hi NeilBrown:
we use below c source but there is no read command firing from usb
host to device.
except O_DIRECT, is there any flag we need to use?
appreciate all your kind help,
#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]);
}
}
2014-07-08 11:01 GMT+08:00 NeilBrown <neilb@xxxxxxx>:
> On Mon, 7 Jul 2014 22:42:29 +0800 loody <miloody@xxxxxxxxx> wrote:
>
>> hi all:
>> we met a USB Hard Disk that will go to suspend if host stop
>> sending scsi read command over 5mins.
>> To save the IO, kernel will keep the file in page cache as much as
>> he can and under this circumstances, the read command may disappear
>> for a while longer enough to cause the device suspend.
>>
>> is there any kernel config or module parameter can do the dummy
>> read periodically, even the sector 0 (MBR) is fine.
>> or is there any kernel api I can use to read sector 0(MBR) maybe
>> every 4mins?
>>
>> appreciate your help in advance,
>> --
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>
> Open the device with O_DIRECT and read a block every 4 minutes.
> That should keep it awake.
>
> NeilBrown
--
Regards,
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