O_direct Write Error
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Linux O_direct
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Error: ‘o_direct’ Undeclared (first Use In This Function)
working up vote 2 down vote favorite 1 Board Introduction: I am working on a board that has ST40 chip on it basically used for capturing the DVB stream and displaying it on the TV. The board is running on Linux OS. Problem Description: I am trying to read data from a large file(approximately 2 GB) on USB using O_DIRECT flag. Here is the relevant o_direct alignment code snippet: char subblk[BLKSIZE]; open (filename2,O_CREAT|O_WRONLY|O_DIRECT,S_IRWXU|S_IRWXG|S_IRWXO); read (fp,subblk,BLKSIZE); It says read failed with error number 22 - "EINVAL 22 /* Invalid argument" To clarify whether this a programming issue or some architecture dependent problem, I ran the same code on my Desktop system, it worked perfectly fine and I was able to print the characters what I just read. What is the reason it is failing on my ST40 board? c linux io share|improve this question asked May 9 '12 at 9:07 mk.. 4,11863453 Was the test on the desktop also reading from (the very same) external USB storage device? –unwind May 9 '12 at 9:15 My official system is Windows. There is a remote Linux server on which we are given logins. So i cannot connect a USB device to that system. Hence i copied the same file into my local working directory and tested the code. It was working fine.. –mk.. May 9 '12 at 9:34 add a comment| 3 Answers 3 active oldest votes up vote 9 down vote You should align buffer by filesystem block boundary. To achieve this you should not use bu
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Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each o_direct ext4 other. Join them; it only takes a minute: Sign up direct io - O_DIRECT seems not working when write to file up vote 1 down vote favorite 1 On linux (Linux 3.16.0-38-generic #52~14.04.1-Ubuntu x86_64 GNU/Linux), When try to http://stackoverflow.com/questions/10512987/o-direct-flag-not-working write to a file via direct io with O_DIRECT flag enabled, it seems after write, the file is still empty, please help. By the way, I am aware of direct io should normally be used with program level cache, following program just want to have a test on direct io. direct_io_test.c: // direct io test #define _GNU_SOURCE #include
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of http://unix.stackexchange.com/questions/6467/use-of-o-direct-on-linux this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Unix & Linux Questions Tags Users Badges Unanswered Ask Question _ https://lwn.net/Articles/457667/ Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. Join them; it only takes a minute: Sign up Here's how how to it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top Use of O_DIRECT on Linux up vote 16 down vote favorite 8 If this question is too programmer oriented, let me know. I wonder if there are people familiar with the O_DIRECT flag for the open() system call on Linux 2.6? Linus disparages its o_direct write error use, however high performance file writing seems to indicate its use. I would like to know of any real world experience and recommendations. More info: The application that I am using does maintain its own cache, and in doing so attains an average of 5x or more speed up. When writing to file, the contents of the cache must be written out to the filesystem cache, which seems redundant and a performance concern. linux kernel files performance programming share|improve this question edited Oct 26 '15 at 21:28 ArekBulski 29812 asked Jan 26 '11 at 2:50 casualunixer 3601615 add a comment| 5 Answers 5 active oldest votes up vote 13 down vote Ok, you ask for experiences, this makes the question a little subjective and argumentative, but passable. Linus said that referring to the uses that people usually attribute to O_DIRECT, and for those uses, IMO Linus is mostly correct. Even if you do direct I/O, you cannot transfer data to/from devices directly to your program statements, you need a buffer that is filled (by the program or the device) and transferred through a system call to the other end. Also, to make it effici
reaches disk This article brought to you by LWN subscribersSubscribers to LWN.net made this article — and everything that surrounds it — possible. If you appreciate our content, please buy a subscription and make the next set of articles possible. September 7, 2011 This article was contributed by Jeff Moyer In a perfect world, there would be no operating system crashes, power outages or disk failures, and programmers wouldn't have to worry about coding for these corner cases. Unfortunately, these failures are more common than one would expect. The purpose of this document is to describe the path data takes from the application down to the storage, concentrating on places where data is buffered, and to then provide best practices for ensuring data is committed to stable storage so it is not lost along the way in the case of an adverse event. The main focus is on the C programming language, though the system calls mentioned should translate fairly easily to most other languages. I/O buffering In order to program for data integrity, it is crucial to have an understanding of the overall system architecture. Data can travel through several layers before it finally reaches stable storage, as seen below: At the top is the running application which has data that it needs to save to stable storage. That data starts out as one or more blocks of memory, or buffers, in the application itself. Those buffers can also be handed to a library, which may perform its own buffering. Regardless of whether data is buffered in application buffers or by a library, the data lives in the application's address space. The next layer that the data goes through is the kernel, which keeps its own version of a write-back cache called the page cache. Dirty pages can live in the page cache for an indeterminate amount of time, depending on overall system load