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some questions about block and scatterlist
by loody Nov. 1, 2011

Nov. 1, 2011

Dear all: My questions are below: 1. Are all struct page 32-bit aligned? If so, where is this part of code for handleing struct page be 32-bits aligned? 2. if the page of scatterlist is located at high mem, how does dma_map_sg mapping the virtual address? 3. in blk_rq_map_sg, it seems we only copy bvec->bv_page to sg->page_link why don't we add dma_address in bvec and send the bio directly to the lower level driver? 4. if I plug a USB HD with 3 partitions, will there be 3 request_queues? -- Regards,

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seagate drive and i/o errors
by Littlefield, Tyler Nov. 1, 2011

Nov. 1, 2011

Hello all, I have a quick question. When I do a ls on this drive and it's spun down, i get an i/o error. I'm curious if there's a way to write a module or do something to make the drive wake up when I do a r/w request on it? I've had an external and it never had this problem. I also know i could modify the scsi params to make it not sleep, but that doesn't work and that is not the best of ideas anyway. I like it sleeping, I don't even mind waiting for an LS. It's just hard to manage when i have to umount -l the directory, then figure out what sd* dev it's on. -- Take care, Ty Web: http://tds-solutions.net The Aspen project: a light-weight barebones mud engine http://code.google.com/p/aspenmud Sent from my toaster.

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generic I/O
by Kai Meyer Oct. 31, 2011

Oct. 31, 2011

Are there existing generic block device I/O operations available already? I am familiar with constructing and submitting 'struct bio's, but what I'd like to do would be greatly simplified if there was an existing I/O interface similar to the posix 'read' and 'write' functions. If they don't exist, I would probably end up writing functions like: int blk_read(struct block_device *bdev, void *buffer, off_t length); int blk_write(struct block_device *bdev, void *buffer, off_t length); Pros and cons to this sort of approach? -Kai Meyer

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ext4 extents
by Mike Gibson Oct. 30, 2011

Oct. 30, 2011

I'm updating a user space program that finds free blocks on a ext2/3 filesystem so that it works with ext4. I'm concerned about how extents might affect my program. My program currently looks only at the block allocation bitmaps. Are the block allocation bitmaps still updated when an extent is created? >From what I can tell, extent information is only stored in the inode, and is only a way to improve the efficiency of the process of creating the structure needed in the inode. But I haven't been able to find out anything about whether the block allocation bitmap is updated at the same time. Do extents provide a new way of expressing which blocks are allocated on disk? Or are the block allocation bitmaps still the canonical way to determine if a given block is in use? Mike Gibson

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[ANNOUNCE] Xvisor: eXtensible Versatile hypervISOR
by Chauhan, Himanshu Oct. 28, 2011

Oct. 28, 2011

We are pleased to announcing Xvisor v0.1.0, a new open source bare-metal hypervisor, which aims towards providing virtualization solution, which is light-weight, portable, and flexible with small memory foot print and less virtualization overhead. It is distributed under GNU Public License (GPLv2). Xvisor has most of the features expected from a modern full fledged hypervisor: - Tree based configuration - Tickless and high resolution timekeeping - Threading framework - Device driver framework - CPU virtualization - Address Space virtualization - Device emulation framework - Serial port virtualization - Managment terminal Xvisor is currently being ported for two architectures: ARM and MIPS. The development & testing is being done using QEMU (0.14.xx or higher). Xvisor ARM is able to boot multiple unmodified Linux-2.6.30.10 or Linux-3.0.4 guest with a fairly interactive and smooth Busybox 0.19.2 console. Currently supported host for Xvisor ARM is Realview-PB-A8 Board emulated by QEMU. It is also being ported to real hardware, specifically Beagle Board. Please try out our Xivsor ARM demo on QEMU (0.14.xx or higher). To download the demo tarball visit the link below: https://docs.google.com/a/brainfault.org/leaf?id=0B0ABS_s60oP_OGE2MDA0MWYtN… Xvisor MIPS is still a work in progress and will be announced very soon. Xvisor is currently hosted on Github, to clone or download source code please visit following links: Mainline: https://github.com/xvisor/xvisor ARM Development: https://github.com/avpatel/xvisor-arm MIPS Development: https://github.com/hschauhan/xvisor-mips Our developer mailing list is xvisor-devel[at]googlegroups[dot]com, please feel free to post your queries or join our development mailing list.

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Kernel Module from C program
by Luis Morales Oct. 27, 2011

Oct. 27, 2011

Greetings, I'm new to the world of kernel modules programming. I've read the Linux Kernel Module Programming Guide by Peter Jay Salzman, among other documents, and I have the following question: I'd like to know if it's possible to take a program developed in C (in this case OpenSIPs, which is a SIP Proxy Server) and turn it into a kernel module (I know "to turn it" is probably not the right expression, what I mean is if I could modify it somehow so that it can be loaded as a kernel module) ? As far as I've understand, kernel modules are developed for drivers or to do some modifications to system calls, but I like to know if it's possible to do what I stated earlier. Thanks, Luis Morales.

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Question on Memory Leak: very tough problem
by Sri Ram Vemulpali Oct. 27, 2011

Oct. 27, 2011

Hi All, I have very difficult problem I am working on to figure out where the memory leak is in my system. Sometimes it shows up and sometimes it reveals very slowly (I mean increments very slowly). This is dependent on system load, if the system is in very high load, then leak is very fast. We tried solving this problem from many dimensions, but no success. After quite sometime, we started using valgrind to capture the memory leak. The funny thing is the leak disappears once we start running our application on top of valgrind. So, we cannot capture leak using valgrind. We came to conclusion that, since valgrind serializes the allocations (leak disappears), we thought this might be result of race conditions, that resulted from system high load (by the way ours is multi threaded system). We run system without valgrind we see the memory leak. The question is, is it true that valgrind serializes the mem allocations. Does this happen to anyone disappearing the leak when used valgrind. Any thoughts and input that can help me solve this problem. Thanks to all in advance. -- Regards, Sri.

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how to check kernel is configured with preemption or not
by sri Oct. 27, 2011

Oct. 27, 2011

Hi, Am using kernel 2.6.18-195(centos 5.5). My kernel configs have CONFIG_PREEMPT_NONE=7 and "CONFIG_PREEMPT_VOLUNTERY is not set". How to check that preemption is really in place? Is there any way to check my kernel is configured with what preemption levels? Thanks inadvance. -- Sri -- -- Krishna Mohan B

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Workqueue and kernel panic on device disconnect
by Frank Schäfer Oct. 26, 2011

Oct. 26, 2011

Hi, I'm trying to use a workqueue in a usb driver for polling the states of the device buttons. That works fine, but when I disconnect the device, the kernel sometimes explodes. The machine turns off immediately, without saving a backtrace (I will try to make a photo tomorrow) The code: static struct delayed_work poll_work; static const struct usb_device_id device_table[] = { {USB_DEVICE(0x1234, 0x5678)}, {} }; static void poll(struct work_struct *work) { schedule_delayed_work(&poll_work, msecs_to_jiffies(100)); } MODULE_DEVICE_TABLE(usb, device_table); static int test_probe(struct usb_interface *intf, const struct usb_device_id *id) { INIT_DELAYED_WORK(&poll_work, poll); schedule_delayed_work(&poll_work, msecs_to_jiffies(100)); return 0; } static void test_disconnect(struct usb_interface *intf) { cancel_delayed_work_sync(&poll_work); } static struct usb_driver test_driver = { .name = MODULE_NAME, .id_table = device_table, .probe = test_probe, .disconnect = test_disconnect, }; static int __init test_mod_init(void) { return usb_register(&test_driver); } static void __exit test_mod_exit(void) { usb_deregister(&test_driver); } module_init(test_mod_init); module_exit(test_mod_exit); What am I doing wrong ? Is there anything else I have to do in addition to calling cancel_delayed_work_sync() in the disconnect fcn ? Thanks, Frank Schaefer

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Fix procmail rule in ML wikipage
by chandanrmail＠gmail.com Oct. 25, 2011

Oct. 25, 2011

The procmail rule for "netdev:Linux network development list" has a typo. The "condition" should be as shown below: * ^X-Mailing-List:.*netdev@vger\.kernel\.org Regards, chandan r

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