February 2011 - kernelnewbies@kernelnewbies.org

How to free data block of ext2 fs?
by kashish bhatia Feb. 16, 2011

Feb. 16, 2011

Hi all , I wanted to free a data block from disk. So I made a loop device for ext2 fs and inserted my module(code) through insmod command. Here are the details : I found a function named ext2_free_data() which takes block numbers to be freed as a parameter. The declaration of the function is as follows : void ext2_free_data(struct inode *inode, __le32 *p, __le32 *q); As we can see this function use structure of inode object and it make changes in this inode object. This function changes the fields in in-core inode and mark the inode dirty. But I want the changes made in in-core inode to be reflected in disk inode immediately . Is there any command to flush the buffers ? -- Regards, Kashish

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Re: Mapping memory between kernel and user space
by Sri Ram Vemulpali Feb. 16, 2011

Feb. 16, 2011

As was suggested I started reading chap 15v from LDD. I ran more into confusion state. I know that virtual address(process space), linear address (segmentation) and physical address. And how are they resolved from virtual to physical. But coming to kernel they distinguish logical address from virtual address. What is the main difference. Also, they emphasize on high memory and low memory. Why can not high memory can be mapped in to kernel completely. Why is that kernel has less visibility of complete space available on RAM. Linux MM is it a very specific implementation of linux, or Is that a traditional implementation. what is very minimal implementation of MMU for real time systems. Thanks in advance. --Sri. On Tue, Feb 15, 2011 at 12:54 AM, Ankita Garg <ankita(a)in.ibm.com> wrote: > On Wed, Feb 09, 2011 at 06:45:42PM -0500, Sri Ram Vemulpali wrote: >> Hi all, >> >> How do I map some space between kernel and user space. Can anyone >> point me in to right direction. I was trying to map the packets from >> my netfilter function to kernel user space, to avoid over head of >> copying. Thanks in advance. >> > > You can take a look at remap_pfn_range() routine when implementing mmap > in your driver. > > -- > Regards, > Ankita Garg (ankita(a)in.ibm.com) > Linux Technology Center > IBM India Systems & Technology Labs, > Bangalore, India > -- Regards, Sri.

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multicore and crash
by naveen yadav Feb. 16, 2011

Feb. 16, 2011

Hi All, I need small clarification for multicore linux kernel Case;1 Kernel space: 1. If on two CPU's both running in kernel space and both crash at same time t. what will happen will we get two crash dumps of registers or single ? Case :2 User Space: 1. If on two CPU's both running in User space and both crash at same time t. what will happen will we get two core files, Single core with dump for both ? Thanks

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task_struct related query
by mohit verma Feb. 16, 2011

Feb. 16, 2011

hi all , when a process executes a function , is there any way by which i can figure out the reference to that function or any footprint of that function via task_struct (current)? -- ........................ *MOHIT VERMA*

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Interrupt handling
by Darshan Ghumare Feb. 16, 2011

Feb. 16, 2011

---------- Forwarded message ---------- From: Darshan Ghumare <darshan.ghumare(a)gmail.com> Date: Wed, Feb 16, 2011 at 10:14 AM Subject: Re: Interrupt handling To: Mulyadi Santosa <mulyadi.santosa(a)gmail.com> Sir, > > On Tue, Feb 15, 2011 at 4:16 PM, Mulyadi Santosa < > mulyadi.santosa(a)gmail.com> wrote: > >> Hi... :) >> >> On Tue, Feb 15, 2011 at 16:08, Darshan Ghumare >> <darshan.ghumare(a)gmail.com> wrote: >> > Sir, >> > On x86 UP (Single CPU), Can lower priority (say) IRQ5 preempt higher one >> > (say) IRQ4 (Currently, CPU is executing interrupt handler of IRQ4)? >> >> In Linux kernel, I never heard such irq prioritizing. Linux kernel >> does general preemption such that any code path could preempt other >> code path as long as preemption is allowed at that point and/or >> interrupt is enabled (which one affect the situation depends on type >> of code path). >> > > IMHO, When the Processor is executing interrupt handler of IRQ4 then > Processor is the one which pushes SS, SP, EFLAGS, CS & EIP on stack (in > this case this will all corresponds to interrupt handler of IRQ4) & loads CS > & EIP corresponding to IRQ5. > So, how come its depends on OS (kernel)? Please correct me if I am wrong. > > >> But, vaguely I read that Windows kernel does that.... that's why in >> certain BSOD you read message prefixed with "IRQL xxx xxx xxxx". That >> means lower interrupt handler somehow preempt higher one and that's >> not allowed. >> >> It comes from my raw observation so things might be wrong somewhere... >> >> -- >> regards, >> >> Mulyadi Santosa >> Freelance Linux trainer and consultant >> >> blog: the-hydra.blogspot.com >> training: mulyaditraining.blogspot.com >> > -- Darshan®

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Page Cache Address Space Concept
by piyush moghe Feb. 15, 2011

Feb. 15, 2011

While going through Page Cache explanation in "Professional Linux Kernel" book I came across one term called "address space" ( not related to virtual or physical address space ) I did not get what is the meaning of this address space, following is verbatim description: "To manage the various target objects that can be processed and cached in whole pages, the kernel uses an abstraction of the "address space" that associates the pages in memory with a specific block device (or any other system unit or part of a system unit). This type of address space must not be confused with the virtual and physical address spaces provided by the system or processor. It is a separate abstraction of the Linux kernel that unfortunately bears the same name. Initially, we are interested in only one aspect. Each address space has a "host" from which it obtains its data. In most cases, these are inodes that represent just one file.[2] Because all existing inodes are linked with their superblock (as discussed in Chapter 8), all the kernel need do is scan a list of all superblocks and follow their associated inodes to obtain a list of cached pages" Can anyone please explain what is the use of this and what this is all about? Regards, Piyush

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directory entry
by mohit verma Feb. 15, 2011

Feb. 15, 2011

hi all, is there any way to find out the offset or the directory entry number of a file in the directory ? let me explain a bit more: when we open a drectory via open(2) and find out the directory entry by readdir(2,3) or getdents(2) it automatically increases to the next directory entry and fills in the dirent structure. but in kernel space , let we have the parent directory name and child of it . so is there any way to figure out at what offset or what number (exactly) that perticular child will occur in the directory contains? -- ........................ *MOHIT VERMA*

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The difference between sk_err_soft and sk_err
by Simon Liu Feb. 15, 2011

Feb. 15, 2011

Hi all. I read kernel's source, there is sk_err_soft and sk_err in struct sock. this is their comment: * @sk_err: last error * @sk_err_soft: errors that don't cause failure but are the cause of a * persistent failure not just 'timed out' this make me confuse, why need sk_err_soft? I search linux kernel tree, and find use sk_err_soft in ICMP module. after that in man 2 connect : EINPROGRESS The socket is nonblocking and the connection cannot be completed immediately. It is possible to select(2) or poll(2) for completion by selecting the socket for writing. After select(2) indicates writability, use getsockopt(2) to read the SO_ERROR option at level SOL_SOCKET to determine whether connect() completed successfully (SO_ERROR is zero) or unsuccessfully (SO_ERROR is one of the usual error codes listed here, explaining the reason for the failure). i know SO_ERROR will detect sk_err_soft and sk_err, further more there is not detect sk_err_soft in tcp_poll. my question is why not return EPOLLERR in tcp_poll( detect sk_err_soft). Thank! -- 博观约取豆瓣:www.douban.com/people/mustang/ blog: www.pagefault.info twitter: www.twitter.com/minibobo

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Re: Transient Delivery Failure
by kashish bhatia Feb. 11, 2011

Feb. 11, 2011

> > Hi Dave, > Yes, I know which symbol is unknown in my module. It is ext2_free_data() function. I think the function is not exporting properly. The entire detail of my doubt is present in first thread of this mail. -- Regards, Kashish

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Mapping memory between kernel and user space
by Sri Ram Vemulpali Feb. 11, 2011

Feb. 11, 2011

Hi all, How do I map some space between kernel and user space. Can anyone point me in to right direction. I was trying to map the packets from my netfilter function to kernel user space, to avoid over head of copying. Thanks in advance. -- Regards, Sri.

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