September 2013 - kernelnewbies@kernelnewbies.org

Dcache_lock replacement
by Saket Sinha Sept. 5, 2013

Sept. 5, 2013

I have a driver which I have ported from 2.6.18 kernel to 3.8 kernel. Now the driver has become unstable when I ported it to 3.8 kernel. Since lot of things have changed from 2.6.18 to 3.8 and I have taken a lot of care to replace the old kernel APIs with the newer ones but then too there have been certain things I haven't been able to replace and dcache_lock is one of them. Due to the absence of dcache_lock, I have not been able to properly lock stuff and writing/reading data that are being changed that maybe one of the reasons for instability. I specifically list down the link to my kernel driver below where I haven't been able to do the same, below- https://github.com/HeisSpiter/hepunion/blob/master/fs/hepunion/helpers.c#L3… If someone can suggest an alternative, I shall be grateful. Regards, Saket Sinha

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[PATCH 1/1] Squashfs-Optimized-uncompressed-buffer-loop-v3
by Manish Sharma Sept. 4, 2013

Sept. 4, 2013

Signed-off-by: Manish Sharma <manishrma(a)gmail.com> --- fs/squashfs/block.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c index fb50652..41d108e 100644 --- a/fs/squashfs/block.c +++ b/fs/squashfs/block.c @@ -167,17 +167,14 @@ int squashfs_read_data(struct super_block *sb, void **buffer, u64 index, /* * Block is uncompressed. */ - int i, in, pg_offset = 0; - - for (i = 0; i < b; i++) { - wait_on_buffer(bh[i]); - if (!buffer_uptodate(bh[i])) - goto block_release; - } + int in, pg_offset = 0; for (bytes = length; k < b; k++) { in = min(bytes, msblk->devblksize - offset); bytes -= in; + wait_on_buffer(bh[k]); + if (!buffer_uptodate(bh[k])) + goto block_release; while (in) { if (pg_offset == PAGE_CACHE_SIZE) { page++; -- 1.7.9.5

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RE: Introducing Myself, Looking to Learn
by Varad Gautam Sept. 4, 2013

Sept. 4, 2013

> I have external sata to usb3 adapter that is not supported by the > kernel. I'm willing to buy one for someone willing to get the kernel > support done. > - > This is my second offer. No takers the first time. > > Fyi: I expect no true code is needed, just updating a pid / vid table > somewhere. I don't know the usb driver stack so I have no idea where > said table is. > > Fyi2: I tend to focus on filesystems recently so diving into usb is not > a goal of mine. > > Greg Hi Greg, thanks for the offer. I'd be happy to. I shall let you know once I catch some speed, and then I'll start.

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Re: Info Virtual Rootkit Blocker
by Anuz Pratap Singh Tomar Sept. 4, 2013

Sept. 4, 2013

On Wed, Sep 4, 2013 at 4:59 AM, Shubhashish Behera < shubhashish_001(a)yahoo.co.in> wrote: > There is a ongoing project is present under the kernel projects. > > > > http://kernelnewbies.org/KernelProjects/VirtRootkitBlocker?highlight=%28Cat… > > Ok, First things first, do not top post and remove all html markings from your mails. Please send text only mails. Secondly, it is a tentative project(or donno if Rik has done some work on it already) and you are asking a very generic question about a potential project. I am CCing Rik, so that he may be able to provide more insight. This project is pretty difficult as mentioned by Rik already on the page, so you may really want to see if you are even ready to undertake this one. This would require a very good understanding of entire memory management system of Linux Kernel(one of the most difficult things) and understanding of hypervisor apis and virtualization infrastructure in kernel and related software.

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RE: Introducing Myself, Looking to Learn
by Rakesh Ganimineni Sept. 4, 2013

Sept. 4, 2013

I would suggest you to fix on a module and start following what are the bugs in it and see if you can fix it or try understand what others fix. From: Arlie Stephens Sent: 4/9/2013 7:08 To: Varad Gautam Cc: kernelnewbies(a)kernelnewbies.org Subject: Re: Introducing Myself, Looking to Learn Hi Varad, On Sep 04 2013, Varad Gautam wrote: > > Hi! > I want to start working on the Linux kernel but am an absolute > beginner. I am currently on my way through Robert Love's Linux > Kernel Development and need help with finding something I can work > on to get a hang of what it's like. How much of a beginner are you? In particular, how much do you know about operating system kernels in general? And how much multi-threaded programming have you done, in situations where you have to manage your own locking? If you don't have good practical understanding of concurrency, you might want to do yourself a favour and do some work with a large multi-threaded program until you've got practical experience with race conditions, lock contention, and deadlocks. Linux is a fairly mature monster. This means that the simple outlines of what all OSes do tend to be obscured by layers of complexity. That's one some folks use BSD for their OS-kernel classes. You'll be doing more digging in linux. Will you be comfortable with that? > I have also subscribed to the LKML, but find it completely > incomprehensible! My question would be "incomprehensible how?" There's a lot of shared context, which you won't have, and diffs aren't the best way to learn what's in a piece of code. That level of "incomprehensible" makes sense to me. Beyond that, there's learning you need to do. > As a beginner, would it be better to work with the > kernel of a specific OS (I'm running Ubuntu), or work on the > upstream kernel? Pick one that you actually run - that way you're set up to try out the results of your experiments, and more likely to encounter some problem that motivates you to attack it. Personally I'd prefer not to be testing on my development system [hate it when that's unstable], but if you aren't playing with hardware, VMs make great test environments. Beyond that, my advice would be to do something trivial. How about a kernel module that prints "Hello world"? It's useless, but you'll start internalizing the build system. Then do something else trivial, that let's you poke the kernel somewhere else. Eventually either it'll start making sense, and your ambitions will increase - or you'll decide you aren't having fun and try somethign else. -- Arlie (Arlie Stephens arlie(a)worldash.org) _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Being a newbie ;-) (was Re: Introducing Myself, Looking to Learn)
by Arlie Stephens Sept. 4, 2013

Sept. 4, 2013

On Sep 03 2013, Robert P. J. Day wrote: > i'm going to jump in here since i see this question annoyingly > frequently -- "i'm new to the kernel and i want to get involved and > write code; how do i start?" to be blunt, if that's your starting > point, you're not ready to write code for the kernel. period. It seems to me there are a lot of reasons to ask this question, and it's not a great idea for the kernel (in the long run) to discourage newbies to the extent that "new blood" never comes in. > as vladis quite correctly points out, gone are the days when there > was piles of simple coding to be done. most of the kernel is well > established, solid and stable, and ongoing development is *very* > advanced. in other words, there's less and less room for enthusiastic > beginners. but there's more. I think you can expect it will be a while before you write anything that's remotely worth upstreaming, except possibly drivers for obscure hardware or possibly minor bug fixes, for bug(s) that happen to replicate on your own system. That doesn't mean you can't learn. In fact, it's even possible to get paid to learn. At the moment, I'm working in a shop that ships appliances that include linux. My job is to investigate whatever goes squirrely at the kernel level, and make the system play nicely with our latest hardware. Since we're running an older version of linux, the most common result of these investigations is to find and merge an upstream patch. Another common result is to find a bug in one of our own kernel modules. Next most likely is a configuration issue. If none of these apply, we get to write the patch ourselves. If the problem affects recent kernels, we'll also submit it to LKML etc. I haven't personally had cause to submit anything yet. > it's somewhat absurd to say you want to get involved in kernel > development, then ask *others* where you should start. it's like > saying, "i really want to write a book, but i have no idea what i > should write about. can you give me some ideas for a plot? and > characters? and possibly an ending?" yes, it's that silly. I tend to take this as a request for suggestions for learning exercises, or even simply where to start learning. It's a big and complex system, with layers and layers of details to deal with. I doubt "where do I start" is really a variant of "what should I develop?" (The right answer to that is pretty simple - whatever you want to have available, that isn't available ;-)) > > if you're a beginner, then the obvious starting point is to start > reading. and read. and read. and when you're done reading, read some > more. and slowly, you'll figure out what interests you most. and > that's where you then spend your time. Personally, I'd suggest playing with the code. Don't expect to produce something upstreamable. My latest ludicrous activity was reinventing part of "ftrace" ;-) I didn't mean to do that, I was just trying to get a record of [..things ftrace could have gotten me..] on a repeatedly failing system. Net result - I learnt more than I would have if I'd just used ftrace, and my coworkers are being patient about the time it's taking me to solve the original crash. (Fortunately I found a problem with the kernel configuration we were using for that appliance, as a side effect of my experiments, so the effort wasn't completely wasted ;-) And now I know about ftrace, and have ideas about extending it to do the next batch of things I want.) > > rday > -- Arlie (Arlie Stephens arlie(a)worldash.org)

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Introducing Myself, Looking to Learn
by Varad Gautam Sept. 3, 2013

Sept. 3, 2013

Hi! I want to start working on the Linux kernel but am an absolute beginner. I am currently on my way through Robert Love's Linux Kernel Development and need help with finding something I can work on to get a hang of what it's like. I have also subscribed to the LKML, but find it completely incomprehensible! As a beginner, would it be better to work with the kernel of a specific OS (I'm running Ubuntu), or work on the upstream kernel? Thanks. Varad

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Need help for getting started
by 901stt＠gmail.com Sept. 3, 2013

Sept. 3, 2013

Hello all, I am a newbie here. I'd like to contribute in architectures, kernel features, virtualization, and drivers parts, but I don't know where is a good way to start. I have looked for some advice but I have had a hard time to understand (Some advice is too general. Some used too old kernel versions, so I cannot catch up when reading the newer ones). I learned about OS, C language, and assembly language. I can configure and build the kernel. Would someone guide me where should I start? I appreciate for your helping. Sorry if there are some errors in my writing, because English is not my native language.

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Info Virtual Rootkit Blocker
by Shubhashish Behera Sept. 2, 2013

Sept. 2, 2013

Please provide me some info about virtual Rootkit blocker. Thanks n Regards Shubhashish Behera MCA, Utkal University Cell: - +919040313013 Mail to: shubhashish_001(a)yahoo.co.in

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SPI Slave Mode Driver
by techi eth Sept. 2, 2013

Sept. 2, 2013

Hi All, Is Linux kernel support high speed SPI slave mode driver ? I have one board (SPI Master ) which is connected by linux supported board on spi (SPI slave). If anybody tested on the same then please provide some hint on performance. Cheers - Techi

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