November 2011 - kernelnewbies@kernelnewbies.org

What's the meaning of PREEMPT_ACTIVE in preempt_count?
by Parmenides Nov. 7, 2011

Nov. 7, 2011

Hi, The preempt_count contains a PREEMPT_ACTIVE flag. In cond_resched() and preempt_schedule(), there is a pattern which is like this: add_preempt_count(PREEMPT_ACTIVE); schedule(); sub_preempt_count(PREEMPT_ACTIVE); I wonder what's the role which PREEMPT_ACTIVE plays. Why we need to add to it before schedule() and sub from it after?

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Re: Problem in configuring the kernel
by Naman Shekhar Mishra Nov. 6, 2011

Nov. 6, 2011

On Sun, Nov 6, 2011 at 10:13 PM, Naman Shekhar Mishra < mishra123.naman(a)gmail.com> wrote: > > > On Sun, Nov 6, 2011 at 10:10 PM, Greg KH <greg(a)kroah.com> wrote: > >> On Sun, Nov 06, 2011 at 10:00:44PM +0530, Naman Shekhar Mishra wrote: >> >> <snip> >> >> For some reason you sent this only to me, which is a bit rude to >> everyone else on the mailing list. I'll be glad to respond if you >> resend it to everyone. >> >> thanks, >> >> greg k-h >> > > I am really sorry, I am new to this mailing list :). I will keep it in > mind... but can you please help me out here. I am really trying to get this > thing working > >

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Problem in configuring the kernel
by Naman Shekhar Mishra Nov. 6, 2011

Nov. 6, 2011

I have been trying to configure the kernel for my Lenovo 300 N100 machine. First I tried to use: $make defconfig but this doesn't work and there is a kernel panic when I boot with the new kernel. Then I used the configuration file that came with the Ubuntu distribution and it ran just fine, but the problem is that it takes TOO long to compile with that configuration. What I want is a minimum configuration which runs the hardware on my machine. I looked up "Linux Kernel in a Nutshell" and ran a script which looks through the hardware and shows only the modules I want to be using #!/bin/bash # # find_all_modules.sh # for i in `find /sys/ -name modalias -exec cat {} \;`; do /sbin/modprobe --config /dev/null --show-depends $i ; done | rev | cut -f 1 -d '/' | rev | sort -u I have attached the output of the script if anyone wants to check what modules it showed. So I once again started the configuration: $make defconfig to get a base configuration and then enabled[m] the configuration option for each module as demonstrated in the book. But, for some modules there was no configuration option. And for the rest, the option was already enabled by defconfig. When I booted with this new kernel, the kernel panicked. Please tell me how to make the kernel work for my particular machine. Regards

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How to refer to the unamed structure in page struct
by Jimmy Pan Nov. 4, 2011

Nov. 4, 2011

truct page { unsigned long flags; /* Atomic flags, some possibly * updated asynchronously */ atomic_t _count; /* Usage count, see below. */ union { atomic_t _mapcount; /* Count of ptes mapped in mms, * to show when page is mapped * & limit reverse map searches. */ struct { /* SLUB */ u16 inuse; u16 objects; }; }; union { struct { unsigned long private; /* Mapping-private opaque data: * usually used for buffer_heads * if PagePrivate set; used for * swp_entry_t if PageSwapCache; * indicates order in the buddy * system if PG_buddy is set. */ struct address_space *mapping; /* If low bit clear, points to * inode address_space, or NULL. * If page mapped as anonymous * memory, low bit is set, and * it points to anon_vma object: * see PAGE_MAPPING_ANON below. */ }; #if USE_SPLIT_PTLOCKS spinlock_t ptl; #endif struct kmem_cache *slab; /* SLUB: Pointer to slab */ struct page *first_page; /* Compound tail pages */ }; ------------------------------------------------------------------------- As you can see in the code， the union in the page structure doesn't have a name, so does the structure in the union, how to refer to those two? Thanks in advance, Jimmy

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The meaning of acronym of PIO in kernel?
by loody Nov. 4, 2011

Nov. 4, 2011

Hi all: I found except DMA transfer, there is a mode called PIO. Where I can find the document of this and what is full name of it? -- Regards,

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spin_lock behavior
by Prajosh Premdas Nov. 4, 2011

Nov. 4, 2011

Hi I wrote a sample module which looked like this and i expected the module to hang as i have used 2 spin_lock simultaneously. But i find the print after the second spin_lock being printed and the module works perfectly fine. Can any body please help me in understanding this? I got this problem from a driver i wrote and had a typo "spin_lock" instead of "spin_unlock" the driver worked fine and i caught the mistake only during a review *#include <linux/module.h>* *#include <linux/spinlock.h>* * * *struct sp_q {* *spinlock_t spinlock;* *uint8_t data;* *};* * * *static int __init sp_lck_init(void)* *{* * * * struct sp_q test;* * * * /* Spin lock Init */* * * * spin_lock_init(&test.spinlock);* * * * printk("<1>Test start\n");* * * * spin_lock(&test.spinlock);* * test.data = 0; * * spin_lock(&test.spinlock); * * * * printk("<1>How come???\n");* * return 0;* * * *}* * * *static void __exit sp_lck_exit(void)* *{* * * *}* * * *module_init(sp_lck_init);* *module_exit(sp_lck_exit);* *MODULE_LICENSE("GPL");* -- Regards, Prajosh Premdas

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when and how Notifier Chains calling?
by vichy Nov. 4, 2011

Nov. 4, 2011

hi all: if I register a user-defined notification chain as below: blocking_notifier_chain_register(&my_noti_chain, &my_notifier); under what circumstances it will be called? Regards,

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Question on CDROM access
by sahlot arvind Nov. 4, 2011

Nov. 4, 2011

Hi, I am running Ubuntu 11.10 and my CDROM drive's LED keeps blinking. I want to know which process is accessing CDROM for no reasons. There is no media in the drive, I believe OS seems to access it for media change events, but I am more interested in which process or deamon is actually doing it. I tried the followings and nothing gave anything: 'lsof | grep -in 'cdrom' 'lsof | grep -in 'sr0' 'lsof | grep -in 'sg0' What tools could I use to track down the process, which is accessing my CD drive? Thanks in advance. Asahlot

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spin_lock behavior
by Prajosh Premdas Nov. 2, 2011

Nov. 2, 2011

Hi I wrote a sample module which looked like this and i expected the module to hang as i have used 2 spin_lock simultaneously. But i find the print after the second spin_lock being printed and the module works perfectly fine. Can any body please help me in understanding this? I got this problem from a driver i wrote and had a typo "spin_lock" instead of "spin_unlock" the driver worked fine and i caught the mistake only during a review *#include <linux/module.h>* *#include <linux/spinlock.h>* * * *struct sp_q {* *spinlock_t spinlock;* *uint8_t data;* *};* * * *static int __init sp_lck_init(void)* *{* * * * struct sp_q test;* * * * /* Spin lock Init */* * * * spin_lock_init(&test.spinlock);* * * * printk("<1>Test start\n");* * * * spin_lock(&test.spinlock);* * test.data = 0; * * spin_lock(&test.spinlock); * * * * printk("<1>How come???\n");* * return 0;* * * *}* * * *static void __exit sp_lck_exit(void)* *{* * * *}* * * *module_init(sp_lck_init);* *module_exit(sp_lck_exit);* *MODULE_LICENSE("GPL");* -- Regards, Prajosh Premdas

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Re: ext4 extents
by piyush moghe Nov. 1, 2011

Nov. 1, 2011

Hi Mike, > > 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? > > >> AFAIK block allocations bitmaps are sufficient to give you information > related to block allocations, inode with extents should not > >> make any difference because extents are just to make block reading > efficient and can be used to represent a much bigger FS. > > >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. > > >> As part of extent inode allocation block bitmaps are updated for eg. > you can refer to > >> ext4_map_blocks > >> ext4_ext_map_blocks ( Only called if inode has extents ) > >> ext4_free_blocks > >> ext4_read_block_bitmap > > Regards, > Piyush > > On Sat, Oct 29, 2011 at 3:33 AM, Mike Gibson <mike.gibson(a)storagecraft.com > > wrote: > >> 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 >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > >

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