On Wed, 9 Jul 2014, loody wrote:
> hi all:
> I try 2 methods today but there is no read command firing from usb
> host to device
> (I double check the existence of command by CATC protocol analyzer)
> appreciate all your kind suggestion.
>
> 1. use busybox like below command
> dd if=/dev/sda1 of=/dev/null bs=512 count=1 conv=sync
> my dd in busybox doesn't have iflags option
> # ./busybox.new dd help
>
> BusyBox v1.19.2 (2014-07-09 13:43:36 CST) multi-call binary.
> Usage: dd [if=FILE] [of=FILE] [ibs=N] [obs=N] [bs=N] [count=N] [skip=N]
> [seek=N] [conv=notrunc|noerror|sync|fsync]
> Copy a file with converting and formatting
> if=FILE Read from FILE instead of stdin
> of=FILE Write to FILE instead of stdout
> bs=N Read and write N bytes at a time
> ibs=N Read N bytes at a time
> obs=N Write N bytes at a time
> count=N Copy only N input blocks
> skip=N Skip N input blocks
> seek=N Skip N output blocks
> conv=notrunc Don't truncate output file
> conv=noerror Continue after read errors
> conv=sync Pad blocks with zeros
> conv=fsync Physically write data out before finishing
>
> 2. write c source file and open with O_DIRECT flag.
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
>
> char message[] = "/mnt/usb/4854344154343452/test.txt";
> int main()
> {
> int fd;
> char buffer[5];
> int count = 0;
> char *buf="1234567890";
> if((fd=open(message,O_CREAT|O_TRUNC|O_RDWR|O_DIRECT, 0777))<0)
> {
> perror("open");
> return -1;
> }
> printf("fd=%d\n", fd);
> write(fd, buf, strlen(buf));
> while(1){
> lseek(fd,0,SEEK_SET);
> sleep(3);
> count = read(fd, buffer, 3);
> printf("count=%d,%x,%x,%x\n", count,buffer[0],buffer[1],buffer[2]);
> }
>
> }
You can do what you want by using the SCSI Generic API. See the Linux
SCSI Generic (sg) HOWTO:
http://tldp.org/HOWTO/SCSI-Generic-HOWTO/
With the proper ioctl call, you can send a READ(10) command telling the
drive to read one block starting from block 0.
Alan Stern
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