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Step.30 direct_IO method of address_space
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‎030_direct_io/Makefile

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ME2FS_SOURCE = me2fs_main.c me2fs_super.c me2fs_block.c me2fs_inode.c \
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me2fs_dir.c me2fs_namei.c me2fs_file.c me2fs_ialloc.c \
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me2fs_symlink.c me2fs_sysfs.c me2fs_ioctl.c
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obj-m += me2fs.o
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me2fs-objs := $(ME2FS_SOURCE:.c=.o)
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all:
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make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
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insmod:
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sudo insmod me2fs.ko
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rmmod:
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sudo rmmod me2fs.ko
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mount:
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sudo mount -t me2fs -o loop ../ext2.img ../mnt
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mount2:
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sudo insmod me2fs.ko
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sudo mount -t me2fs -o loop ../ext2.img ../mnt
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remount:
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sudo mount -o remount$(OPT) ../mnt
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umount:
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sudo umount ../mnt
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umount2:
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sudo umount ../mnt
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sudo rmmod me2fs.ko
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clean:
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make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

‎030_direct_io/direct_io.c

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/********************************************************************************
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File : direct_io.c
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Description : example of direct io
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*********************************************************************************/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <errno.h>
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#include <string.h>
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#include <stdlib.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include <fcntl.h>
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/*
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==================================================================================
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Prototype Statement
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==================================================================================
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*/
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/*
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==================================================================================
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DEFINES
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==================================================================================
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*/
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/*
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==================================================================================
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Management
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==================================================================================
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*/
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static char write_strings[ ] = "direct io example";
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/*
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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< Open Functions >
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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*/
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/*
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_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
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Function :main
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Input :int argc
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< number of arguments >
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char *argv[ ]
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< arguments >
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Output :void
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Return :int
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< result >
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Description :direct io
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_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
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*/
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int main( int argc, char *argv[ ] )
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{
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int err;
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char *pathname;
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int fd;
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long align;
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char *buf = NULL;
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struct stat stat_buf;
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size_t block_size;
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if( argc < 2 )
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{
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fprintf( stderr, "./%s pathname\n", argv[ 0 ] );
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return( -1 );
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}
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/* ------------------------------------------------------------------------ */
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/* open a file with O_DIRECT flag */
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/* ------------------------------------------------------------------------ */
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pathname = argv[ 1 ];
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fd = open( pathname, O_CREAT | O_RDWR | O_DIRECT, 0664 );
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if( fd < 0 )
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{
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perror( "open : " );
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return( fd );
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}
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/* ------------------------------------------------------------------------ */
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/* get block size of the filesystem */
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/* ------------------------------------------------------------------------ */
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err = fstat( fd, &stat_buf );
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if( err < 0 )
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{
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perror( "fstat : " );
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goto err_close;
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}
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block_size = ( size_t )stat_buf.st_blksize;
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/* ------------------------------------------------------------------------ */
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/* get alignment restriction */
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/* ------------------------------------------------------------------------ */
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align = fpathconf( fd, _PC_REC_XFER_ALIGN );
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if( align < 0 )
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{
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fprintf( stderr, "error : fpathconf : %ld\n", align );
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goto err_close;
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}
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/* ------------------------------------------------------------------------ */
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/* allocate aligned memory */
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/* ------------------------------------------------------------------------ */
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err = posix_memalign( ( void** )&buf, ( size_t )align, block_size );
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if( err < 0 )
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{
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perror( "posix_memalign : " );
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goto err_close;
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}
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/* ------------------------------------------------------------------------ */
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/* write via direct io */
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/* ------------------------------------------------------------------------ */
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memset( buf, '\0', block_size );
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memcpy( buf, write_strings, sizeof( write_strings ) );
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err = write( fd, buf, block_size );
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if( err < 0 )
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{
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perror( "write : " );
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}
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/* ------------------------------------------------------------------------ */
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/* free memory */
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/* ------------------------------------------------------------------------ */
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err_write:
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free( buf );
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/* ------------------------------------------------------------------------ */
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/* close a file */
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/* ------------------------------------------------------------------------ */
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err_close:
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if( ( err = close( fd ) ) < 0 )
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{
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perror( "close : " );
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}
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return( err );
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}
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/*
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_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
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Function :void
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Input :void
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Output :void
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Return :void
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Description :void
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_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
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*/
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/*
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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< Local Functions >
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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*/
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/*
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==================================================================================
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Function :void
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Input :void
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Output :void
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Return :void
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Description :void
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==================================================================================
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*/

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