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Re: tcp packet split
by Augusto Mecking Caringi Jan. 19, 2014

Jan. 19, 2014

On Sun, Jan 19, 2014 at 2:31 AM, <net.study.sea(a)gmail.com> wrote: > How does the application level recognize each segment bridge in tcp stream > ? > i.e packe a 30bytes>> packet b 50bytes >>packet a 20bytes > And why it is possible for one packet to contain uncontinuous part of > different user protocol packets? > It's not a kernel question in my opinion, but... Take a look here: "Segmentation is the process of carving up information into smaller pieces. The documentation for Transmission Control Protocol (TCP) refrers to what it calls 'data streams'. A data stream is really nothing more than a series of zeroes and ones that represent information. TCP receives data from an application and segments the data into pieces. This segmentation is necessary so that the information can be placed inside the TCP data field." "TCP reassembles segments into a data stream and feeds that data stream to the application. The best known example of this activity is HTTP transfer of a web page. The web server loads a web page from disk, encapsulates the web page text in HTTP headers, the passes the HTTP encoded stream of text to TCP. TCP segments the text stream for transport across the network. The networking software (the stack) receives the TCP data segments and reassembles the HTTP stream of text, which your web browser reads, and renders as a web page." http://www.inetdaemon.com/tutorials/internet/tcp/segmentation.shtml > 在 2014-1-18，22:04，Augusto Mecking Caringi <augustocaringi(a)gmail.com> 写道： > > On Sat, Jan 18, 2014 at 12:08 AM, <net.study.sea(a)gmail.com> wrote: > >> Hi : >> If one tcp data packet contains serveral user protocol packet. . >> How is it splitter over to separate packet ? >> > > Hi, > > It's an application protocol level problem and it's application job to > do this. > > This is also called TCP desegmentation or TCP reassembly. Take a look > here: > > http://wiki.wireshark.org/TCP_Reassembly > > Regards. > > -- > Augusto Mecking Caringi > > -- Augusto Mecking Caringi

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tcp packet split
by net.study.sea＠gmail.com Jan. 18, 2014

Jan. 18, 2014

Hi : If one tcp data packet contains serveral user protocol packet. . How is it splitter over to separate packet ? 发自我的 iPhone

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Question about v4l2 mem2mem driver mem_ops
by m silverstri Jan. 17, 2014

Jan. 17, 2014

Hi, I am working on v4l2 mem2mem driver. I think the sequence of using a V4L2 codec mem2mem driver from user space side is like this: 1. queue buffer for input buffer 2. queue buffer for output buffer 3. Streamon Output plane 4. Streamoff Capture plane 5. dequeue buffer for input buffer 6. dequeue buffer for output buffer And for the driver implementation, I see it needs to setup mem_ops for source and destination queue: for example, http://lxr.free-electrons.com/source/drivers/media/platform/s5p-jpeg/jpeg-c… src_vq->mem_ops = &vb2_dma_contig_memops; dst_vq->mem_ops = &vb2_dma_contig_memops; My question is why we need the mem_ops in source and destination queues. In other woreds, why the driver need to allocate memory when user space applcation has provided the memory via #1 and #2 above? Thank you.

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issue with compiling kernel module
by Arun M Kumar Jan. 17, 2014

Jan. 17, 2014

I am facing the following error message when i try to compile my kernel module. it is a simple hello world module make: Entering directory `/usr/src/linux-3.4.6-2.10' ERROR: Kernel configuration is invalid. include/generated/autoconf.h or include/config/auto.conf are missing. Run 'make oldconfig && make prepare' on kernel src to fix it. make: *** No rule to make target `Device'. Stop. make: Leaving directory `/usr/src/linux-3.4.6-2.10' I have tried the said option, of make oldconfig and prepare... I even recompiled the source using defconfig and am using that kernel, but still i get this error. Please help.

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How to enable VIDEOBUF2_VMALLOC
by m silverstri Jan. 17, 2014

Jan. 17, 2014

Hi, How can I enable VIDEOBUF2_VMALLOC? I try 'make menuconfig', but I don't know how can I configure to enable VIDEOBUF2_VMALLOC: Symbol: VIDEOBUF2_VMALLOC [=n] │ Type : tristate │ Defined at drivers/media/v4l2-core/Kconfig:75 │ Depends on: MEDIA_SUPPORT [=y] │ Selects: VIDEOBUF2_CORE [=y] && VIDEOBUF2_MEMOPS [=n] && DMA_SHARED_BUFFER [=y] │ Selected by: USB_VIDEO_CLASS [=n] && USB [=y] && MEDIA_SUPPORT [=y] && MEDIA_USB_SUPPORT [=n] && MEDIA_CAMERA_SUPPORT [=y] || USB_PWC [=n] && USB [=y] && MEDIA_SUPPORT [=y] && MEDIA_USB_SUPPORT [=n] && MEDIA_CAMERA_SUPPORT [=y] && VIDEO_V4L2 [=y] || VIDEO_STK1160 [=n] && USB [=y] && MEDIA_SUPPORT [=y] && MEDIA_USB_SUPPORT [=n] && MEDIA_ANALOG_TV_SUPPORT [=n] && VIDEO_DEV [=y] && I2C [=y] || VIDEO_EM28XX [=n] && USB [=y] && MEDIA_SUPPORT [=y] && MEDIA_USB_SUPPORT [=n] && (MEDIA_CAMERA_SUPPORT [=y] Thank you.

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kernel driver access application memory
by m silverstri Jan. 17, 2014

Jan. 17, 2014

Hi, If my application allocate memory for input and output buffers, and pass the pointer to a kernel driver (via v4l2 queue buffer operation), can the kernel driver access it? Do I need to setup DMA before teh kernel driver can read/write to it? Thank you.

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ARM Linux and ATAGS
by Mj Embd Jan. 16, 2014

Jan. 16, 2014

Hi, What are atags and are they still used after addition of device tree in linux ? Regards

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About exporting symbols from an external module
by Le Tan Jan. 15, 2014

Jan. 15, 2014

Hello! I am writing a device driver module. I define some functions in the module, for example print_record(). I am doing something in the kvm, so I want to call print_record() in the file of kvm module, for example, I may call print_record() in file /arch/x86/kvm/x86.c to put something into my device driver module. Now comes the question. 1. Where should I put the codes of my device driver module? It's the first time I write the device driver. 2. After compiling my module, I encounter an error when I compile the kvm module. ERROR: "print_record" [arch/x86/kvm/kvm.ko] undefined! I use EXPORT_SYMBOL(print_record) in my module file. I use "extern" to declare print_record() and then call print_record() in file x86.c. To solve this problem, I have tried to copy the Module.symvers from my module folder to /arch/x86/kvm/. But it doesn't work. I have also tried to add *KBUILD_EXTRA_SYMBOLS *to the Makefile of kvm. It doesn't work either. I cat /proc/kallsyms and find that the type of symbol "print_record" is "t" ( local text). What should I do? How to call functions defined in my own module from kvm? Maybe there is something wrong in Makefiles? Any suggestion is appreciated! Thanks!

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Re: Breaking up a bvec in a bio for reading more than 512
by pmkernel Jan. 13, 2014

Jan. 13, 2014

I have a query here. I think using bio you can do scatter-gather operation i.e you do an I/O from multiple locations from disk using bio vector which was a limitation in buffer head. So in this case can you not read multiple sectors in single bio structure with multiple vector entries? Sent from Samsung Mobile -------- Original message -------- From: Rajat Sharma <fs.rajat(a)gmail.com> Date: To: neha naik <nehanaik27(a)gmail.com> Cc: kernelnewbies <kernelnewbies(a)kernelnewbies.org> Subject: Re: Breaking up a bvec in a bio for reading more than 512 I am not sure if I understood your question correctly but there is no scatter-gather semantics in terms of disk/file offsets, I don't think any OS would have implemented such complex thing for no good reason. To implement such thing, it more than just software what it would take to achieve. Disk controller should support such parallelism, which they already do by cylinders, but one cylinder is laid out sequentially in terms of disk _logical_ offset. Regards, Rajat On Mon, Jan 6, 2014 at 1:09 PM, neha naik <nehanaik27(a)gmail.com> wrote: Hi Rajat, I am not opposed to creating multiple bio. I just meant to say that if there is another method which involves not breaking the bio (as i understand breaking the bio) i would love to know it. Regards, Neha On Mon, Jan 6, 2014 at 12:23 PM, Rajat Sharma <fs.rajat(a)gmail.com> wrote: > Why do you want to avoid creating multiple bio? If you have data on multiple > disks, create multiple of them and shoot them simultaneously to get > advantage of parallel IO. And if it is single disk, elevators of lower disk > would do a good job of reading/writing them in serial order of disk seek. I > don't see much of savings with not creating bio, it is going to be allocated > from slab anyways. Also risks you involve with leaving bio in a corruptible > state after customization for one disk are higher. > > > On Mon, Jan 6, 2014 at 10:03 AM, neha naik <nehanaik27(a)gmail.com> wrote: >> >> Hi All, >> I figured out the method by some trial and error and looking at the >> linux source code. >> We can do something like this : >> Say we want to read pages of bvec in 512 chunks. Create bio with >> a single page and read 512 chunk of data from wherever you want to (it >> can be different disks). >> >> dst = kmap_atomic(bvec->bv_page, KM_USER0); ---> bvec is of >> original bio >> src = kmap_atomic(page, KM_USER0); ---> page we read by >> creating new bio >> memcpy(dst+offset, src, 512); >> kunmap_atomic(src, KM_USER0); >> kunmap_atomic(dst, KM_USER0); >> >> My difficulty was not being able to access the high memory page in >> kernel. I was earlier trying to increment the offset of the bvec and >> pass the page to the layer below assuming that it would read in the >> data at correct offset but of course it was resulting in panic. The >> above solves that. Of course, if there is some other method which >> involves not creating any bio i would love to know. >> >> Regards, >> Neha >> >> >> On Sat, Jan 4, 2014 at 9:32 AM, Pranay Srivastava <pranjas(a)gmail.com> >> wrote: >> > >> > On 04-Jan-2014 5:18 AM, "neha naik" <nehanaik27(a)gmail.com> wrote: >> >> >> >> Hi All, >> >> I am getting a request with bvec->bv_len > 512. Now, the >> >> information to be read is scattered across the entire disk in 512 >> >> chunks. So that, information on disk can be : sector 8, sector 100, >> >> sector 9. >> >> Now if i get a request to read with the bvec->bv_len > 512 i need to >> >> pull in the information from >> >> multiple places on disk since the data is not sequentially located. >> >> I tried to look at the linux source code because i think raid must be >> >> doing it all the time. (eg : on disk 1 we may be storing sector 6 and >> >> on disk 2 we may be storing sector 7 and so on). >> > >> > You are right. Perhaps you need to clone the bio and set them properly. >> > I >> > guess you ought to check dm driver's make_request function. It does >> > clone >> > bio. >> > >> > I don't know if you can split that request while handling it. Perhaps >> > reinserting that request could work. >> > >> >> However, i have not really got any useful information from it. Also >> >> scouring through articles on >> >> google has not helped much. >> >> I am hoping somebody points me in the right direction. >> >> >> >> Thanks in advance, >> >> Neha >> >> >> >> _______________________________________________ >> >> Kernelnewbies mailing list >> >> Kernelnewbies(a)kernelnewbies.org >> >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > >> > ---P.K.S >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Kernel Network Subsystem Patching
by Aruna Hewapathirane Jan. 11, 2014

Jan. 11, 2014

Hi, I am a newbie to kernel hacking and I have a question. Am trying to patch the Network Subsystem and changing the net_random() to direct calls of prandom_u32. Why ? Because it is harder to audit / grep and new commits actually use prandom_u32 only am told. u32 prandom_u32(void); /* defined in include/linux/random.h: */ #define net_random() prandom_u32() /* defined in include/linux/net.h */ Everything works as expected until I get to net/core/neighbour.c and then patch fails to apply. The diff is here: ------------------------------------------------------------------------------------------------------------------------------- diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 47d834e..ea97361 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -117,7 +117,7 @@ static void neigh_cleanup_and_release(struct neighbour *neig unsigned long neigh_rand_reach_time(unsigned long base) { - return base ? (prandom_u32() % base) + (base >> 1) : 0; + return base ? (net_random() % base) + (base >> 1) : 0; } EXPORT_SYMBOL(neigh_rand_reach_time); @@ -1415,7 +1415,7 @@ void pneigh_enqueue(struct neigh_table *tbl, struct neigh_ struct sk_buff *skb) { unsigned long now = jiffies; - unsigned long sched_next = now + (prandom_u32() % + unsigned long sched_next = now + (net_random() % NEIGH_VAR(p, PROXY_DELAY)); if (tbl->proxy_queue.qlen > NEIGH_VAR(p, PROXY_QLEN)) { ------------------------------------------------------------------------------------------------------------------------------- I can use some help and guidance please, what am I doing wrong ? Or not seeing ? It's just this neighbor.c file that is doing this and I am stumped. Thank you. Aruna Hewapathirane <https://sites.google.com/site/arunahewapathirane/home/business-card/buisnes…>

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