May 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

should failed calls to device_register() always call put_device()?
by Robert P. J. Day May 29, 2011

May 29, 2011

from drivers/base/core.c, we have the fairly unambiguous advice: * NOTE: _Never_ directly free @dev after calling this function, even * if it returned an error! Always use put_device() to give up the * reference initialized in this function instead. */ int device_register(struct device *dev) { device_initialize(dev); return device_add(dev); } and yet, there appears to be driver code that does exactly that, such as this snippet from drivers/w1/w1_int.c (line 86): ... snip ... err = device_register(&dev->dev); if (err) { printk(KERN_ERR "Failed to register master device. err=%d\n", err); memset(dev, 0, sizeof(struct w1_master)); kfree(dev); dev = NULL; } return dev; isn't the above doing just that -- directly freeing the dev structure without first calling put_device()? or am i misreading something? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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Can we map a device address to two different memory locations?
by sandeep kumar May 28, 2011

May 28, 2011

Hi all, Memory mapping is done so that CPU can access the devices, which it cant unless. Now the question is can we memory map a one device resource(say some iomemory) to two different memory locations? the other way of seeing at this question is, Will ioremap() gives different 'virtual addresses' when called multiple times? Please give reply.. -- With regards, Sandeep Kumar Anantapalli,

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Re: How to use the cryptographic API (e.g. md5 checksum)?
by Arvid Brodin May 28, 2011

May 28, 2011

Peter Teoh wrote: > On Tue, May 24, 2011 at 6:43 AM, Arvid Brodin <arvid.brodin(a)enea.com> wrote: >> Hi, >> >> I want to perform an md5 checksum on a process' text segment (I create a file >> /proc/<pid>/text_checksum that, when read, should give the md5sum). >> >> The crypto api documentation (Documentation/crypto/api-intro.txt) seems to be >> quite lacking. The only example is: >> >> tfm = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC); >> if (IS_ERR(tfm)) >> fail(); >> >> /* ... set up the scatterlists ... */ >> >> desc.tfm = tfm; >> desc.flags = 0; >> >> if (crypto_hash_digest(&desc, sg, 2, result)) >> fail(); >> >> crypto_free_hash(tfm); >> >> Looking at some existing code, I see usage of crypto_hash_init(), >> crypto_hash_final(), desc.flag set to CRYPTO_TFM_REQ_MAY_SLEEP, >> ... (e.g. in fs/ecryptfs/crypto.c). Does anybody know what they do? Do I need > > http://www.redhat.com/archives/dm-devel/2005-August/msg00058.html Thanks, that explains the CRYPTO_TFM_REQ_MAY_SLEEP flag! >> to, or should I, use them? The functions are are declared in include/linux/crypto.h >> as some kind of wrapper functions, but lack documentation. Also, Google has not >> been my friend here. > > http://www.linuxjournal.com/article/6451?page=0,0 This link is one I've found before, and it really does not explain anything about the usage of crypto_hash_{digest,init,update,final}() as far as I can see. So I'm still looking for help on this! Thanks, Arvid Brodin Enea Services Stockholm AB

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How a program could generate the memory addresses for its variables, when it is about to run?
by sandeep kumar May 27, 2011

May 27, 2011

hi all, I am new to the linux kernel internals. I know there is a memory management subsystem which handles all the memory related things. But Now i want to know a bit deeper how things work. I want to start with the following question, *How a program could generate the memory addresses for its variables, when it is about to run?* ** Can please somebody give pointers how to learn this kind of things like, "in the early stages (when our program is about to be executed..about to become a process) what are the things that will be done by the kernel?" Please help me in this regard, Thanking you, Sandeep Kumar A.

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Questions about preemption and concurrency
by Naman shekhar Mishra May 27, 2011

May 27, 2011

In Operating System Concepts 6th ed, chapter 20: "Kernel code can thus assume that it will never be preempted by another process and that no special care must be taken to protect critical sections. The only requirement is that critical sections do not contain references to user memory or waits for I/O completions" Why us that the process cannot wait for I/O to complete in critical sections? My another question is: While developing kernel modules (for kernels before 2.6), do we need to keep concurrency in mind? Because the modules run as part of the kernel and no two processes can run in the kernel at the same time? Or my question is wrong since they CAN run in the kernel at the same time (like when one process waits for I/O completion and another is scheduled to run which then makes a system call)? Please excuse me for the multiple nested question since I didn't quite know how to put it.

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How to limit the total size used by core files or automatically delete old corefiles.
by SADA SIVA REDDY S May 27, 2011

May 27, 2011

Hi All, I have a situation like below. I am using RHEL 5. 1. I have multiple user processes running on my machine. 2. I have set the appropriate sizes for core file size. 3. But my process maangement demon is designed to restart any process that terminates. 4. Hence the process starts up again. 5. If I have a very bad nasty defect, it will keep on filling my machine with core files until I run out of space on the partition. My Questions: 1. Is there a provision in Linux to automatically cleanup the old corefiles when we reach a certain limit ? 2. Is there a provision in Linux to set a upper limit for space occupied by all core files (not individual core files) ? Any inputs appreciated. Thanks, SADA

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Struct Inheritance in drivers/ata/
by Peter Hamilton May 27, 2011

May 27, 2011

The code in drivers/ata/ uses an implementation of inheritance that I have not seen before. It's only briefly explained in the header file ( include/linux/libata.h:885): /* * ->inherits must be the last field and all the preceding * fields must be pointers. */ The structs are then initialized with .inherits assigned first: drivers/ata/sata_nv.c:475 static struct ata_port_operations nv_nf2_ops = { .inherits = &nv_generic_ops, .freeze = nv_nf2_freeze, .thaw = nv_nf2_thaw, }; Is this actually implementing inheritance? Why do all preceding fields need to be pointers? As far as I can tell, this style is only found in the ata drivers. Could anyone explain how this works? Thanks, Peter

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kernel BUG at kernel/workqueue
by sri May 27, 2011

May 27, 2011

Hi, Am trying to learn network drivers in linux. I need help in understanding the following error and what various information we can get from that, so that I can identify the problem. >From the backtrace, it is clear that the e1000_watchdog is throwing the error. This error I have seen on Centos 5.5 (kernel-2.6.18-194) and whenever am doing ifconfig up or ifconfig down, this is shown. kernel BUG at kernel/workqueue.c:113! invalid opcode: 0000 [#1] SMP last sysfs file: /class/net/eth1/address Modules linked in: proclikefs(U) deflate(U) zlib_deflate(U) af_key(U) autofs4(U) kick(U) dm_mirror(U) dm_log(U) dm_multipath(U) scsi_dh(U) dm_mod(U) parport_pc( U) lp(U) parport(U) sg(U) snd_intel8x0(U) snd_ac97_codec(U) ac97_bus(U) snd_seq_ dummy(U) snd_seq_oss(U) snd_seq_midi_event(U) snd_seq(U) snd_seq_device(U) snd_p cm_oss(U) snd_mixer_oss(U) snd_pcm(U) snd_timer(U) snd(U) soundcore(U) snd_page_ alloc(U) e752x_edac(U) edac_mc(U) ehci_hcd(U) i6300esb(U) pcspkr(U) uhci_hcd(U) ata_piix(U) libata(U) sd_mod(U) scsi_mod(U) ext3(U) jbd(U) CPU: 0 EIP: 0060:[<c043196a>] Tainted: G VLI EFLAGS: 00010207 (2.6.18-194.el5 #1) EIP is at queue_work+0x32/0x50 eax: dfdad470 ebx: 00000000 ecx: dfee7300 edx: dfdad46c esi: 00000000 edi: dfdad000 ebp: 00000100 esp: de50fecc ds: 007b es: 007b ss: 0068 Process ifup-eth (pid: 14665, ti=de50e000 task=d9030550 task.ti=de50e000) Stack: dfdad400 dfdad614 c05628bf dfdad50c de50ff44 de50fefc c076a000 dfdad418 00000100 c042bf99 dfdad400 c05623af de50fefc de50fefc 00000046 00000021 c0705308 0000000a c04286e0 00000000 00000046 de50ff44 d9030550 00000007 Call Trace: [<c05628bf>] e1000_watchdog+0x510/0x56a [<c042bf99>] run_timer_softirq+0x14d/0x1d0 [<c05623af>] e1000_watchdog+0x0/0x56a [<c04286e0>] __do_softirq+0x87/0x114 [<c04287a3>] do_softirq+0x36/0x3a [<c0406255>] do_IRQ+0x48/0x53 [<c0404896>] common_interrupt+0x1a/0x20 [<c042007b>] __build_sched_domains+0x87a/0xaa4 [<c0460cdb>] find_vma+0x30/0x51 [<c062ce4e>] do_page_fault+0x1b2/0x52d [<c042c800>] sigprocmask+0xb0/0xce [<c062cc9c>] do_page_fault+0x0/0x52d [<c04049b5>] error_code+0x39/0x40 ======================= Code: 00 e0 ff ff 8b 70 10 90 0f ba 2a 00 19 c0 31 db 85 c0 75 30 8b 1d f4 b8 76 c0 8d 41 08 39 41 08 8d 42 04 0f 45 de 39 42 04 74 08 <0f> 0b 71 00 35 38 65 c0 8b 01 f7 d0 8b 04 98 bb 01 00 00 00 e8 EIP: [<c043196a>] queue_work+0x32/0x50 SS:ESP 0068:de50fecc <0>Kernel panic - not syncing: Fatal exception in interrupt <0>Rebooting in 60 seconds.. -- -- Krishna Mohan B

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Identifying the type of the kernel routine executing in the kernel at a particular time instant
by limp May 26, 2011

May 26, 2011

Hi all, I know that kernel routines can be activated in several ways and many different things can be executed in the kernel: . A process invokes a system call (a system call is executed in the kernel). . The CPU executing a process, signals an exception (e.g. due to an invalid instruction). In this case, an exception handler is executed under the kernel on behalf of the process that caused it. . A peripheral device issues an interrupt signal to the CPU and the kernel executes the corresponding interrupt handler. . A kernel thread is executed in the kernel. What I want to do is to find a way of identifying what is currently executed under the kernel by either looking the values of CPU registers (I am talking about the x86 architecture) or by looking at particular flags or values being set in various Linux structures (such as the task_struct). In particular, I want to know if a kernel thread, an interrupt handler, an exception handler, etc is executed at a particular time instant in the kernel. For example, is there a way to tell that a system call is executed (and ideally, which one)? Would the execution of a system call set a particular value to a CPU register or to the task_struct of the process of which is executed under? Regarding the peripheral interrupt case, I guess we can tell if an interrupt handler is executed by looking at the ISR flags of the used by Linux interrupt controller(s). What I would like is to find out similar tricks for identifying any other possible kernel routines that could be executed (e.g. system call, exception handler, etc.). Any help will be much appreciated. Kind regards, John K.

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Rv: Re: knewbies project? - updating LDD3 source
by Ezequiel García May 26, 2011

May 26, 2011

> > De: DG <dangets(a)gmail.com> > > Asunto: Re: knewbies project? - updating LDD3 source > > Para: "Jim Cromie" <jim.cromie(a)gmail.com> > > Cc: "kernelnewbies" <kernelnewbies(a)kernelnewbies.org> > > Fecha: martes, 24 de mayo de 2011, 15:14 > > On Tue, May 24, 2011 at 11:47 AM, > > Robert P. J. Day > > <rpjday(a)crashcourse.ca> > > wrote: > > > On Tue, 24 May 2011, Jim Cromie wrote: > > > > > >> over at http://code.google.com/p/ldd3/ > > >> it says: > > >> The famous "Linux Device Drivers" released > the > > sample code. but the > > >> code does not reflect the latest kernel > updates, > > some of code cannot > > >> even compile. This project is to make it > > compatible with the current > > >> kernel. > > >> > > >> http://lwn.net/Kernel/LDD3/ > > >> http://examples.oreilly.com/9780596005900/ > > > > > > the one caution i would give here is that quite > a > > bit of code in > > > LDD3 shouldn't be updated, anyway, since it > reflects > > features that > > > have been deprecated for quite some time. > > > > > > for instance, no one should be writing proc > files > > anymore. also, > > > ioctl()s are also discouraged for the most part. > so > > i would be > > > selective about what parts of LDD3 code *should* > be > > updated as > > > examples of good kernel programming. > > > > > > rday > > > > There is a repo on GitHub with the same purpose. I > > haven't checked it > > out personally, but it's probably worth a look. > > > > https://github.com/martinezjavier/ldd3 > > I've found the same googlecode svn repo a while ago, but > since it was very out-dated, I decided to start my own > project on github. > > https://github.com/ezequielgarcia/ldd3-examples > > I am working against 2.6.37; but currently, the only module > that really compiles is scull and scullpipe. martinezjavier > git repo seems much updated; too bad I haven't find that > when I looked for ! > > Maybe we should concentrate our efforts, despite for me it > was just a learning project. > > Greetings, > Ezequiel. > > >

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