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[PATCH 0/1] staging: wilc1000: need feedback about a patch
by Raphaël Beamonte Aug. 17, 2015

Aug. 17, 2015

Hello there, I just started patching some drivers to familiarize myself better with the kernel and perhaps contribute more to it if I find things that I can actually handle! (hoping I'll be able to handle more and more throughout time). Doing so, I found out that in the wilc1000 (staging) driver, I got compiler warnings for casts from u32 variables to pointers and pointers to u32 variables. Of course, as my system is 64 bits, the pointers are stored on that format, while u32 is stored on only 32 bits, making this cast insecure. Replacing the u32 variables by size_t ones corrects this behavior, as size_t is stored on 32 bits for 32 bits systems and 64 bits for 64 bits systems. But I'm wondering if doing so breaks everything here? I mean, why use u32 instead of int at first if 32 bits wasn't needed? Also, there is a variable named u32address, which clearly states that u32 was researched here. So, you'll find following this email the patch I made for the file host_interface.c which was reporting these warnings a lot. I'd like to get some advice on that patch: is it a good idea to do that? If so, can I improve it? If no, what can I do differently to correct those warnings? I'm here to learn, all feedbacks are welcome! Once everything is figured out on how to correct that, I'll be happy to apply that correction to the other files of the modules that still report that warning! Thanks, Raphaël Raphaël Beamonte (1): staging: wilc1000: replace addresses variables type from u32 to size_t for x64 systems drivers/staging/wilc1000/coreconfigurator.c | 2 +- drivers/staging/wilc1000/coreconfigurator.h | 2 +- drivers/staging/wilc1000/host_interface.c | 126 ++++++++++++++-------------- drivers/staging/wilc1000/host_interface.h | 2 +- 4 files changed, 66 insertions(+), 66 deletions(-) -- 2.1.4

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[RFC] Implementing an additional TCP congestion control algorithm (TCP-PR) - communication and organisation.
by Richard Sailer Aug. 17, 2015

Aug. 17, 2015

Hello, I'm Richard Sailer and I've started implementing an alternative congestion control algorithm for linux, capable of maintaining high throughput during persistent packet reordering (TCP-PR). Before continuing my learning and work I want to send a coordinative mail to the netdev list to: * Ask whether this algorithm is wanted in general and will be merged * To synchronize and communicate my work with the other subsystem developers and maintainers. And this organisational and communication-specific part is where I need help, the technical part is fine so far. I have been unsure for long and put quite some effort in writing the following mail (see next section), including letting several colleagues review it. It would be a great help for me, if you could (even if just shortly) review the mailtext and tell me your opinion. Please do not answer the questions in the mail, they're somehow meant as discussion starters for the netdev list. And I have two questions regarding organisation: 1. I usually GPG sign all my Mails for work or academica. I recognised most netdev users don't. Which behaviour is correct? Should I sign my Mail? 2. Is directly asking for a mentor appropriate? Since I'm quite used to reading literature, documentation or source code and figuring things out myself this would mean little effort in "parenting" :p. It would mostly boil down to review my code once a week or less and consulting me on design designs (like tradeoffs), since I would try to ask as less as possible and cause as less extra work as possible. == The Mail == Subject: Implementing an additional alternative TCP congestion control algorithm (TCP-PR) Hello, I'm Richard Sailer and I want to implement and maintain an additional congestion control algorithm for linux, capable of maintaining high thourghput during persistent packet reordering (TCP-PR). The main purpose of this mail is to organize, synchronize and communicate this work *before* I start the coding, to avoid a situation and patch, you and I would be unhappy with. == About me == I'm a 23 year old computer science student and programmer, living and studying in Augsburg, germany. Also I'm working for an IT company in munich as a freelancer. I've specialized on reading, understanding and maintaining existing legacy code. Sadly the most legacy code I'm currently dealing with is written in perl. I would describe myself as a diligent, perfectionistic and slow programmer. I like and use unixoid operating systems for several years now. I've been interested in computer networking for a long time and therefore chose my bachelor thesis on multipath tunneling (other name: osi layer 3 link aggregation). During my experiments I observed that these aggregation produces severe packet reordering and several TCP implementations available dealt quite bad with it. (details see next section). After searching for reordering robust TCP variants I discovered TCP-PR and a implementation for linux 2.4.18. == About TCP-PR == TCP-PR is an alternative congestion control algorithm. Since it doesn't use DUPACKs at all to detect packet loss, packet reordering has no big impact on the goodput. This way the following 2 things can not happen: 1. out-of-order ACK segments get recognized as DUPACKs - these mean spurious retransmit and reducing of cwnd 2. out-of-order data segments won't trigger sending of DUPACKs - actually even if this happens the sender just ignores these DUPACKs therefore a sender-side only implementation of TCP-PR is sufficient. But therefore all packet losses have to be detectet by timeouts, which means different timeout definitions and handling mechanisms have to be applied. Mainly this means that any timeout reduces cwnd to cwnd/2 instead of setting it to 1. Also RTO adjustment is callculated differently. While all this may sound like big changes from TCP Cubic or New Reno, during algorithm design, a great amount of work was invested in making TCP-PR behave throughput-fair to other TCP variants on the same network. This has also been validated by excessive ns-2 simulations. The exact results of these simulations as well as further details of the timeout definitions and other aspects of the algorithm can be found in the original paper at: www.ece.ucsb.edu/~hespanha/published/366Bohacek.pdf If requested I'm happy to describe more details of tcp-pr, it's algorithm and RTO definitions. Also a closer discussion and comparison to TCP Cubic or New Reno (with or without adjusted DUPACK settings set in /proc/ ) is possible but I wanted to keep this first mail (relatively) short. == Some Questions == 0. In general, is this congestion control algorithm of interest for you? Does it have a fair change of beeing merged, assumed: * I provide a clean and documented implementation * I apply all adjustments and improvements requested 1. From reading netdev-FAQ.txt I assume I should use *net-next* as my base for coding and testing. Is this correct? 2. Is *testing* my patches against net-next kernels sensible? Or should I use the torvalds or stable tree for sound tests? 3. I'm currently using paravirtualized Xen VMs for most of my virtualization needs. Is using Xen PV for testing my TCP extension a good idea? I think it's not problematic but I'm not entirely sure. 4. Do you prefer to get this whole patch via Email or by somehow interacting with a git repository? I think setting up a git repository would make a continuous review process before finally merging easier, which I would like. If I set up a repository mirror, is there any webinterface or server side software you would prefer or recommend. I suppose you don't like using github for that purpose. 5. In the documntation file networking/tcp.txt there is a section called: How the new TCP output machine [nyi] works. =========================================== Is the [nyi] still true? The file says: "last updated february 2008". Can I rely on this information or is it better to look elsewhere and/or in the source code? If during my work and reading/understanding the relevant code, I would update this and perhaps other documentation I stumble uppon is this something appreciated or wanted? 6. I'm currently reading "practical C programming" and severeal of the doc files in the kernel repo. Are there any further books you would recommend for me? I have already read "Unix Network Programming" by stevens, and own a copy of Tanenbaums "Computer Networks" and "Operating Systems" books. Thanks -- Richard

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Re: Why is SECTOR_SIZE = 512 inside kernel ?
by Navin P Aug. 17, 2015

Aug. 17, 2015

On Mon, Aug 17, 2015 at 10:46 PM, <Valdis.Kletnieks(a)vt.edu> wrote: > On Mon, 17 Aug 2015 16:35:59 +0530, Navin P said: >> Hi, >> Why is SECTOR_SIZE 512 ? > > Because most fixed-block devices presented a logical interface in terms > of 512 byte sectors. (IBM's count-key-data format is an example of a non-fixed > block device). > >> Is it going to change or is it cast in stone ? > > As you have probably figured out, high-capacity devices have often moved > to 4K physical blocks to avoid wasting so much room between blocks (the hardware > format includes a preamble to each block and a postamble, and dead space in > between, it uses more space than you think). > > However, as long as there are still devices out there that have 512 byte > blocks, it's not changing. And it still won't change unless there's a > good reason to change it (hint - how many places in the kernel have hidden > assumptions about the size of SECTOR_SIZE being 9 bits worth?) I posted this to http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg956881.html avoided cross posting. Looks like this is cast in stone at kernel . I was thinking of doing sectors written * hw_sector_size. But the sectors counters in /proc/diskstats are actually 512 byte sections even for 4kN disks. That way userspace programs are immune to underlying sector. Wish that page_size was also same :) There are lot of places like 9 bits . http://lxr.free-electrons.com/source/block/blk-lib.c bio->bi_iter.bi_size = req_sects << 9; http://lxr.free-electrons.com/source/include/linux/blkdev.h sprinkled with 9 . I'm assuming the magic number 9 here is SECTOR_SIZE. :) The hw_sector_size must be cosmetic in that sense or just to you tell you that "your drive really is 4kn" or "512e".

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Re: [PATCH 1/1] staging: wilc1000: replace addresses variables type from u32 to size_t for x64 systems
by Raphaël Beamonte Aug. 17, 2015

Aug. 17, 2015

2015-08-17 13:12 GMT-04:00 <Valdis.Kletnieks(a)vt.edu>: > If you're going to do this, do it *right* and chase down where all these > variables are defined and nail them down to a size_t *there* so you can get rid > of most of these casts - plus potentially find *other* places they're playing > fast and loose with the types. You're right. I tried first to use the struct that is used to declare pstrWFIDrv, but as it needed a lot of code refactoring I switched to find an easier path, but that's not as elegant and clean. > Umm.. this isn't for a brain-dead card that has to have its addresses > down in the the first 4G of memory, is it? Or was the driver author > stuck on a 32-bit kernel? Actually, that's what I wondered also! With further researchs, I just ended up finding those patches in the linux-wireless mailing list: http://www.spinics.net/lists/linux-wireless/msg138655.html http://www.spinics.net/lists/linux-wireless/msg138656.html These patches are not integrated with Greg's staging tree yet it seems. That's probably why I missed them at first... They however seem more clean than mine.

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Why is SECTOR_SIZE = 512 inside kernel ?
by Navin P Aug. 17, 2015

Aug. 17, 2015

Hi, Why is SECTOR_SIZE 512 ? http://lxr.free-electrons.com/source/include/linux/ide.h#L118 http://lxr.free-electrons.com/source/include/linux/device-mapper.h#L548 548 #define SECTOR_SHIFT 9 I was looking at disks with hw_sector_size . Most of them i looked at had 512 bytes except for one which had 4096 (virtual disk). The one with AF format ie has logical sector size as 512 and hw_sector_size as 512 . So it is fine for my calculation from /proc/diskstats. But the one with 4096 logical and 4096 physical i multiply hw_sector_size with the sectors read and written but that is wrong since the kernel always defines sectors in terms of 512. Is it going to change or is it cast in stone ? Here is an example. Again this is a VM virtual disk. vdc is the subject in interest. [root@hphuge-049 ~]# fdisk -l /dev/vdb /dev/vdc Disk /dev/vdb: 21.5 GB, 21474836480 bytes, 41943040 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/vdc: 17.2 GB, 17179869184 bytes, 4194304 sectors Units = sectors of 1 * 4096 = 4096 bytes Sector size (logical/physical): 4096 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes [root@hphuge-049 ~]# [root@hphuge-049 ~]# cat /sys/block/vdc/queue/hw_sector_size && cat /sys/block/vdc/queue/logical_block_size && cat /sys/block/vdc/queue/physical_block_size 4096 4096 4096 [root@hphuge-049 ~]# cat /sys/block/vdb/queue/hw_sector_size && cat /sys/block/vdb/queue/logical_block_size && cat /sys/block/vdb/queue/physical_block_size 512 512 4096 [root@hphuge-049 ~]# Regards, Navin

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Kernel Debugging using Qemu
by Aruna Hewapathirane Aug. 16, 2015

Aug. 16, 2015

Hi, If anyone uses Qemu can someone please show me how to get started ? I tried : sudo qemu-system-x86_64 -s -S -kernel arch/x86/boot/bzImage -initrd /boot/initrd.img-4.1.2-vtaqemu+ /dev/zero And it does allow me to access through gdb using target remote localhost:1234 but when I set a breakpoint in kernel_start and continue it hangs and tells me /bin/sh: can't access tty; job control turned off ? I am runing a Debian 4.1.2 custom kernel. I have enabled Intel virtulization in the bios. And menuconfig have setup virtualization. After many tries have finally managed to get this far but now I can use all the help I can get. And and all suggestions, guidance, *pointers are most welcome. Thanks - Aruna

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vmlinux
by Gnoleba GNOGBO Aug. 16, 2015

Aug. 16, 2015

Hi All ! In my learning of linux there is the stupide questions i would like to ask you. 1- Why the name of the kernel is vmlinux ? What is the origine of this name ? Perhaps you know why ? Tell me please or give the link which can explan it. 2 - When linux start the init process launch the default shell process and give the prompt. The others process as linux commands or users process are the forks of this first shell process ? Can you explan simply this point or give me the link which can help me please in the starting of linux. Do something as everybody is good but know why, is better to do it. Help please. Gnogbo

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Best approach to explore the linux source code
by Umair Khan Aug. 16, 2015

Aug. 16, 2015

Hi everyone, I'm a final year undergraduate student. I've been spending a lot of time with OS books these days. I've been reading about the internals of the Linux kernel and drivers in the books. But, I've never really seen them in action except the drivers. Hacking a driver is easy. Is there any good approach/tutorial to walk me through the source code of the kernel ? Also, I'm using a self built linux kernel 4.2 on my laptop. Is there any way that I can contribute upstream to the kernel. I'm using 4.2 in the hope to find bugs in driver stuffs. I haven't found any yet. Thanks Umair Delhi Technological University, India

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Windows Vs Linux - Whats the "Reality"
by Sasha Mckinsey Aug. 15, 2015

Aug. 15, 2015

Hi, came across this discussion thread so thought should share it get the views of the community. I dont agree with all the points mentioned fully but some of the points do make sense. Here it is : Question 1 :Why do people always advise to learn Linux and not windows. Questions 2 : Why people always advise budding programmers to learn and deep dive in Linux kernel source code. Windows programmers do equally fine without windows source code. Some facts as I understand : Linux is open source and code is available for better understanding Linux is secure and used on most of the servers Flexible and can be customized/configured as per the needs However, desktop space is ruled by "Windows". 92% users use windows on desktop. Virus/ malware are made primarily to target windows corporates have windows on desktops and servers too Most of the software gaints hire "more" people with windows background because thats where the money is. All the programmers who make open source applications for Linux eventually end up porting the application to windows as well...perhaps for monetary benefits. One might argue that Windows sales have stagnated and mobile / tabs are picking up but that another Argument All views would be welcome ! Discussion thread source: http://cboard.cprogramming.com/linux-programming/167804-windows-versus-linu…

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which means these lines (CFS)
by Meyer Lansky Aug. 15, 2015

Aug. 15, 2015

Thank you very much!! You, as always saves me.

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