running build hook: [modconf] -> Running build hook: [block] -> Running build hook: [filesystems] -> Running build hook: [keyboard] -> Running build hook: [fsck] ==> WARNING: No modules were added to the image. This is probably not what you want. ==> Creating gzip-compressed initcpio image: /boot/initramfs-custom.img ==> Image generation successful # Any pointers much appreciated, thank you. Tobin

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Re: mkinitcpio
by Pablo G. Gallardo Feb. 8, 2016

Feb. 8, 2016

Em 7 de fevereiro de 2016 23:07:54 BRST, Tobin Harding <me(a)tobin.cc> escreveu: >> >> Please post every step you took to build the kernel. >> >> Thanks, >> -- >> Pablo G. Gallardo > >Hi Pablo, > >Thanks for the reply. While typing out a response to you with my build >steps I >found the problem > >$ zcat /proc/config.gz > config > >Should have been .config > >Thanks again (I'm emailing you from the new running kernel!) > >Tobin Hello Tobin, Nice! I'm copying the mailing list so if anyone else has this problem, they'll know where to start looking. Regards, -- Pablo G. Gallardo

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Virtual and physical page address
by Mohammad A Khasawneh Feb. 8, 2016

Feb. 8, 2016

Hello everyone, I am attempting to dump the page table of a process in terms of virtual addresses and the corresponding physical addresses. I am looking for information whether the pointers I am using are correct for this purpose: 1. Can I say that pte_page(pte_t) returns the virtual address of the page that the PTE points at? 2. can I say that page_to_phys(struct page) returns the physical address of that same entry? Thank you, Mohammad

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Memory Management
by masoud hematpour Feb. 8, 2016

Feb. 8, 2016

Hi, I am beginner to kernel source. I decide to work on Performance Tuning. I studied some material around memory management but which material is well described for Memory management in Linux? Thank you, masoud

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Re: dma_alloc_coherent
by Vishwas Srivastava Feb. 8, 2016

Feb. 8, 2016

Hi Ran, the api which you have mentioned... void * dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t flag) is the kernel api to alloc consistent memory. DMA devices understand the physical addresses not the virtual addresses. which means that we must supply to the dma device, the physical address, to read from or to write to. The second argument of this api is an input argument which is updated by the kernel if this api returns a success (and contains the physical base address of the allocated memory) and the returned value of this api is the kernel virtual address. if the *CPU* has to operate on this memory (assume that the memory is dma'ed by the dma device and cpu want to read it for further processing ) it should use the virtual address, so the returned value of this api, as the base address. However, if the dma device has to operate on this memory (assume device want to write to this memory), it should use the *dma_handle* , which is the physical address (base) of the dma memory. Now the question is how the dma device knows about this *physical* address? The answer is that the "dma controller" register would have a register to accept this physical address. So the sequence of steps probably would be, in your case: 1: allocate the dma memory 2: programme the dma controller register with the physical address returned by this api, plus the size of the transaction and may be some more registers for setting some kind of flags (depends on your dma device) 3: programme the dma controller's dma *start* bit. after this the dma starts and dma device starts writing to the memory . I hope, this clarifies you. On Sun, Feb 7, 2016 at 10:30 PM, <kernelnewbies-request(a)kernelnewbies.org> wrote: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: dma_alloc_coherent (Ran Shalit) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sat, 6 Feb 2016 21:22:49 +0200 > From: Ran Shalit <ranshalit(a)gmail.com> > Subject: Re: dma_alloc_coherent > To: Denis Kirjanov <kirjanov(a)gmail.com> > Cc: kernelnewbies <kernelnewbies(a)kernelnewbies.org> > Message-ID: > < > CAJ2oMhLi9LV6QQ-Yr1yNKgoBwC_ET-qTwDAGGrDc9BGZLKNNXA(a)mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > On Fri, Feb 5, 2016 at 11:15 AM, Denis Kirjanov <kirjanov(a)gmail.com> > wrote: > > On 2/5/16, Ran Shalit <ranshalit(a)gmail.com> wrote: > >> Hello, > >> > >> I read the readme about dma API, but still don't understand how it > >> should be used > >> It is said that dma_alloc_coherent is responsible for allocating the > >> buffer. > > > >> > >> 1. But how to trigger the dma transaction to start ? > >> 2. Is there a callback when it is finished ? > > > > It's used for data transfer between IO device and system memory. You > > allocate a kernel buffer for DMA transaction (in this case dma from > > device to system memory) and setup your device for dma transfer. An IO > > device usually generates an interrupt when DMA transfer completes. > > Denis > > If I understand correctly the full picture how to use dma is as > following (schematics): > > buf = dma_alloc_coherent(); <<-- done once at the lifetime > > every time we need to trigger dma: > > //start transaction now > writeb(buf, DMA_ADDR) <<- juat an example, actually it is totally > depends on dma device > writeb(START_DMA, DMA_ADDR+2) <<- juat an example, actually it is > totally depends on dma device > > //usually we also register on irq for callback on finishing the > transaction. > > hope I got it all correct, if you have any comments please add. > > Thanks, > Ran > > > > ------------------------------ > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > End of Kernelnewbies Digest, Vol 63, Issue 7 > ******************************************** >

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Process Scheduling
by Nitin Varyani Feb. 8, 2016

Feb. 8, 2016

Hi, I am new to kernel source. I want to plugin a new process scheduling algorithm. Can someone elaborate the steps to do it? Nitin

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TCP_REPAIR code and how it works
by Ramana Reddy Feb. 8, 2016

Feb. 8, 2016

Hi All, Any one have an idea of hwo TCP_REPAIR works, and a working example of a client and multiple servers. Looking forward for your help. Thanks & Regards, Raman

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dma_alloc_coherent
by Ran Shalit Feb. 6, 2016

Feb. 6, 2016

Hello, I read the readme about dma API, but still don't understand how it should be used It is said that dma_alloc_coherent is responsible for allocating the buffer. 1. But how to trigger the dma transaction to start ? 2. Is there a callback when it is finished ? Thank you, Ran

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Sleep_on_buffer
by Harish Feb. 5, 2016

Feb. 5, 2016

Hi, I see this(sleep_on_buffer) in the /proc/<pid>/wchan for a process, could some one help me understand what does this exactly mean? Around this time the thread was actually trying write to the console. The status of the process from /proc says "Disk Sleeping" Thanks, Harish

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How to find a bug with lost network messages
by Sandro Stiller Feb. 2, 2016

Feb. 2, 2016

Hello, I'm struggeling with a network driver (sllin[1]) which is not in the official kernel. It has a lot in common with the slcan driver but is used for LIN networks. The problem is, that sometimes messages sent to the network layer via netif_rx() don't arrive in all listening programs. This is how the driver works: 1. The application sends CAN messages to the network interface 2. The driver forwards it to the UART (tty) 3. The UART receives the same message (single-wire connection, RX and TX connected) and sends it back to the network layer 4. The sending application receives the previously sent message and can check for transmission errors and appended LIN slave replies. Sometimes the last point (4.) does not work after 10 - 40 seconds of transmission. The application does not receive the message using a blocking read() on the socket, but other processes receive it (running candump on the interface). netif_rx() always returns 0. If more programs are listening (running multiple instances of candump), the problem appears less often or never. On my PC there is no problem, it occures on ARM only. I'm using kernel 4.1. Can you give me a hint where to search for the cause of this behaviour? Thank you very much. Sandro [1]: https://github.com/sstiller/sllin/tree/master/sllin

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